Merge pull request #2 from eugenp/master

Syncing

.gitignore

@@ -85,5 +85,6 @@ transaction.log
 *-shell.log
 
 apache-cxf/cxf-aegis/baeldung.xml
+testing-modules/report-*.json
 
 libraries-2/*.db

algorithms-miscellaneous-6/README.md

@@ -7,4 +7,6 @@
 - [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
 - [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
 - [The Caesar Cipher in Java](https://www.baeldung.com/java-caesar-cipher)
+- [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
+- [Finding Top K Elements in an Array](https://www.baeldung.com/java-array-top-elements)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-5)

algorithms-searching/README.md

@@ -3,6 +3,7 @@
 This module contains articles about searching algorithms.
 
 ### Relevant articles:
+
 - [Binary Search Algorithm in Java](https://www.baeldung.com/java-binary-search)
 - [Depth First Search in Java](https://www.baeldung.com/java-depth-first-search)
 - [Interpolation Search in Java](https://www.baeldung.com/java-interpolation-search)
@@ -11,3 +12,4 @@ This module contains articles about searching algorithms.
 - [Monte Carlo Tree Search for Tic-Tac-Toe Game](https://www.baeldung.com/java-monte-carlo-tree-search)
 - [Range Search Algorithm in Java](https://www.baeldung.com/java-range-search)
 - [Fast Pattern Matching of Strings Using Suffix Tree](https://www.baeldung.com/java-pattern-matching-suffix-tree)
+- [Find the Kth Smallest Element in Two Sorted Arrays](https://www.baeldung.com/java-kth-smallest-element-in-sorted-arrays)

algorithms-searching/src/main/java/com/baeldung/algorithms/kthsmallest/KthSmallest.java

@@ -0,0 +1,126 @@
+package com.baeldung.algorithms.kthsmallest;
+
+import java.util.Arrays;
+import java.util.NoSuchElementException;
+
+import static java.lang.Math.max;
+import static java.lang.Math.min;
+
+public class KthSmallest {
+
+    public static int findKthSmallestElement(int k, int[] list1, int[] list2)  throws NoSuchElementException, IllegalArgumentException {
+
+        checkInput(k, list1, list2);
+
+        // we are looking for the minimum value
+        if(k == 1) {
+            return min(list1[0], list2[0]);
+        }
+
+        // we are looking for the maximum value
+        if(list1.length + list2.length == k) {
+            return max(list1[list1.length-1], list2[list2.length-1]);
+        }
+
+        // swap lists if needed to make sure we take at least one element from list1
+        if(k <= list2.length && list2[k-1] < list1[0]) {
+            int[] list1_ = list1;
+            list1 = list2;
+            list2 = list1_;
+        }
+
+        // correct left boundary if k is bigger than the size of list2
+        int left = k < list2.length ? 0 : k - list2.length - 1;
+
+        // the inital right boundary cannot exceed the list1
+        int right = min(k-1, list1.length - 1);
+
+        int nElementsList1, nElementsList2;
+
+        // binary search
+        do {
+            nElementsList1 = ((left + right) / 2) + 1;
+            nElementsList2 = k - nElementsList1;
+
+            if(nElementsList2 > 0) {
+                if (list1[nElementsList1 - 1] > list2[nElementsList2 - 1]) {
+                    right = nElementsList1 - 2;
+                } else {
+                    left = nElementsList1;
+                }
+            }
+        } while(!kthSmallesElementFound(list1, list2, nElementsList1, nElementsList2));
+
+        return nElementsList2 == 0 ? list1[nElementsList1-1] : max(list1[nElementsList1-1], list2[nElementsList2-1]);
+    }
+
+    private static boolean kthSmallesElementFound(int[] list1, int[] list2, int nElementsList1, int nElementsList2) {
+
+        // we do not take any element from the second list
+        if(nElementsList2 < 1) {
+            return true;
+        }
+
+        if(list1[nElementsList1-1] == list2[nElementsList2-1]) {
+            return true;
+        }
+
+        if(nElementsList1 == list1.length) {
+            return list1[nElementsList1-1] <= list2[nElementsList2];
+        }
+
+        if(nElementsList2 == list2.length) {
+            return list2[nElementsList2-1] <= list1[nElementsList1];
+        }
+
+        return list1[nElementsList1-1] <= list2[nElementsList2] && list2[nElementsList2-1] <= list1[nElementsList1];
+    }
+
+
+    private static void checkInput(int k, int[] list1, int[] list2) throws NoSuchElementException, IllegalArgumentException {
+
+        if(list1 == null || list2 == null || k < 1) {
+            throw new IllegalArgumentException();
+        }
+
+        if(list1.length == 0 || list2.length == 0) {
+            throw new IllegalArgumentException();
+        }
+
+        if(k > list1.length + list2.length) {
+            throw new NoSuchElementException();
+        }
+    }
+
+    public static int getKthElementSorted(int[] list1, int[] list2, int k) {
+
+        int length1 = list1.length, length2 = list2.length;
+        int[] combinedArray = new int[length1 + length2];
+        System.arraycopy(list1, 0, combinedArray, 0, list1.length);
+        System.arraycopy(list2, 0, combinedArray, list1.length, list2.length);
+        Arrays.sort(combinedArray);
+
+        return combinedArray[k-1];
+    }
+
+    public static int getKthElementMerge(int[] list1, int[] list2, int k) {
+
+        int i1 = 0, i2 = 0;
+
+        while(i1 < list1.length && i2 < list2.length && (i1 + i2) < k) {
+            if(list1[i1] < list2[i2]) {
+                i1++;
+            } else {
+                i2++;
+            }
+        }
+
+        if((i1 + i2) < k) {
+            return i1 < list1.length ? list1[k - i2 - 1] : list2[k - i1 - 1];
+        } else if(i1 > 0 && i2 > 0) {
+            return Math.max(list1[i1-1], list2[i2-1]);
+        } else {
+            return i1 == 0 ? list2[i2-1] : list1[i1-1];
+        }
+    }
+}

algorithms-searching/src/test/java/com/baeldung/algorithms/kthsmallest/KthSmallestUnitTest.java

@@ -0,0 +1,288 @@
+package com.baeldung.algorithms.kthsmallest;
+
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
+
+import java.util.*;
+
+import static com.baeldung.algorithms.kthsmallest.KthSmallest.*;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class KthSmallestUnitTest {
+
+    @Nested
+    class Exceptions {
+
+        @Test
+        public void when_at_least_one_list_is_null_then_an_exception_is_thrown() {
+
+            Executable executable1 = () -> findKthSmallestElement(1, null, null);
+            Executable executable2 = () -> findKthSmallestElement(1, new int[]{2}, null);
+            Executable executable3 = () -> findKthSmallestElement(1, null, new int[]{2});
+
+            assertThrows(IllegalArgumentException.class, executable1);
+            assertThrows(IllegalArgumentException.class, executable2);
+            assertThrows(IllegalArgumentException.class, executable3);
+        }
+
+        @Test
+        public void when_at_least_one_list_is_empty_then_an_exception_is_thrown() {
+
+            Executable executable1 = () -> findKthSmallestElement(1, new int[]{}, new int[]{2});
+            Executable executable2 = () -> findKthSmallestElement(1, new int[]{2}, new int[]{});
+            Executable executable3 = () -> findKthSmallestElement(1, new int[]{}, new int[]{});
+
+            assertThrows(IllegalArgumentException.class, executable1);
+            assertThrows(IllegalArgumentException.class, executable2);
+            assertThrows(IllegalArgumentException.class, executable3);
+        }
+
+        @Test
+        public void when_k_is_smaller_than_0_then_an_exception_is_thrown() {
+            Executable executable1 = () -> findKthSmallestElement(-1, new int[]{2}, new int[]{2});
+            assertThrows(IllegalArgumentException.class, executable1);
+        }
+
+        @Test
+        public void when_k_is_smaller_than_1_then_an_exception_is_thrown() {
+            Executable executable1 = () -> findKthSmallestElement(0, new int[]{2}, new int[]{2});
+            assertThrows(IllegalArgumentException.class, executable1);
+        }
+
+        @Test
+        public void when_k_bigger_then_the_two_lists_then_an_exception_is_thrown() {
+            Executable executable1 = () -> findKthSmallestElement(6, new int[]{1, 5, 6}, new int[]{2, 5});
+            assertThrows(NoSuchElementException.class, executable1);
+        }
+
+    }
+
+    @Nested
+    class K_is_smaller_than_the_size_of_list1_and_the_size_of_list2 {
+
+        @Test
+        public void when_k_is_1_then_the_smallest_element_is_returned_from_list1() {
+            int result = findKthSmallestElement(1, new int[]{2, 7}, new int[]{3, 5});
+            assertEquals(2, result);
+        }
+
+        @Test
+        public void when_k_is_1_then_the_smallest_element_is_returned_list2() {
+            int result = findKthSmallestElement(1, new int[]{3, 5}, new int[]{2, 7});
+            assertEquals(2, result);
+        }
+
+        @Test
+        public void when_kth_element_is_smallest_element_and_occurs_in_both_lists() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(1, list1, list2);
+            assertEquals(1, result);
+        }
+
+        @Test
+        public void when_kth_element_is_smallest_element_and_occurs_in_both_lists2() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(2, list1, list2);
+            assertEquals(1, result);
+        }
+
+        @Test
+        public void when_kth_element_is_largest_element_and_occurs_in_both_lists_1() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(5, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void when_kth_element_is_largest_element_and_occurs_in_both_lists_2() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(6, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void when_kth_element_and_occurs_in_both_lists() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{0, 2, 3};
+            int result = findKthSmallestElement(3, list1, list2);
+            assertEquals(2, result);
+        }
+
+        @Test
+        public void and_kth_element_is_in_first_list() {
+            int[] list1 = new int[]{1,2,3,4};
+            int[] list2 = new int[]{1,3,4,5};
+            int result = findKthSmallestElement(3,  list1, list2);
+            assertEquals(2, result);
+        }
+
+        @Test
+        public void and_kth_is_in_second_list() {
+            int[] list1 = new int[]{1,3,4,4};
+            int[] list2 = new int[]{1,2,4,5};
+            int result = findKthSmallestElement(3,  list1, list2);
+            assertEquals(2, result);
+        }
+
+        @Test
+        public void and_elements_in_first_list_are_all_smaller_than_second_list() {
+            int[] list1 = new int[]{1,3,7,9};
+            int[] list2 = new int[]{11,12,14,15};
+            int result = findKthSmallestElement(3,  list1, list2);
+            assertEquals(7, result);
+        }
+
+        @Test
+        public void and_elements_in_first_list_are_all_smaller_than_second_list2() {
+            int[] list1 = new int[]{1,3,7,9};
+            int[] list2 = new int[]{11,12,14,15};
+            int result = findKthSmallestElement(4,  list1, list2);
+            assertEquals(9, result);
+        }
+
+        @Test
+        public void and_only_elements_from_second_list_are_part_of_result() {
+            int[] list1 = new int[]{11,12,14,15};
+            int[] list2 = new int[]{1,3,7,9};
+            int result = findKthSmallestElement(3,  list1, list2);
+            assertEquals(7, result);
+        }
+
+        @Test
+        public void and_only_elements_from_second_list_are_part_of_result2() {
+            int[] list1 = new int[]{11,12,14,15};
+            int[] list2 = new int[]{1,3,7,9};
+            int result = findKthSmallestElement(4,  list1, list2);
+            assertEquals(9, result);
+        }
+    }
+
+    @Nested
+    class K_is_bigger_than_the_size_of_at_least_one_of_the_lists {
+
+        @Test
+        public void k_is_smaller_than_list1_and_bigger_than_list2() {
+            int[] list1 = new int[]{1, 2, 3, 4, 7, 9};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(5, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void k_is_bigger_than_list1_and_smaller_than_list2() {
+            int[] list1 = new int[]{1, 2, 3};
+            int[] list2 = new int[]{1, 2, 3, 4, 7, 9};
+            int result = findKthSmallestElement(5, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void when_k_is_bigger_than_the_size_of_both_lists_and_elements_in_second_list_are_all_smaller_than_first_list() {
+            int[] list1 = new int[]{9, 11, 13, 55};
+            int[] list2 = new int[]{1, 2, 3, 7};
+            int result = findKthSmallestElement(6, list1, list2);
+            assertEquals(11, result);
+        }
+
+        @Test
+        public void when_k_is_bigger_than_the_size_of_both_lists_and_elements_in_second_list_are_all_bigger_than_first_list() {
+            int[] list1 = new int[]{1, 2, 3, 7};
+            int[] list2 = new int[]{9, 11, 13, 55};
+            int result = findKthSmallestElement(6, list1, list2);
+            assertEquals(11, result);
+        }
+
+        @Test
+        public void when_k_is_bigger_than_the_size_of_both_lists() {
+            int[] list1 = new int[]{3, 7, 9, 11, 55};
+            int[] list2 = new int[]{1, 2, 3, 7, 13};
+            int result = findKthSmallestElement(7, list1, list2);
+            assertEquals(9, result);
+        }
+
+        @Test
+        public void when_k_is_bigger_than_the_size_of_both_lists_and_list1_has_more_elements_than_list2() {
+            int[] list1 = new int[]{3, 7, 9, 11, 55, 77, 100, 200};
+            int[] list2 = new int[]{1, 2, 3, 7, 13};
+            int result = findKthSmallestElement(11, list1, list2);
+            assertEquals(77, result);
+        }
+
+        @Test
+        public void max_test() {
+            int[] list1 = new int[]{100, 200};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(4, list1, list2);
+            assertEquals(100, result);
+        }
+
+        @Test
+        public void max_test2() {
+            int[] list1 = new int[]{100, 200};
+            int[] list2 = new int[]{1, 2, 3};
+            int result = findKthSmallestElement(5, list1, list2);
+            assertEquals(200, result);
+        }
+
+        @Test
+        public void when_k_is_smaller_than_the_size_of_both_lists_and_kth_element_in_list2() {
+            int[] list1 = new int[]{1, 2, 5};
+            int[] list2 = new int[]{1, 3, 4, 7};
+            int result = findKthSmallestElement(4, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void when_k_is_smaller_than_the_size_of_both_lists_and_kth_element_is_smallest_in_list2() {
+            int[] list1 = new int[]{1, 2, 5};
+            int[] list2 = new int[]{3, 4, 7};
+            int result = findKthSmallestElement(3, list1, list2);
+            assertEquals(3, result);
+        }
+
+        @Test
+        public void when_k_is_smaller_than_the_size_of_both_lists_and_kth_element_is_smallest_in_list23() {
+            int[] list1 = new int[]{3, 11, 27, 53, 90};
+            int[] list2 = new int[]{4, 20, 21, 100};
+            int result = findKthSmallestElement(5, list1, list2);
+            assertEquals(21, result);
+        }
+    }
+
+//    @Test
+//    public void randomTests() {
+//        IntStream.range(1, 100000).forEach(i -> random());
+//    }
+
+    private void random() {
+
+        Random random = new Random();
+        int length1 = (Math.abs(random.nextInt())) % 1000 + 1;
+        int length2 = (Math.abs(random.nextInt())) % 1000 + 1;
+
+        int[] list1 = sortedRandomIntArrayOfLength(length1);
+        int[] list2 = sortedRandomIntArrayOfLength(length2);
+
+        int k = (Math.abs(random.nextInt()) % (length1 + length2)) + 1 ;
+
+        int result = findKthSmallestElement(k,  list1, list2);
+
+        int result2 = getKthElementSorted(list1, list2, k);
+
+        int result3 = getKthElementMerge(list1, list2, k);
+
+        assertEquals(result2, result);
+        assertEquals(result2, result3);
+    }
+
+    private int[] sortedRandomIntArrayOfLength(int length) {
+        int[] intArray = new Random().ints(length).toArray();
+        Arrays.sort(intArray);
+        return intArray;
+    }
+}

apache-cxf/README.md

@@ -7,4 +7,3 @@ This module contains articles about Apache CXF
 - [Apache CXF Support for RESTful Web Services](https://www.baeldung.com/apache-cxf-rest-api)
 - [A Guide to Apache CXF with Spring](https://www.baeldung.com/apache-cxf-with-spring)
 - [Introduction to Apache CXF](https://www.baeldung.com/introduction-to-apache-cxf)
-- [Server-Sent Events (SSE) In JAX-RS](https://www.baeldung.com/java-ee-jax-rs-sse)

apache-cxf/sse-jaxrs/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Server-Sent Events (SSE) In JAX-RS](https://www.baeldung.com/java-ee-jax-rs-sse)

apache-poi/README.md

@@ -3,9 +3,11 @@
 This module contains articles about Apache POI
 
 ### Relevant Articles:
+
 - [Microsoft Word Processing in Java with Apache POI](https://www.baeldung.com/java-microsoft-word-with-apache-poi)
 - [Working with Microsoft Excel in Java](https://www.baeldung.com/java-microsoft-excel)
 - [Creating a MS PowerPoint Presentation in Java](https://www.baeldung.com/apache-poi-slideshow)
 - [Merge Cells in Excel Using Apache POI](https://www.baeldung.com/java-apache-poi-merge-cells)
 - [Get String Value of Excel Cell with Apache POI](https://www.baeldung.com/java-apache-poi-cell-string-value)
 - [Read Excel Cell Value Rather Than Formula With Apache POI](https://www.baeldung.com/apache-poi-read-cell-value-formula)
+- [Setting Formulas in Excel with Apache POI](https://www.baeldung.com/java-apache-poi-set-formulas)

apache-poi/src/main/java/com/baeldung/poi/excel/setformula/ExcelFormula.java

@@ -0,0 +1,26 @@
+package com.baeldung.poi.excel.setformula;
+
+import org.apache.poi.xssf.usermodel.XSSFCell;
+import org.apache.poi.xssf.usermodel.XSSFFormulaEvaluator;
+import org.apache.poi.xssf.usermodel.XSSFSheet;
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+public class ExcelFormula {
+    public double setFormula(String fileLocation, XSSFWorkbook wb, String formula) throws IOException {
+        XSSFSheet sheet = wb.getSheetAt(0);
+        int lastCellNum = sheet.getRow(0).getLastCellNum();
+        XSSFCell formulaCell = sheet.getRow(0).createCell(lastCellNum);
+        formulaCell.setCellFormula(formula);
+        XSSFFormulaEvaluator formulaEvaluator = wb.getCreationHelper().createFormulaEvaluator();
+        formulaEvaluator.evaluateFormulaCell(formulaCell);
+        FileOutputStream fileOut = new FileOutputStream(new File(fileLocation));
+        wb.write(fileOut);
+        wb.close();
+        fileOut.close();
+        return formulaCell.getNumericCellValue();
+    }
+}

apache-poi/src/test/java/com/baeldung/poi/excel/setformula/ExcelFormulaUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.poi.excel.setformula;
+
+import org.apache.poi.ss.util.CellReference;
+import org.apache.poi.xssf.usermodel.XSSFSheet;
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+import org.junit.Assert;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.nio.file.Paths;
+
+class ExcelFormulaUnitTest {
+    private static String FILE_NAME = "com/baeldung/poi/excel/setformula/SetFormulaTest.xlsx";
+    private String fileLocation;
+    private ExcelFormula excelFormula;
+
+    @BeforeEach
+    public void setup() throws URISyntaxException {
+        fileLocation = Paths.get(ClassLoader.getSystemResource(FILE_NAME).toURI()).toString();
+        excelFormula = new ExcelFormula();
+    }
+
+    @Test
+    void givenExcelData_whenSetFormula_thenSuccess() throws IOException {
+        FileInputStream inputStream = new FileInputStream(new File(fileLocation));
+        XSSFWorkbook wb = new XSSFWorkbook(inputStream);
+        XSSFSheet sheet = wb.getSheetAt(0);
+        double resultColumnA = 0;
+        double resultColumnB = 0;
+        for (int row = 0; row <= sheet.getLastRowNum(); row++) {
+            resultColumnA += sheet.getRow(row).getCell(0).getNumericCellValue();
+            resultColumnB += sheet.getRow(row).getCell(1).getNumericCellValue();
+        }
+        String colNameA = CellReference.convertNumToColString(0);
+        String colNameB = CellReference.convertNumToColString(1);
+        String startCellA = colNameA + 1;
+        String stopCellA = colNameA + (sheet.getLastRowNum() + 1);
+        String sumFormulaForColumnA = String.format("SUM(%s:%s)", startCellA, stopCellA);
+        String startCellB = colNameB + 1;
+        String stopCellB = colNameB + (sheet.getLastRowNum() + 1);
+        String sumFormulaForColumnB = String.format("SUM(%s:%s)", startCellB, stopCellB);
+
+        double resultValue = excelFormula.setFormula(fileLocation, wb, sumFormulaForColumnA + "-" + sumFormulaForColumnB);
+
+        Assert.assertEquals(resultColumnA - resultColumnB, resultValue, 0d);
+    }
+}

apache-shiro/README.md

@@ -6,4 +6,4 @@ This module contains articles about Apache Shiro
 
 - [Introduction to Apache Shiro](https://www.baeldung.com/apache-shiro)
 - [Permissions-Based Access Control with Apache Shiro](https://www.baeldung.com/apache-shiro-access-control)
-
+- [Spring Security vs Apache Shiro](https://www.baeldung.com/spring-security-vs-apache-shiro)

core-groovy/README.md

@@ -13,4 +13,5 @@ This module contains articles about core Groovy concepts
 - [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
 - [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)
 - [Convert String to Integer in Groovy](https://www.baeldung.com/groovy-convert-string-to-integer)
+- [Groovy Variable Scope](https://www.baeldung.com/groovy/variable-scope)
 - [[More -->]](/core-groovy-2)

core-java-modules/core-java-10/README.md

@@ -9,3 +9,4 @@ This module contains articles about Java 10 core features
 - [Copy a List to Another List in Java](http://www.baeldung.com/java-copy-list-to-another)
 - [Deep Dive Into the New Java JIT Compiler – Graal](https://www.baeldung.com/graal-java-jit-compiler)
 - [Copying Sets in Java](https://www.baeldung.com/java-copy-sets)
+- [Converting between a List and a Set in Java](https://www.baeldung.com/convert-list-to-set-and-set-to-list)

core-java-modules/core-java-10/pom.xml

@@ -1,22 +1,29 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project
-    xmlns="http://maven.apache.org/POM/4.0.0"
+        xmlns="http://maven.apache.org/POM/4.0.0"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <artifactId>core-java-10</artifactId>
     <version>0.1.0-SNAPSHOT</version>
     <name>core-java-10</name>
     <packaging>jar</packaging>
-    <url>http://maven.apache.org</url>
 
     <parent>
-        <groupId>com.baeldung</groupId>
+        <groupId>com.baeldung.core-java-modules</groupId>
-        <artifactId>parent-modules</artifactId>
+        <artifactId>core-java-modules</artifactId>
-        <version>1.0.0-SNAPSHOT</version>
+        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../../</relativePath>
+        <relativePath>../</relativePath>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -34,6 +41,7 @@
     <properties>
         <maven.compiler.source.version>10</maven.compiler.source.version>
         <maven.compiler.target.version>10</maven.compiler.target.version>
+        <commons-collections4.version>4.1</commons-collections4.version>
     </properties>
 
 </project>

core-java-modules/core-java-10/src/test/java/com/baeldung/java10/collections/conversion/ListSetConversionUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.java10.collections.conversion;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
+import org.apache.commons.collections4.CollectionUtils;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class ListSetConversionUnitTest {
+
+    // Set -> List; List -> Set
+
+    @Test
+    public final void givenUsingCoreJava_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = new ArrayList<>(sourceSet);
+    }
+
+    @Test
+    public final void givenUsingCoreJava_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = new HashSet<>(sourceList);
+    }
+
+    @Test
+    public void givenUsingJava10_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = List.copyOf(sourceSet);
+    }
+
+    @Test
+    public void givenUsingJava10_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = Set.copyOf(sourceList);
+    }
+
+    @Test
+    public final void givenUsingGuava_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = Lists.newArrayList(sourceSet);
+    }
+
+    @Test
+    public final void givenUsingGuava_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = Sets.newHashSet(sourceList);
+    }
+
+    @Test
+    public final void givenUsingCommonsCollections_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+
+        final Set<Integer> targetSet = new HashSet<>(6);
+        CollectionUtils.addAll(targetSet, sourceList);
+    }
+
+    @Test
+    public final void givenUsingCommonsCollections_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+
+        final List<Integer> targetList = new ArrayList<>(6);
+        CollectionUtils.addAll(targetList, sourceSet);
+    }
+}

core-java-modules/core-java-11/README.md

@@ -8,7 +8,7 @@ This module contains articles about Java 11 core features
 - [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
 - [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)
 - [Java 11 Nest Based Access Control](https://www.baeldung.com/java-nest-based-access-control)
-- [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
+- [Exploring the New HTTP Client in Java](https://www.baeldung.com/java-9-http-client)
 - [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
 - [Guide to jlink](https://www.baeldung.com/jlink)
 - [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseDateTimeFormatterUnitTest.java

@@ -31,6 +31,6 @@ public class UseDateTimeFormatterUnitTest {
     public void givenALocalDate_whenFormattingWithStyleAndLocale_thenPass() {
         String result = subject.formatWithStyleAndLocale(localDateTime, FormatStyle.MEDIUM, Locale.UK);
 
-        assertThat(result).isEqualTo("25 Jan 2015, 06:30:00");
+        assertThat(result).isEqualTo("25-Jan-2015 06:30:00");
     }
 }

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseToInstantUnitTest.java

@@ -3,6 +3,7 @@ package com.baeldung.datetime;
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.time.LocalDateTime;
+import java.time.ZoneId;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.GregorianCalendar;
@@ -24,10 +25,11 @@ public class UseToInstantUnitTest {
 
     @Test
     public void givenADate_whenConvertingToLocalDate_thenAsExpected() {
-        Date givenDate = new Date(1465817690000L);
+        LocalDateTime currentDateTime = LocalDateTime.now();
+        Date givenDate = Date.from(currentDateTime.atZone(ZoneId.systemDefault()).toInstant());
 
         LocalDateTime localDateTime = subject.convertDateToLocalDate(givenDate);
 
-        assertThat(localDateTime).isEqualTo("2016-06-13T13:34:50");
+        assertThat(localDateTime).isEqualTo(currentDateTime);
     }
 }

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseZonedDateTimeUnitTest.java

@@ -54,7 +54,7 @@ public class UseZonedDateTimeUnitTest {
     @Test
     public void givenAStringWithTimeZone_whenParsing_thenEqualsExpected() {
         ZonedDateTime resultFromString = zonedDateTime.getZonedDateTimeUsingParseMethod("2015-05-03T10:15:30+01:00[Europe/Paris]");
-        ZonedDateTime resultFromLocalDateTime = ZonedDateTime.of(2015, 5, 3, 11, 15, 30, 0, ZoneId.of("Europe/Paris"));
+        ZonedDateTime resultFromLocalDateTime = ZonedDateTime.of(2015, 5, 3, 10, 15, 30, 0, ZoneId.of("Europe/Paris"));
 
         assertThat(resultFromString.getZone()).isEqualTo(ZoneId.of("Europe/Paris"));
         assertThat(resultFromLocalDateTime.getZone()).isEqualTo(ZoneId.of("Europe/Paris"));

core-java-modules/core-java-9-jigsaw/src/simple-modules/main.app/com/baeldung/modules/main/MainApp.java

@@ -1,12 +1,15 @@
 package com.baeldung.modules.main;
 
+import com.baeldung.modules.hello.HelloInterface;
 import com.baeldung.modules.hello.HelloModules;
+import java.util.ServiceLoader;
 
 public class MainApp {
     public static void main(String[] args) {
         HelloModules.doSomething();
-
+        
-        HelloModules module = new HelloModules();
+        Iterable<HelloInterface> services = ServiceLoader.load(HelloInterface.class);
-        module.sayHello();
+        HelloInterface service = services.iterator().next();
+        service.sayHello();
     }
 }

core-java-modules/core-java-9-new-features/README.md

@@ -13,3 +13,5 @@ This module contains articles about core Java features that have been introduced
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
 - [Multi-Release JAR Files with Maven](https://www.baeldung.com/maven-multi-release-jars)
+- [The Difference between RxJava API and the Java 9 Flow API](https://www.baeldung.com/rxjava-vs-java-flow-api)
+- [How to Get a Name of a Method Being Executed?](https://www.baeldung.com/java-name-of-executing-method)

core-java-modules/core-java-9/README.md

@@ -9,3 +9,4 @@ This module contains articles about Java 9 core features
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)
+- [Easy Ways to Write a Java InputStream to an OutputStream](https://www.baeldung.com/java-inputstream-to-outputstream)

core-java-modules/core-java-arrays-guides/README.md

@@ -5,4 +5,4 @@ This module contains complete guides about arrays in Java
 ### Relevant Articles: 
 - [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
 - [Guide to the java.util.Arrays Class](https://www.baeldung.com/java-util-arrays)
-- [What is [Ljava.lang.Object;?]](https://www.baeldung.com/java-tostring-array)
+- [What is \[Ljava.lang.Object;?](https://www.baeldung.com/java-tostring-array)

core-java-modules/core-java-arrays-operations-advanced/README.md

@@ -3,7 +3,9 @@
 This module contains articles about advanced operations on arrays in Java. They assume some background knowledge with arrays in Java.
 
 ### Relevant Articles: 
+
 - [How to Copy an Array in Java](https://www.baeldung.com/java-array-copy)
 - [Arrays.deepEquals](https://www.baeldung.com/java-arrays-deepequals)
 - [Find Sum and Average in a Java Array](https://www.baeldung.com/java-array-sum-average)
 - [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
+- [Comparing Arrays in Java](https://www.baeldung.com/java-comparing-arrays)

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/arraycompare/Plane.java

@@ -0,0 +1,39 @@
+package com.baeldung.arraycompare;
+
+import java.util.Objects;
+
+public class Plane {
+
+    private final String name;
+
+    private final String model;
+
+    public Plane(String name, String model) {
+
+        this.name = name;
+        this.model = model;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getModel() {
+        return model;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        Plane plane = (Plane) o;
+        return Objects.equals(name, plane.name) && Objects.equals(model, plane.model);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(name, model);
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/DeepEqualsCompareUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DeepEqualsCompareUnitTest {
+
+    @Test
+    public void givenSameContents_whenDeepEquals_thenTrue() {
+        final Plane[][] planes1 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isTrue();
+    }
+
+    @Test
+    public void givenSameContentsWithDifferentOrder_whenDeepEquals_thenFalse() {
+        final Plane[][] planes1 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] { new Plane[] { new Plane("Plane 2", "B738") },
+            new Plane[] { new Plane("Plane 1", "A320") } };
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isFalse();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/EqualsCompareUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class EqualsCompareUnitTest {
+
+    @Test
+    public void givenSameContents_whenEquals_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(Arrays.equals(planes1, planes2)).isTrue();
+    }
+
+    @Test
+    public void givenSameContentsDifferentOrder_whenEquals_thenFalse() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "B738", "A320", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(Arrays.equals(planes1, planes2)).isFalse();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/LengthsCompareUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class LengthsCompareUnitTest {
+
+    @Test
+    public void givenSameContent_whenSizeCompare_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final Integer[] quantities = new Integer[] { 10, 12, 34, 45, 12, 43, 5, 2 };
+
+        assertThat(planes1).hasSize(8);
+        assertThat(quantities).hasSize(8);
+    }
+}
+

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/OrderCompareUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertTrue;
+
+public class OrderCompareUnitTest {
+    @Test
+    public void givenSameContentDifferentOrder_whenSortedAndDeepEquals_thenTrue() {
+        final Plane[][] planes1 = new Plane[][] {
+            new Plane[] { new Plane("Plane 1", "A320"), new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] {
+            new Plane[] { new Plane("Plane 2", "B738"), new Plane("Plane 1", "A320") } };
+
+        Comparator<Plane> planeComparator = (o1, o2) -> {
+            if (o1.getName()
+                .equals(o2.getName())) {
+                return o2.getModel()
+                    .compareTo(o1.getModel());
+            }
+            return o2.getName()
+                .compareTo(o1.getName());
+        };
+        Arrays.sort(planes1[0], planeComparator);
+        Arrays.sort(planes2[0], planeComparator);
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isTrue();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/ReferenceCompareUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ReferenceCompareUnitTest {
+
+    @Test
+    public void givenSameReferences_whenSame_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = planes1;
+
+        assertThat(planes1).isSameAs(planes2);
+
+        planes2[0] = "747";
+
+        assertThat(planes1).isSameAs(planes2);
+        assertThat(planes2[0]).isEqualTo("747");
+        assertThat(planes1[0]).isEqualTo("747");
+    }
+
+    @Test
+    public void givenSameContentDifferentReferences_whenSame_thenFalse() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(planes1).isNotSameAs(planes2);
+    }
+}

core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/sorting/JavaSortingUnitTest.java

@@ -5,7 +5,16 @@ import org.apache.commons.lang3.ArrayUtils;
 import org.junit.Before;
 import org.junit.Test;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
 import java.util.Map.Entry;
 
 import static org.junit.Assert.assertTrue;
@@ -138,7 +147,7 @@ public class JavaSortingUnitTest {
         HashSet<Integer> descSortedIntegersSet = new LinkedHashSet<>(Arrays.asList(255, 200, 123, 89, 88, 66, 7, 5, 1));
 
         ArrayList<Integer> list = new ArrayList<>(integersSet);
-        list.sort((i1, i2) -> i2 - i1);
+        list.sort(Comparator.reverseOrder());
         integersSet = new LinkedHashSet<>(list);
 
         assertTrue(Arrays.equals(integersSet.toArray(), descSortedIntegersSet.toArray()));

core-java-modules/core-java-collections-3/README.md

@@ -3,6 +3,7 @@
 ## Core Java Collections Cookbooks and Examples
 
 ### Relevant Articles: 
+
 - [Time Comparison of Arrays.sort(Object[]) and Arrays.sort(int[])](https://www.baeldung.com/arrays-sortobject-vs-sortint)
 - [Java ArrayList vs Vector](https://www.baeldung.com/java-arraylist-vs-vector)
 - [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)
@@ -10,3 +11,5 @@
 - [Performance of contains() in a HashSet vs ArrayList](https://www.baeldung.com/java-hashset-arraylist-contains-performance)
 - [Fail-Safe Iterator vs Fail-Fast Iterator](https://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
 - [Quick Guide to the Java Stack](https://www.baeldung.com/java-stack)
+- [Convert an Array of Primitives to a List](https://www.baeldung.com/java-primitive-array-to-list)
+- [A Guide to BitSet in Java](https://www.baeldung.com/java-bitset)

core-java-modules/core-java-collections-3/pom.xml

@@ -16,6 +16,11 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>org.openjdk.jol</groupId>
+            <artifactId>jol-core</artifactId>
+            <version>${jol-core.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
@@ -37,6 +42,7 @@
     <properties>
         <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <assertj.version>3.11.1</assertj.version>
+        <jol-core.version>0.10</jol-core.version>
     </properties>
 
 </project>

core-java-modules/core-java-collections-3/src/test/java/com/baeldung/collections/bitset/BitSetUnitTest.java

@@ -0,0 +1,178 @@
+package com.baeldung.collections.bitset;
+
+import org.junit.Test;
+import org.openjdk.jol.info.ClassLayout;
+import org.openjdk.jol.info.GraphLayout;
+
+import java.util.BitSet;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class BitSetUnitTest {
+
+    @Test
+    public void givenBoolArray_whenMemoryLayout_thenConsumeMoreThanOneBit() {
+        boolean[] bits = new boolean[1024 * 1024];
+
+        System.out.println(ClassLayout.parseInstance(bits).toPrintable());
+    }
+
+    @Test
+    public void givenBitSet_whenMemoryLayout_thenConsumeOneBitPerFlag() {
+        BitSet bitSet = new BitSet(1024 * 1024);
+
+        System.out.println(GraphLayout.parseInstance(bitSet).toPrintable());
+    }
+
+    @Test
+    public void givenBitSet_whenSetting_thenShouldBeTrue() {
+        BitSet bitSet = new BitSet();
+
+        bitSet.set(10);
+        assertThat(bitSet.get(10)).isTrue();
+
+        bitSet.set(20, 30);
+        for (int i = 20; i <= 29; i++) {
+            assertThat(bitSet.get(i)).isTrue();
+        }
+        assertThat(bitSet.get(30)).isFalse();
+
+        bitSet.set(10, false);
+        assertThat(bitSet.get(10)).isFalse();
+
+        bitSet.set(20, 30, false);
+        for (int i = 20; i <= 30; i++) {
+            assertThat(bitSet.get(i)).isFalse();
+        }
+    }
+
+    @Test
+    public void givenBitSet_whenClearing_thenShouldBeFalse() {
+        BitSet bitSet = new BitSet();
+        bitSet.set(42);
+        assertThat(bitSet.get(42)).isTrue();
+
+        bitSet.clear(42);
+        assertThat(bitSet.get(42)).isFalse();
+
+        bitSet.set(10, 20);
+        for (int i = 10; i < 20; i++) {
+            assertThat(bitSet.get(i)).isTrue();
+        }
+
+        bitSet.clear(10, 20);
+        for (int i = 10; i < 20; i++) {
+            assertThat(bitSet.get(i)).isFalse();
+        }
+
+        bitSet.set(10, 20);
+        bitSet.clear();
+        for (int i = 0; i < 100; i++) {
+            assertThat(bitSet.get(i)).isFalse();
+        }
+    }
+
+    @Test
+    public void givenBitSet_whenGettingElements_thenShouldReturnRequestedBits() {
+        BitSet bitSet = new BitSet();
+        bitSet.set(42);
+
+        assertThat(bitSet.get(42)).isTrue();
+        assertThat(bitSet.get(43)).isFalse();
+
+        bitSet.set(10, 20);
+        BitSet newBitSet = bitSet.get(10, 20);
+        for (int i = 0; i < 10; i++) {
+            assertThat(newBitSet.get(i)).isTrue();
+        }
+    }
+
+    @Test
+    public void givenBitSet_whenFlip_thenTogglesTrueToFalseAndViceVersa() {
+        BitSet bitSet = new BitSet();
+        bitSet.set(42);
+        bitSet.flip(42);
+        assertThat(bitSet.get(42)).isFalse();
+
+        bitSet.flip(12);
+        assertThat(bitSet.get(12)).isTrue();
+
+        bitSet.flip(30, 40);
+        for (int i = 30; i < 40; i++) {
+            assertThat(bitSet.get(i)).isTrue();
+        }
+    }
+
+    @Test
+    public void givenBitSet_whenGettingTheSize_thenReturnsTheSize() {
+        BitSet defaultBitSet = new BitSet();
+        assertThat(defaultBitSet.size()).isEqualTo(64);
+
+        BitSet bitSet = new BitSet(1024);
+        assertThat(bitSet.size()).isEqualTo(1024);
+
+        assertThat(bitSet.cardinality()).isEqualTo(0);
+        bitSet.set(10, 30);
+        assertThat(bitSet.cardinality()).isEqualTo(30 - 10);
+
+        assertThat(bitSet.length()).isEqualTo(30);
+        bitSet.set(100);
+        assertThat(bitSet.length()).isEqualTo(101);
+
+        assertThat(bitSet.isEmpty()).isFalse();
+        bitSet.clear();
+        assertThat(bitSet.isEmpty()).isTrue();
+    }
+
+    @Test
+    public void givenBitSet_whenSetOperations_thenShouldReturnAnotherBitSet() {
+        BitSet first = new BitSet();
+        first.set(5, 10);
+
+        BitSet second = new BitSet();
+        second.set(7, 15);
+
+        assertThat(first.intersects(second)).isTrue();
+
+        first.and(second);
+        assertThat(first.get(7)).isTrue();
+        assertThat(first.get(8)).isTrue();
+        assertThat(first.get(9)).isTrue();
+        assertThat(first.get(10)).isFalse();
+
+        first.clear();
+        first.set(5, 10);
+
+        first.xor(second);
+        for (int i = 5; i < 7; i++) {
+            assertThat(first.get(i)).isTrue();
+        }
+        for (int i = 10; i < 15; i++) {
+            assertThat(first.get(i)).isTrue();
+        }
+    }
+
+    @Test
+    public void givenBitSet_whenStream_thenStreamsAllSetBits() {
+        BitSet bitSet = new BitSet();
+        bitSet.set(15, 25);
+
+        bitSet.stream().forEach(System.out::println);
+        assertThat(bitSet.stream().count()).isEqualTo(10);
+    }
+
+    @Test
+    public void givenBitSet_whenNextOrPrev_thenReturnsTheNextOrPrevClearOrSetBit() {
+        BitSet bitSet = new BitSet();
+        bitSet.set(15, 25);
+
+        assertThat(bitSet.nextSetBit(13)).isEqualTo(15);
+        assertThat(bitSet.nextSetBit(25)).isEqualTo(-1);
+
+        assertThat(bitSet.nextClearBit(23)).isEqualTo(25);
+
+        assertThat(bitSet.previousClearBit(24)).isEqualTo(14);
+        assertThat(bitSet.previousSetBit(29)).isEqualTo(24);
+        assertThat(bitSet.previousSetBit(14)).isEqualTo(-1);
+    }
+}

core-java-modules/core-java-collections-list-3/README.md

@@ -10,4 +10,5 @@ This module contains articles about the Java List collection
 - [Performance Comparison of Primitive Lists in Java](https://www.baeldung.com/java-list-primitive-performance)
 - [Filtering a Java Collection by a List](https://www.baeldung.com/java-filter-collection-by-list)
 - [How to Count Duplicate Elements in Arraylist](https://www.baeldung.com/java-count-duplicate-elements-arraylist)
+- [Finding the Differences Between Two Lists in Java](https://www.baeldung.com/java-lists-difference)
 - [[<-- Prev]](/core-java-modules/core-java-collections-list-2)

core-java-modules/core-java-collections-list-3/pom.xml

@@ -21,6 +21,12 @@
             <artifactId>commons-collections4</artifactId>
             <version>${commons-collections4.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+            <scope>compile</scope>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>

core-java-modules/core-java-collections-list-3/src/test/java/com/baeldung/list/difference/FindDifferencesBetweenListsUnitTest.java

@@ -0,0 +1,96 @@
+package com.baeldung.list.difference;
+
+import com.google.common.collect.Sets;
+import org.apache.commons.collections4.CollectionUtils;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.assertj.core.api.Assertions.*;
+
+public class FindDifferencesBetweenListsUnitTest {
+
+    private static final List<String> listOne = Arrays.asList("Jack", "Tom", "Sam", "John", "James", "Jack");
+    private static final List<String> listTwo = Arrays.asList("Jack", "Daniel", "Sam", "Alan", "James", "George");
+
+    @Test
+    public void givenLists_whenUsingPlainJavaImpl_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>(listOne);
+        differences.removeAll(listTwo);
+        assertEquals(2, differences.size());
+        assertThat(differences).containsExactly("Tom", "John");
+    }
+
+    @Test
+    public void givenReverseLists_whenUsingPlainJavaImpl_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>(listTwo);
+        differences.removeAll(listOne);
+        assertEquals(3, differences.size());
+        assertThat(differences).containsExactly("Daniel", "Alan", "George");
+    }
+
+    @Test
+    public void givenLists_whenUsingJavaStreams_thenDifferencesAreFound() {
+        List<String> differences = listOne.stream()
+                .filter(element -> !listTwo.contains(element))
+                .collect(Collectors.toList());
+        assertEquals(2, differences.size());
+        assertThat(differences).containsExactly("Tom", "John");
+    }
+
+    @Test
+    public void givenReverseLists_whenUsingJavaStreams_thenDifferencesAreFound() {
+        List<String> differences = listTwo.stream()
+                .filter(element -> !listOne.contains(element))
+                .collect(Collectors.toList());
+        assertEquals(3, differences.size());
+        assertThat(differences).containsExactly("Daniel", "Alan", "George");
+    }
+
+    @Test
+    public void givenLists_whenUsingGoogleGuava_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>(Sets.difference(Sets.newHashSet(listOne), Sets.newHashSet(listTwo)));
+        assertEquals(2, differences.size());
+        assertThat(differences).containsExactlyInAnyOrder("Tom", "John");
+    }
+
+    @Test
+    public void givenReverseLists_whenUsingGoogleGuava_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>(Sets.difference(Sets.newHashSet(listTwo), Sets.newHashSet(listOne)));
+        assertEquals(3, differences.size());
+        assertThat(differences).containsExactlyInAnyOrder("Daniel", "Alan", "George");
+    }
+
+    @Test
+    public void givenLists_whenUsingApacheCommons_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>((CollectionUtils.removeAll(listOne, listTwo)));
+        assertEquals(2, differences.size());
+        assertThat(differences).containsExactly("Tom", "John");
+    }
+
+    @Test
+    public void givenReverseLists_whenUsingApacheCommons_thenDifferencesAreFound() {
+        List<String> differences = new ArrayList<>((CollectionUtils.removeAll(listTwo, listOne)));
+        assertEquals(3, differences.size());
+        assertThat(differences).containsExactly("Daniel", "Alan", "George");
+    }
+
+    @Test
+    public void givenLists_whenUsingPlainJavaImpl_thenDifferencesWithDuplicatesAreFound() {
+        List<String> differences = new ArrayList<>(listOne);
+        listTwo.forEach(differences::remove);
+        assertThat(differences).containsExactly("Tom", "John", "Jack");
+    }
+
+    @Test
+    public void givenLists_whenUsingApacheCommons_thenDifferencesWithDuplicatesAreFound() {
+        List<String> differences = new ArrayList<>(CollectionUtils.subtract(listOne, listTwo));
+        assertEquals(3, differences.size());
+        assertThat(differences).containsExactly("Tom", "John", "Jack");
+    }
+
+}

core-java-modules/core-java-collections-maps-2/pom.xml

@@ -21,20 +21,15 @@
             <version>${eclipse-collections.version}</version>
         </dependency>
         <dependency>
-            <groupId>net.sf.trove4j</groupId>
+            <groupId>com.carrotsearch</groupId>
-            <artifactId>trove4j</artifactId>
+            <artifactId>hppc</artifactId>
-            <version>${trove4j.version}</version>
+            <version>${hppc.version}</version>
         </dependency>
         <dependency>
             <groupId>it.unimi.dsi</groupId>
             <artifactId>fastutil</artifactId>
             <version>${fastutil.version}</version>
         </dependency>
-        <dependency>
-            <groupId>colt</groupId>
-            <artifactId>colt</artifactId>
-            <version>${colt.version}</version>
-        </dependency>
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
@@ -69,9 +64,8 @@
         <commons-collections4.version>4.1</commons-collections4.version>
         <avaitility.version>1.7.0</avaitility.version>
         <eclipse-collections.version>8.2.0</eclipse-collections.version>
-        <trove4j.version>3.0.2</trove4j.version>
+        <hppc.version>0.7.2</hppc.version>
         <fastutil.version>8.1.0</fastutil.version>
-        <colt.version>1.2.0</colt.version>
         <assertj.version>3.11.1</assertj.version>
     </properties>
 

core-java-modules/core-java-collections-maps-2/src/main/java/com/baeldung/map/primitives/PrimitiveMaps.java

@@ -1,29 +1,68 @@
 package com.baeldung.map.primitives;
 
-import cern.colt.map.AbstractIntDoubleMap;
+import com.carrotsearch.hppc.IntLongHashMap;
-import cern.colt.map.OpenIntDoubleHashMap;
+import com.carrotsearch.hppc.IntLongScatterMap;
-import gnu.trove.map.TDoubleIntMap;
+import com.carrotsearch.hppc.IntObjectHashMap;
-import gnu.trove.map.hash.TDoubleIntHashMap;
+import com.carrotsearch.hppc.IntObjectMap;
+import com.carrotsearch.hppc.IntObjectScatterMap;
+
 import it.unimi.dsi.fastutil.ints.Int2BooleanMap;
+import it.unimi.dsi.fastutil.ints.Int2BooleanMaps;
 import it.unimi.dsi.fastutil.ints.Int2BooleanOpenHashMap;
 import it.unimi.dsi.fastutil.ints.Int2BooleanSortedMap;
 import it.unimi.dsi.fastutil.ints.Int2BooleanSortedMaps;
+import it.unimi.dsi.fastutil.objects.ObjectIterator;
+
 import org.eclipse.collections.api.map.primitive.ImmutableIntIntMap;
 import org.eclipse.collections.api.map.primitive.MutableIntIntMap;
 import org.eclipse.collections.api.map.primitive.MutableObjectDoubleMap;
 import org.eclipse.collections.impl.factory.primitive.IntIntMaps;
 import org.eclipse.collections.impl.factory.primitive.ObjectDoubleMaps;
 
+import static java.lang.String.format;
+
+import java.math.BigDecimal;
+
 public class PrimitiveMaps {
 
     public static void main(String[] args) {
 
+        hppcMap();
         eclipseCollectionsMap();
-        troveMap();
-        coltMap();
         fastutilMap();
     }
 
+    private static void hppcMap() {
+        //Regular maps
+        IntLongHashMap intLongHashMap = new IntLongHashMap();
+        intLongHashMap.put(25,1L);
+        intLongHashMap.put(150,Long.MAX_VALUE);
+        intLongHashMap.put(1,0L);
+        
+        intLongHashMap.get(150);
+
+        IntObjectMap<BigDecimal> intObjectMap = new IntObjectHashMap<BigDecimal>();
+        intObjectMap.put(1, BigDecimal.valueOf(1));
+        intObjectMap.put(2, BigDecimal.valueOf(2500));
+
+        BigDecimal value = intObjectMap.get(2);
+
+        //Scatter maps
+        IntLongScatterMap intLongScatterMap = new IntLongScatterMap();
+        intLongScatterMap.put(1, 1L);
+        intLongScatterMap.put(2, -2L);
+        intLongScatterMap.put(1000,0L);    
+
+        intLongScatterMap.get(1000);
+
+        IntObjectScatterMap<BigDecimal> intObjectScatterMap = new IntObjectScatterMap<BigDecimal>();
+        intObjectScatterMap.put(1, BigDecimal.valueOf(1));
+        intObjectScatterMap.put(2, BigDecimal.valueOf(2500));
+
+        value = intObjectScatterMap.get(2);
+    }
+
+
     private static void fastutilMap() {
         Int2BooleanMap int2BooleanMap = new Int2BooleanOpenHashMap();
         int2BooleanMap.put(1, true);
@@ -32,13 +71,19 @@ public class PrimitiveMaps {
 
         boolean value = int2BooleanMap.get(1);
 
-        Int2BooleanSortedMap int2BooleanSorted = Int2BooleanSortedMaps.EMPTY_MAP;
+        //Lambda style iteration
-    }
+        Int2BooleanMaps.fastForEach(int2BooleanMap, entry -> {
+            System.out.println(String.format("Key: %d, Value: %b",entry.getIntKey(),entry.getBooleanValue()));
+        });
+
+        //Iterator based loop
+        ObjectIterator<Int2BooleanMap.Entry> iterator = Int2BooleanMaps.fastIterator(int2BooleanMap);
+        while(iterator.hasNext()) {
+            Int2BooleanMap.Entry entry = iterator.next();
+            System.out.println(String.format("Key: %d, Value: %b",entry.getIntKey(),entry.getBooleanValue()));
+
+        }
 
-    private static void coltMap() {
-        AbstractIntDoubleMap map = new OpenIntDoubleHashMap();
-        map.put(1, 4.5);
-        double value = map.get(1);
     }
 
     private static void eclipseCollectionsMap() {
@@ -53,17 +98,5 @@ public class PrimitiveMaps {
         dObject.addToValue("stability", 0.8);
     }
 
-    private static void troveMap() {
-        double[] doubles = new double[] {1.2, 4.5, 0.3};
-        int[] ints = new int[] {1, 4, 0};
 
-        TDoubleIntMap doubleIntMap = new TDoubleIntHashMap(doubles, ints);
-
-        doubleIntMap.put(1.2, 22);
-        doubleIntMap.put(4.5, 16);
-
-        doubleIntMap.adjustValue(1.2, 1);
-        doubleIntMap.adjustValue(4.5, 4);
-        doubleIntMap.adjustValue(0.3, 7);
-    }
 }

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -15,4 +15,5 @@ This module contains articles about advanced topics about multithreading with co
 - [The ABA Problem in Concurrency](https://www.baeldung.com/cs/aba-concurrency)
 - [Introduction to Lock-Free Data Structures](https://www.baeldung.com/lock-free-programming)
 - [Introduction to Exchanger in Java](https://www.baeldung.com/java-exchanger)
+- [Why Not To Start A Thread In The Constructor?](https://www.baeldung.com/java-thread-constructor)
 - [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-advanced-3/src/test/java/com/baeldung/workstealing/PrimeNumbersManualTest.java

@@ -15,7 +15,15 @@ import java.util.logging.Logger;
 
 import static org.junit.Assert.fail;
 
-public class PrimeNumbersUnitManualTest {
+/**
+ * This test expects the file target/test-classes/META-INF/BenchmarkList to be present.
+ *
+ * Before running the test ensure that the file is present. 
+ * If not, please run mvn install on the module.
+ * 
+ */
+
+public class PrimeNumbersManualTest {
 
     private static Logger logger = Logger.getAnonymousLogger();
 

core-java-modules/core-java-concurrency-advanced/src/main/java/com/baeldung/threadlocal/ThreadLocalAwareThreadPool.java

@@ -0,0 +1,25 @@
+package com.baeldung.threadlocal;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.RejectedExecutionHandler;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+public class ThreadLocalAwareThreadPool extends ThreadPoolExecutor {
+
+    public ThreadLocalAwareThreadPool(int corePoolSize,
+      int maximumPoolSize,
+      long keepAliveTime,
+      TimeUnit unit,
+      BlockingQueue<Runnable> workQueue,
+      ThreadFactory threadFactory,
+      RejectedExecutionHandler handler) {
+        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
+    }
+
+    @Override
+    protected void afterExecute(Runnable r, Throwable t) {
+        // Call remove on each ThreadLocal
+    }
+}

core-java-modules/core-java-concurrency-basic-2/README.md

@@ -3,10 +3,12 @@
 This module contains articles about basic Java concurrency
 
 ### Relevant Articles: 
+
 - [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)
 - [wait and notify() Methods in Java](https://www.baeldung.com/java-wait-notify)
 - [Difference Between Wait and Sleep in Java](https://www.baeldung.com/java-wait-and-sleep)
 - [Guide to the Synchronized Keyword in Java](https://www.baeldung.com/java-synchronized)
 - [Life Cycle of a Thread in Java](https://www.baeldung.com/java-thread-lifecycle)
 - [Guide to AtomicMarkableReference](https://www.baeldung.com/java-atomicmarkablereference)
+- [Why are Local Variables Thread-Safe in Java](https://www.baeldung.com/java-local-variables-thread-safe)
 - [[<-- Prev]](/core-java-modules/core-java-concurrency-basic)

core-java-modules/core-java-console/README.md

@@ -1,5 +1,8 @@
 #Core Java Console
 
-[Read and Write User Input in Java](http://www.baeldung.com/java-console-input-output)
+### Relevant Articles:
-[Formatting with printf() in Java](https://www.baeldung.com/java-printstream-printf)
+
-[ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)
+- [Read and Write User Input in Java](http://www.baeldung.com/java-console-input-output)
+- [Formatting with printf() in Java](https://www.baeldung.com/java-printstream-printf)
+- [ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)
+- [System.console() vs. System.out](https://www.baeldung.com/java-system-console-vs-system-out)

core-java-modules/core-java-console/src/main/java/com/baeldung/consoleout/ConsoleAndOut.java

@@ -0,0 +1,31 @@
+package com.baeldung.consoleout;
+
+import java.io.Console;
+
+public class ConsoleAndOut {
+    public static void main(String[] args) {
+        try {
+            printConsoleObject();
+            readPasswordFromConsole();
+        } catch (Exception ex) {
+            // Eating NullPointerExcpetion which will occur when this 
+            // program will be run from mediums other than console
+        }
+        printSysOut();    
+    }
+
+    static void printConsoleObject() {
+        Console console = System.console();
+        console.writer().print(console);
+    }
+
+    static void readPasswordFromConsole() {
+        Console console = System.console();
+        char[] password = console.readPassword("Enter password: ");
+        console.printf(String.valueOf(password));
+    }
+    
+    static void printSysOut() {
+        System.out.println(System.out);
+    }
+}

core-java-modules/core-java-console/src/test/java/com/baeldung/consoleout/ConsoleAndOutUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.consoleout;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+class ConsoleAndOutUnitTest {
+
+    @Test
+    void whenRetreivingConsole_thenPrintConsoleObject() {
+        assertThrows(NullPointerException.class, () -> {
+            ConsoleAndOut.printConsoleObject();  
+        });
+    }
+    
+    @Test
+    void whenReadingPassword_thenReadPassword() {
+        assertThrows(NullPointerException.class, () -> {
+            ConsoleAndOut.readPasswordFromConsole();  
+        });
+    }
+    
+    @Test
+    void whenRetrievingSysOut_thenPrintSysOutObject() {
+        ConsoleAndOut.printSysOut();
+    }
+}

core-java-modules/core-java-date-operations-2/README.md

@@ -2,6 +2,7 @@
 This module contains articles about date operations in Java.
 
 ### Relevant Articles:
+
 - [Get the Current Date Prior to Java 8](https://www.baeldung.com/java-get-the-current-date-legacy)
 - [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)
 - [Checking If Two Java Dates Are on the Same Day](https://www.baeldung.com/java-check-two-dates-on-same-day)
@@ -9,4 +10,5 @@ This module contains articles about date operations in Java.
 - [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [How to determine day of week by passing specific date in Java?](https://www.baeldung.com/java-get-day-of-week)
 - [Finding Leap Years in Java](https://www.baeldung.com/java-leap-year)
+- [Getting the Week Number From Any Date](https://www.baeldung.com/java-get-week-number)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

core-java-modules/core-java-exceptions-2/README.md

@@ -12,3 +12,5 @@ This module contains articles about core java exceptions
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Java Global Exception Handler](https://www.baeldung.com/java-global-exception-handler)
 - [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
+- [Java IOException “Too many open files”](https://www.baeldung.com/java-too-many-open-files)
+- [When Does Java Throw the ExceptionInInitializerError?](https://www.baeldung.com/java-exceptionininitializererror)

core-java-modules/core-java-exceptions-3/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [NoSuchMethodError in Java](https://www.baeldung.com/java-nosuchmethod-error)

core-java-modules/core-java-exceptions-3/pom.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung.exceptions</groupId>
+    <artifactId>core-java-exceptions-3</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-exceptions-3</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/nosuchmethoderror/MainMenu.java

@@ -0,0 +1,11 @@
+package com.baeldung.exceptions.nosuchmethoderror;
+
+public class MainMenu {
+    public static void main(String[] args) {
+        System.out.println("Today's Specials: " + getSpecials());
+    }
+
+    public static String getSpecials() {
+        return SpecialToday.getDesert();
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/nosuchmethoderror/SpecialToday.java

@@ -0,0 +1,8 @@
+package com.baeldung.exceptions.nosuchmethoderror;
+public class SpecialToday {
+    private static String desert = "Chocolate Cake";
+
+    public static String getDesert() {
+        return desert;
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/nosuchmethoderror/MainMenuUnitTest.java

@@ -0,0 +1,13 @@
+package com.baeldung.exceptions.nosuchmethoderror;
+
+import static org.junit.Assert.assertNotNull;
+
+import org.junit.jupiter.api.Test;
+
+class MainMenuUnitTest {
+
+    @Test
+    void whenGetSpecials_thenNotNull() {
+        assertNotNull(MainMenu.getSpecials());
+    }
+}

core-java-modules/core-java-io-3/.gitignore

@@ -0,0 +1,2 @@
+test-link*
+0.*

core-java-modules/core-java-io-3/README.md

@@ -3,5 +3,10 @@
 This module contains articles about core Java input and output (IO)
 
 ### Relevant Articles: 
+
 - [Java – Create a File](https://www.baeldung.com/java-how-to-create-a-file)
+- [Check If a Directory Is Empty in Java](https://www.baeldung.com/java-check-empty-directory)
+- [Check If a File or Directory Exists in Java](https://www.baeldung.com/java-file-directory-exists)
+- [Copy a Directory in Java](https://www.baeldung.com/java-copy-directory)
+- [Java Files Open Options](https://www.baeldung.com/java-file-options)
 - [[<-- Prev]](/core-java-modules/core-java-io-2)

core-java-modules/core-java-io-3/pom.xml

@@ -46,41 +46,14 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
-        <!-- https://mvnrepository.com/artifact/com.github.tomakehurst/wiremock -->
-        <dependency>
-            <groupId>com.github.tomakehurst</groupId>
-            <artifactId>wiremock</artifactId>
-            <version>${wiremock.version}</version>
-            <scope>test</scope>
-        </dependency>
 
     </dependencies>
 
     <build>
-        <finalName>core-java-io-3</finalName>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-javadoc-plugin</artifactId>
-                <version>${maven-javadoc-plugin.version}</version>
-                <configuration>
-                    <source>${maven.compiler.source}</source>
-                    <target>${maven.compiler.target}</target>
-                </configuration>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>
         <assertj.version>3.6.1</assertj.version>
-        <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
-        <wiremock.version>2.26.3</wiremock.version>
     </properties>
 
 </project>

core-java-modules/core-java-io-3/src/main/java/com/baeldung/copydirectory/ApacheCommons.java

@@ -0,0 +1,15 @@
+package com.baeldung.copydirectory;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.apache.commons.io.FileUtils;
+
+public class ApacheCommons {
+
+    public static void copyDirectory(String sourceDirectoryLocation, String destinationDirectoryLocation) throws IOException {
+        File sourceDirectory = new File(sourceDirectoryLocation);
+        File destinationDirectory = new File(destinationDirectoryLocation);
+        FileUtils.copyDirectory(sourceDirectory, destinationDirectory);
+    }
+}

core-java-modules/core-java-io-3/src/main/java/com/baeldung/copydirectory/CoreOld.java

@@ -0,0 +1,38 @@
+package com.baeldung.copydirectory;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+public class CoreOld {
+
+    public static void copyDirectoryJavaUnder7(File source, File destination) throws IOException {
+        if (source.isDirectory()) {
+            copyDirectory(source, destination);
+        } else {
+            copyFile(source, destination);
+        }
+    }
+
+    private static void copyDirectory(File sourceDirectory, File destinationDirectory) throws IOException {
+        if (!destinationDirectory.exists()) {
+            destinationDirectory.mkdir();
+        }
+        for (String f : sourceDirectory.list()) {
+            copyDirectoryJavaUnder7(new File(sourceDirectory, f), new File(destinationDirectory, f));
+        }
+    }
+
+    private static void copyFile(File sourceFile, File destinationFile) throws IOException {
+        try (InputStream in = new FileInputStream(sourceFile); OutputStream out = new FileOutputStream(destinationFile)) {
+            byte[] buf = new byte[1024];
+            int length;
+            while ((length = in.read(buf)) > 0) {
+                out.write(buf, 0, length);
+            }
+        }
+    }
+}

core-java-modules/core-java-io-3/src/main/java/com/baeldung/copydirectory/JavaNio.java

@@ -0,0 +1,22 @@
+package com.baeldung.copydirectory;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+public class JavaNio {
+
+    public static void copyDirectory(String sourceDirectoryLocation, String destinationDirectoryLocation) throws IOException {
+        Files.walk(Paths.get(sourceDirectoryLocation))
+          .forEach(source -> {
+              Path destination = Paths.get(destinationDirectoryLocation, source.toString()
+                .substring(sourceDirectoryLocation.length()));
+              try {
+                  Files.copy(source, destination);
+              } catch (IOException e) {
+                  e.printStackTrace();
+              }
+          });
+    }
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/copydirectory/ApacheCommonsUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.copydirectory;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Comparator;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class ApacheCommonsUnitTest {
+
+    private final String sourceDirectoryLocation = "src/test/resources/sourceDirectory3";
+    private final String subDirectoryName = "/childDirectory";
+    private final String fileName = "/file.txt";
+    private final String destinationDirectoryLocation = "src/test/resources/destinationDirectory3";
+
+    @BeforeEach
+    public void createDirectoryWithSubdirectoryAndFile() throws IOException {
+        Files.createDirectories(Paths.get(sourceDirectoryLocation));
+        Files.createDirectories(Paths.get(sourceDirectoryLocation + subDirectoryName));
+        Files.createFile(Paths.get(sourceDirectoryLocation + subDirectoryName + fileName));
+    }
+
+    @Test
+    public void whenSourceDirectoryExists_thenDirectoryIsFullyCopied() throws IOException {
+        ApacheCommons.copyDirectory(sourceDirectoryLocation, destinationDirectoryLocation);
+
+        assertTrue(new File(destinationDirectoryLocation).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName + fileName).exists());
+    }
+
+    @Test
+    public void whenSourceDirectoryDoesNotExist_thenExceptionIsThrown() {
+        assertThrows(Exception.class, () -> ApacheCommons.copyDirectory("nonExistingDirectory", destinationDirectoryLocation));
+    }
+
+    @AfterEach
+    public void cleanUp() throws IOException {
+        Files.walk(Paths.get(sourceDirectoryLocation))
+            .sorted(Comparator.reverseOrder())
+            .map(Path::toFile)
+            .forEach(File::delete);
+        if (new File(destinationDirectoryLocation).exists()) {
+            Files.walk(Paths.get(destinationDirectoryLocation))
+                .sorted(Comparator.reverseOrder())
+                .map(Path::toFile)
+                .forEach(File::delete);
+        }
+    }
+
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/copydirectory/CoreOldUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.copydirectory;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Comparator;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class CoreOldUnitTest {
+
+    private final String sourceDirectoryLocation = "src/test/resources/sourceDirectory1";
+    private final String subDirectoryName = "/childDirectory";
+    private final String fileName = "/file.txt";
+    private final String destinationDirectoryLocation = "src/test/resources/destinationDirectory1";
+
+    @BeforeEach
+    public void createDirectoryWithSubdirectoryAndFile() throws IOException {
+        Files.createDirectories(Paths.get(sourceDirectoryLocation));
+        Files.createDirectories(Paths.get(sourceDirectoryLocation + subDirectoryName));
+        Files.createFile(Paths.get(sourceDirectoryLocation + subDirectoryName + fileName));
+    }
+
+    @Test
+    public void whenSourceDirectoryExists_thenDirectoryIsFullyCopied() throws IOException {
+        File sourceDirectory = new File(sourceDirectoryLocation);
+        File destinationDirectory = new File(destinationDirectoryLocation);
+        CoreOld.copyDirectoryJavaUnder7(sourceDirectory, destinationDirectory);
+
+        assertTrue(new File(destinationDirectoryLocation).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName + fileName).exists());
+    }
+
+    @Test
+    public void whenSourceDirectoryDoesNotExist_thenExceptionIsThrown() throws IOException {
+        File sourceDirectory = new File("nonExistingDirectory");
+        File destinationDirectory = new File(destinationDirectoryLocation);
+        assertThrows(IOException.class, () -> CoreOld.copyDirectoryJavaUnder7(sourceDirectory, destinationDirectory));
+    }
+
+    @AfterEach
+    public void cleanUp() throws IOException {
+        Files.walk(Paths.get(sourceDirectoryLocation))
+            .sorted(Comparator.reverseOrder())
+            .map(Path::toFile)
+            .forEach(File::delete);
+        if (new File(destinationDirectoryLocation).exists()) {
+            Files.walk(Paths.get(destinationDirectoryLocation))
+                .sorted(Comparator.reverseOrder())
+                .map(Path::toFile)
+                .forEach(File::delete);
+        }
+    }
+
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/copydirectory/JavaNioUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.copydirectory;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Comparator;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class JavaNioUnitTest {
+
+    private final String sourceDirectoryLocation = "src/test/resources/sourceDirectory2";
+    private final String subDirectoryName = "/childDirectory";
+    private final String fileName = "/file.txt";
+    private final String destinationDirectoryLocation = "src/test/resources/destinationDirectory2";
+
+    @BeforeEach
+    public void createDirectoryWithSubdirectoryAndFile() throws IOException {
+        Files.createDirectories(Paths.get(sourceDirectoryLocation));
+        Files.createDirectories(Paths.get(sourceDirectoryLocation + subDirectoryName));
+        Files.createFile(Paths.get(sourceDirectoryLocation + subDirectoryName + fileName));
+    }
+
+    @Test
+    public void whenSourceDirectoryExists_thenDirectoryIsFullyCopied() throws IOException {
+        JavaNio.copyDirectory(sourceDirectoryLocation, destinationDirectoryLocation);
+
+        assertTrue(new File(destinationDirectoryLocation).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName).exists());
+        assertTrue(new File(destinationDirectoryLocation + subDirectoryName + fileName).exists());
+    }
+
+    @Test
+    public void whenSourceDirectoryDoesNotExist_thenExceptionIsThrown() {
+        assertThrows(IOException.class, () -> JavaNio.copyDirectory("nonExistingDirectory", destinationDirectoryLocation));
+    }
+
+    @AfterEach
+    public void cleanUp() throws IOException {
+        Files.walk(Paths.get(sourceDirectoryLocation))
+            .sorted(Comparator.reverseOrder())
+            .map(Path::toFile)
+            .forEach(File::delete);
+        if (new File(destinationDirectoryLocation).exists()) {
+            Files.walk(Paths.get(destinationDirectoryLocation))
+                .sorted(Comparator.reverseOrder())
+                .map(Path::toFile)
+                .forEach(File::delete);
+        }
+    }
+
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/emptiness/DirectoryEmptinessUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.emptiness;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DirectoryEmptinessUnitTest {
+
+    @Test
+    public void givenPath_whenInvalid_thenReturnsFalse() throws IOException {
+        assertThat(isEmpty(Paths.get("invalid-addr"))).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotDirectory_thenReturnsFalse() throws IOException {
+        Path aFile = Paths.get(getClass().getResource("/notDir.txt").getPath());
+        assertThat(isEmpty(aFile)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotEmptyDir_thenReturnsFalse() throws IOException {
+        Path currentDir = new File("").toPath().toAbsolutePath();
+        assertThat(isEmpty(currentDir)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenIsEmpty_thenReturnsTrue() throws Exception {
+        Path path = Files.createTempDirectory("baeldung-empty");
+        assertThat(isEmpty(path)).isTrue();
+    }
+
+    private static boolean isEmpty(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (DirectoryStream<Path> directory = Files.newDirectoryStream(path)) {
+                return !directory.iterator().hasNext();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmpty2(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (Stream<Path> entries = Files.list(path)) {
+                return !entries.findFirst().isPresent();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmptyInefficient(Path path) {
+        return path.toFile().listFiles().length == 0;
+    }
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/existence/ExistenceUnitTest.java

@@ -0,0 +1,91 @@
+package com.baeldung.existence;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.concurrent.ThreadLocalRandom;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class ExistenceUnitTest {
+
+    @Test
+    public void givenFile_whenDoesNotExist_thenFilesReturnsFalse() {
+        Path path = Paths.get("does-not-exist.txt");
+
+        assertFalse(Files.exists(path));
+        assertTrue(Files.notExists(path));
+    }
+
+    @Test
+    public void givenFile_whenExists_thenFilesShouldReturnTrue() throws IOException {
+        Path tempFile = Files.createTempFile("baeldung", "exist-nio");
+        assertTrue(Files.exists(tempFile));
+        assertFalse(Files.notExists(tempFile));
+
+        Path tempDirectory = Files.createTempDirectory("baeldung-exists");
+        assertTrue(Files.exists(tempDirectory));
+        assertFalse(Files.notExists(tempDirectory));
+
+        assertTrue(Files.isDirectory(tempDirectory));
+        assertFalse(Files.isDirectory(tempFile));
+        assertTrue(Files.isRegularFile(tempFile));
+
+        assertTrue(Files.isReadable(tempFile));
+
+        Files.deleteIfExists(tempFile);
+        Files.deleteIfExists(tempDirectory);
+    }
+
+    @Test
+    public void givenSymbolicLink_whenTargetDoesNotExists_thenFollowOrNotBasedOnTheOptions() throws IOException {
+        Path target = Files.createTempFile("baeldung", "target");
+        Path symbol = Paths.get("test-link-" + ThreadLocalRandom.current().nextInt());
+
+        Path symbolicLink = Files.createSymbolicLink(symbol, target);
+        assertTrue(Files.exists(symbolicLink));
+        assertTrue(Files.isSymbolicLink(symbolicLink));
+        assertFalse(Files.isSymbolicLink(target));
+
+        Files.deleteIfExists(target);
+        assertFalse(Files.exists(symbolicLink));
+        assertTrue(Files.exists(symbolicLink, LinkOption.NOFOLLOW_LINKS));
+
+        Files.deleteIfExists(symbolicLink);
+    }
+
+    @Test
+    public void givenFile_whenDoesNotExist_thenFileReturnsFalse() {
+        assertFalse(new File("invalid").exists());
+        assertFalse(new File("invalid").isFile());
+    }
+
+    @Test
+    public void givenFile_whenExist_thenShouldReturnTrue() throws IOException {
+        Path tempFilePath = Files.createTempFile("baeldung", "exist-io");
+        Path tempDirectoryPath = Files.createTempDirectory("baeldung-exists-io");
+
+        File tempFile = new File(tempFilePath.toString());
+        File tempDirectory = new File(tempDirectoryPath.toString());
+
+        assertTrue(tempFile.exists());
+        assertTrue(tempDirectory.exists());
+
+        assertTrue(tempFile.isFile());
+        assertFalse(tempDirectory.isFile());
+
+        assertTrue(tempDirectory.isDirectory());
+        assertFalse(tempFile.isDirectory());
+
+        assertTrue(tempFile.canRead());
+
+        Files.deleteIfExists(tempFilePath);
+        Files.deleteIfExists(tempDirectoryPath);
+    }
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/openoptions/OpenOptionsUnitTest.java

@@ -0,0 +1,96 @@
+package com.baeldung.openoptions;
+
+import org.hamcrest.CoreMatchers;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.*;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+
+import static org.junit.Assert.*;
+
+public class OpenOptionsUnitTest {
+
+    private static final String HOME = System.getProperty("user.home");
+    private static final String DUMMY_FILE_NAME = "sample.txt";
+    private static final String EXISTING_FILE_NAME = "existingFile.txt";
+
+    private static final String DUMMY_TEXT = "This is a sample text.";
+    private static final String ANOTHER_DUMMY_TEXT = "This is a another text.";
+
+    @BeforeClass
+    public static void beforeAll() throws IOException {
+        Path path = Paths.get(HOME, DUMMY_FILE_NAME);
+
+        try (OutputStream out = Files.newOutputStream(path)) {
+            out.write(DUMMY_TEXT.getBytes());
+        }
+
+        Files.createFile(Paths.get(HOME, EXISTING_FILE_NAME));
+    }
+
+    @AfterClass
+    public static void afterAll() throws IOException {
+        Files.delete(Paths.get(HOME, "newfile.txt"));
+        Files.delete(Paths.get(HOME, "sparse.txt"));
+        Files.delete(Paths.get(HOME, DUMMY_FILE_NAME));
+    }
+
+    @Test
+    public void givenExistingPath_whenCreateNewFile_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, "newfile.txt");
+        assertFalse(Files.exists(path));
+
+        Files.write(path, DUMMY_TEXT.getBytes(), StandardOpenOption.CREATE);
+        assertTrue(Files.exists(path));
+    }
+
+    @Test
+    public void givenExistingPath_whenReadExistingFile_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, DUMMY_FILE_NAME);
+
+        try (InputStream in = Files.newInputStream(path); BufferedReader reader = new BufferedReader(new InputStreamReader(in))) {
+            String line;
+            while ((line = reader.readLine()) != null) {
+                assertThat(line, CoreMatchers.containsString(DUMMY_TEXT));
+            }
+        }
+    }
+
+    @Test
+    public void givenExistingPath_whenWriteToExistingFile_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, DUMMY_FILE_NAME);
+
+        try (OutputStream out = Files.newOutputStream(path, StandardOpenOption.APPEND, StandardOpenOption.WRITE)) {
+            out.write(ANOTHER_DUMMY_TEXT.getBytes());
+        }
+    }
+
+    @Test
+    public void givenExistingPath_whenCreateSparseFile_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, "sparse.txt");
+        Files.write(path, DUMMY_TEXT.getBytes(), StandardOpenOption.CREATE_NEW, StandardOpenOption.SPARSE);
+    }
+
+    @Test
+    public void givenExistingPath_whenDeleteOnClose_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, EXISTING_FILE_NAME);
+        assertTrue(Files.exists(path)); // file was already created and exists
+
+        try (OutputStream out = Files.newOutputStream(path, StandardOpenOption.APPEND, StandardOpenOption.WRITE, StandardOpenOption.DELETE_ON_CLOSE)) {
+            out.write(ANOTHER_DUMMY_TEXT.getBytes());
+        }
+
+        assertFalse(Files.exists(path)); // file is deleted
+    }
+
+    @Test
+    public void givenExistingPath_whenWriteAndSync_thenCorrect() throws IOException {
+        Path path = Paths.get(HOME, DUMMY_FILE_NAME);
+        Files.write(path, ANOTHER_DUMMY_TEXT.getBytes(), StandardOpenOption.APPEND, StandardOpenOption.WRITE, StandardOpenOption.SYNC);
+    }
+}

core-java-modules/core-java-io-apis/README.md

@@ -7,7 +7,6 @@ This module contains articles about core Java input/output(IO) APIs.
 - [A Guide to the Java FileReader Class](https://www.baeldung.com/java-filereader)
 - [The Java File Class](https://www.baeldung.com/java-io-file)
 - [Java FileWriter](https://www.baeldung.com/java-filewriter)
-- [Differences Between the Java WatchService API and the Apache Commons IO Monitor Library](https://www.baeldung.com/java-watchservice-vs-apache-commons-io-monitor-library)
 - [Comparing getPath(), getAbsolutePath(), and getCanonicalPath() in Java](https://www.baeldung.com/java-path)
 - [Quick Use of FilenameFilter](https://www.baeldung.com/java-filename-filter)
 - [Guide to BufferedReader](https://www.baeldung.com/java-buffered-reader)

core-java-modules/core-java-jvm-2/README.md

@@ -8,4 +8,7 @@ This module contains articles about working with the Java Virtual Machine (JVM).
 - [Measuring Object Sizes in the JVM](https://www.baeldung.com/jvm-measuring-object-sizes)
 - [Adding Shutdown Hooks for JVM Applications](https://www.baeldung.com/jvm-shutdown-hooks)
 - [boolean and boolean[] Memory Layout in the JVM](https://www.baeldung.com/jvm-boolean-memory-layout)
-- More articles: [[<-- prev]](/core-java-modules/core-java-jvm)
+- [Where Is the Array Length Stored in JVM?](https://www.baeldung.com/java-jvm-array-length)
+- [Memory Address of Objects in Java](https://www.baeldung.com/java-object-memory-address)
+- [List All Classes Loaded in a Specific Class Loader](https://www.baeldung.com/java-list-classes-class-loader)
+- More articles: [[<-- prev]](/core-java-modules/core-java-jvm)

core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/Launcher.java

@@ -0,0 +1,19 @@
+package com.baeldung.loadedclasslisting;
+
+import java.util.Arrays;
+
+public class Launcher {
+
+    public static void main(String[] args) {
+        printClassesLoadedBy("BOOTSTRAP");
+        printClassesLoadedBy("SYSTEM");
+        printClassesLoadedBy("EXTENSION");
+    }
+
+    private static void printClassesLoadedBy(String classLoaderType) {
+        System.out.println(classLoaderType + " ClassLoader : ");
+        Class<?>[] classes = ListLoadedClassesAgent.listLoadedClasses(classLoaderType);
+        Arrays.asList(classes)
+            .forEach(clazz -> System.out.println(clazz.getCanonicalName()));
+    }
+}

core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/ListLoadedClassesAgent.java

@@ -0,0 +1,40 @@
+package com.baeldung.loadedclasslisting;
+
+import java.lang.instrument.Instrumentation;
+
+public class ListLoadedClassesAgent {
+
+    private static Instrumentation instrumentation;
+
+    public static void premain(String agentArgs, Instrumentation instrumentation) {
+        ListLoadedClassesAgent.instrumentation = instrumentation;
+    }
+
+    public static Class<?>[] listLoadedClasses(String classLoaderType) {
+        if (instrumentation == null) {
+            throw new IllegalStateException(
+              "ListLoadedClassesAgent is not initialized.");
+        }
+        return instrumentation.getInitiatedClasses(
+          getClassLoader(classLoaderType));
+    }
+
+    private static ClassLoader getClassLoader(String classLoaderType) {
+        ClassLoader classLoader = null;
+        switch (classLoaderType) {
+        case "SYSTEM":
+            classLoader = ClassLoader.getSystemClassLoader();
+            break;
+        case "EXTENSION":
+            classLoader = ClassLoader.getSystemClassLoader().getParent();
+            break;
+        // passing a null value to the Instrumentation : getInitiatedClasses method
+        // defaults to the bootstrap class loader
+        case "BOOTSTRAP":
+            break;
+        default:
+            break;
+        }
+        return classLoader;
+    }
+}

core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/MANIFEST.MF

@@ -0,0 +1 @@
+Premain-Class: com.baeldung.loadedclasslisting.ListLoadedClassesAgent

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/entity/Human.java

@@ -37,7 +37,7 @@ public class Human {
 
     public static int compareByNameThenAge(final Human lhs, final Human rhs) {
         if (lhs.name.equals(rhs.name)) {
-            return lhs.age - rhs.age;
+            return Integer.compare(lhs.age, rhs.age);
         } else {
             return lhs.name.compareTo(rhs.name);
         }

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/lambda/tips/Bar.java

@@ -6,8 +6,11 @@ public interface Bar {
 
     String method(String string);
 
-    default String defaultMethod() {
+    default String defaultBar() {
-        return "String from Bar";
+        return "Default String from Bar";
     }
 
+    default String defaultCommon() {
+        return "Default Common from Bar";
+    }
 }

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/lambda/tips/Baz.java

@@ -6,7 +6,11 @@ public interface Baz {
 
     String method(String string);
 
-    default String defaultMethod() {
+    default String defaultBaz() {
-        return "String from Baz";
+        return "Default String from Baz";
+    }
+
+    default String defaultCommon(){
+        return "Default Common from Baz";
     }
 }

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/lambda/tips/FooExtended.java

@@ -5,8 +5,7 @@ package com.baeldung.java8.lambda.tips;
 public interface FooExtended extends Baz, Bar {
 
     @Override
-    default String defaultMethod() {
+    default String defaultCommon() {
-        return Bar.super.defaultMethod();
+        return Bar.super.defaultCommon();
     }
-
 }

core-java-modules/core-java-lambdas/src/test/java/com/baeldung/java8/Java8SortUnitTest.java

@@ -54,7 +54,7 @@ public class Java8SortUnitTest {
         final List<Human> humans = Lists.newArrayList(new Human("Sarah", 12), new Human("Sarah", 10), new Human("Zack", 12));
         humans.sort((lhs, rhs) -> {
             if (lhs.getName().equals(rhs.getName())) {
-                return lhs.getAge() - rhs.getAge();
+                return Integer.compare(lhs.getAge(), rhs.getAge());
             } else {
                 return lhs.getName().compareTo(rhs.getName());
             }

core-java-modules/core-java-lambdas/src/test/java/com/baeldung/java8/lambda/tips/Java8FunctionalInteracesLambdasUnitTest.java

@@ -39,9 +39,9 @@ public class Java8FunctionalInteracesLambdasUnitTest {
     @Test
     public void defaultMethodFromExtendedInterface_whenReturnDefiniteString_thenCorrect() {
         final FooExtended fooExtended = string -> string;
-        final String result = fooExtended.defaultMethod();
+        final String result = fooExtended.defaultCommon();
 
-        assertEquals("String from Bar", result);
+        assertEquals("Default Common from Bar", result);
     }
 
     @Test

core-java-modules/core-java-lang-3/README.md

@@ -2,4 +2,7 @@
 
 This module contains articles about core features in the Java language
 
+- [Class.isInstance vs Class.isAssignableFrom](https://www.baeldung.com/java-isinstance-isassignablefrom)
+- [Converting a Java String Into a Boolean](https://www.baeldung.com/java-string-to-boolean)
+- [When are Static Variables Initialized in Java?](https://www.baeldung.com/java-static-variables-initialization)
 - [[<-- Prev]](/core-java-modules/core-java-lang-2)

core-java-modules/core-java-lang-oop-methods/README.md

@@ -3,7 +3,9 @@
 This module contains articles about methods in Java
 
 ### Relevant Articles: 
+
 - [Methods in Java](https://www.baeldung.com/java-methods)
 - [Method Overloading and Overriding in Java](https://www.baeldung.com/java-method-overload-override)
 - [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
 - [Guide to hashCode() in Java](https://www.baeldung.com/java-hashcode)
+- [The Covariant Return Type in Java](https://www.baeldung.com/java-covariant-return-type)

core-java-modules/core-java-lang-oop-types/README.md

@@ -3,6 +3,7 @@
 This module contains articles about types in Java
 
 ### Relevant Articles: 
+
 - [Java Classes and Objects](https://www.baeldung.com/java-classes-objects)
 - [Guide to the this Java Keyword](https://www.baeldung.com/java-this)
 - [Nested Classes in Java](https://www.baeldung.com/java-nested-classes)
@@ -10,3 +11,4 @@ This module contains articles about types in Java
 - [Iterating Over Enum Values in Java](https://www.baeldung.com/java-enum-iteration)
 - [Attaching Values to Java Enum](https://www.baeldung.com/java-enum-values)
 - [A Guide to Java Enums](https://www.baeldung.com/a-guide-to-java-enums)
+- [Determine if an Object is of Primitive Type](https://www.baeldung.com/java-object-primitive-type)

core-java-modules/core-java-lang-oop-types/pom.xml

@@ -12,4 +12,12 @@
     <artifactId>core-java-lang-oop-types</artifactId>
     <name>core-java-lang-oop-types</name>
     <packaging>jar</packaging>
+    
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+    </dependencies>
 </project>

core-java-modules/core-java-lang-oop-types/src/main/java/com/baeldung/primitivetype/PrimitiveTypeUtil.java

@@ -0,0 +1,26 @@
+package com.baeldung.primitivetype;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class PrimitiveTypeUtil {
+
+    private static final Map<Class<?>, Class<?>> WRAPPER_TYPE_MAP;
+    static {
+        WRAPPER_TYPE_MAP = new HashMap<Class<?>, Class<?>>(16);
+        WRAPPER_TYPE_MAP.put(Integer.class, int.class);
+        WRAPPER_TYPE_MAP.put(Byte.class, byte.class);
+        WRAPPER_TYPE_MAP.put(Character.class, char.class);
+        WRAPPER_TYPE_MAP.put(Boolean.class, boolean.class);
+        WRAPPER_TYPE_MAP.put(Double.class, double.class);
+        WRAPPER_TYPE_MAP.put(Float.class, float.class);
+        WRAPPER_TYPE_MAP.put(Long.class, long.class);
+        WRAPPER_TYPE_MAP.put(Short.class, short.class);
+        WRAPPER_TYPE_MAP.put(Void.class, void.class);
+    }
+
+    public static boolean isPrimitiveType(Object source) {
+        return WRAPPER_TYPE_MAP.containsKey(source.getClass());
+    }
+
+}

core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/primitivetype/PrimitiveTypeUnitTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.primitivetype;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.commons.lang3.ClassUtils;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import com.google.common.primitives.Primitives;
+
+public class PrimitiveTypeUnitTest {
+
+    @Test
+    public void givenAClass_whenCheckWithPrimitiveTypeUtil_thenShouldValidate() {
+        assertTrue(PrimitiveTypeUtil.isPrimitiveType(false));
+        assertTrue(PrimitiveTypeUtil.isPrimitiveType(1L));
+        assertFalse(PrimitiveTypeUtil.isPrimitiveType(StringUtils.EMPTY));
+    }
+
+    @Test
+    public void givenAClass_whenCheckWithCommonsLang_thenShouldValidate() {
+        assertTrue(ClassUtils.isPrimitiveOrWrapper(Boolean.FALSE.getClass()));
+        assertTrue(ClassUtils.isPrimitiveOrWrapper(boolean.class));
+        assertFalse(ClassUtils.isPrimitiveOrWrapper(StringUtils.EMPTY.getClass()));
+    }
+
+    @Test
+    public void givenAClass_whenCheckWithGuava_thenShouldValidate() {
+        assertTrue(Primitives.isWrapperType(Boolean.FALSE.getClass()));
+        assertFalse(Primitives.isWrapperType(StringUtils.EMPTY.getClass()));
+        assertFalse(Primitives.isWrapperType(Boolean.TYPE.getClass()));
+    }
+}

core-java-modules/core-java-lang/src/main/java/com/baeldung/comparable/Player.java

@@ -45,7 +45,7 @@ public class Player implements Comparable<Player> {
 
     @Override
     public int compareTo(Player otherPlayer) {
-        return (this.getRanking() - otherPlayer.getRanking());
+        return Integer.compare(getRanking(), otherPlayer.getRanking());
     }
 
 }

core-java-modules/core-java-lang/src/main/java/com/baeldung/comparator/PlayerAgeComparator.java

@@ -6,7 +6,7 @@ public class PlayerAgeComparator implements Comparator<Player> {
 
     @Override
     public int compare(Player firstPlayer, Player secondPlayer) {
-       return (firstPlayer.getAge() - secondPlayer.getAge());
+       return Integer.compare(firstPlayer.getAge(), secondPlayer.getAge());
     }
 
 }

core-java-modules/core-java-lang/src/main/java/com/baeldung/comparator/PlayerRankingComparator.java

@@ -6,7 +6,7 @@ public class PlayerRankingComparator implements Comparator<Player> {
 
     @Override
     public int compare(Player firstPlayer, Player secondPlayer) {
-       return (firstPlayer.getRanking() - secondPlayer.getRanking());
+       return Integer.compare(firstPlayer.getRanking(), secondPlayer.getRanking());
     }
 
 }

core-java-modules/core-java-lang/src/test/java/com/baeldung/comparator/AvoidingSubtractionUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.comparator;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class AvoidingSubtractionUnitTest {
+
+    @Test
+    public void givenTwoPlayers_whenUsingSubtraction_thenOverflow() {
+        Comparator<Player> comparator = (p1, p2) -> p1.getRanking() - p2.getRanking();
+        Player player1 = new Player(59, "John", Integer.MAX_VALUE);
+        Player player2 = new Player(67, "Roger", -1);
+
+        List<Player> players = Arrays.asList(player1, player2);
+        players.sort(comparator);
+        System.out.println(players);
+
+        assertEquals("John", players.get(0).getName());
+        assertEquals("Roger", players.get(1).getName());
+    }
+}

core-java-modules/core-java-lang/src/test/java/com/baeldung/comparator/Java8ComparatorUnitTest.java

@@ -1,14 +1,14 @@
 package com.baeldung.comparator;
 
-import static org.junit.Assert.assertEquals;
+import org.junit.Before;
+import org.junit.Test;
 
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
 
-import org.junit.Before;
+import static org.junit.Assert.assertEquals;
-import org.junit.Test;
 
 public class Java8ComparatorUnitTest {
 
@@ -28,7 +28,7 @@ public class Java8ComparatorUnitTest {
     @Test
     public void whenComparing_UsingLambda_thenSorted() {
         System.out.println("************** Java 8 Comaparator **************");
-        Comparator<Player> byRanking = (Player player1, Player player2) -> player1.getRanking() - player2.getRanking();
+        Comparator<Player> byRanking = (Player player1, Player player2) -> Integer.compare(player1.getRanking(), player2.getRanking());
 
         System.out.println("Before Sorting : " + footballTeam);
         Collections.sort(footballTeam, byRanking);

core-java-modules/core-java-networking-2/README.md

@@ -12,4 +12,5 @@ This module contains articles about networking in Java
 - [Authentication with HttpUrlConnection](https://www.baeldung.com/java-http-url-connection)
 - [Download a File from an URL in Java](https://www.baeldung.com/java-download-file)
 - [Handling java.net.ConnectException](https://www.baeldung.com/java-net-connectexception)
+- [Getting MAC addresses in Java](https://www.baeldung.com/java-mac-address)
 - [[<-- Prev]](/core-java-modules/core-java-networking)

core-java-modules/core-java-nio-2/src/main/java/com/baeldung/selector/EchoServer.java

@@ -49,11 +49,11 @@ public class EchoServer {
         if (new String(buffer.array()).trim().equals(POISON_PILL)) {
             client.close();
             System.out.println("Not accepting client messages anymore");
+        } else {
+            buffer.flip();
+            client.write(buffer);
+            buffer.clear();
         }
-
-        buffer.flip();
-        client.write(buffer);
-        buffer.clear();
     }
 
     private static void register(Selector selector, ServerSocketChannel serverSocket) throws IOException {

core-java-modules/core-java-os/README.md

@@ -12,5 +12,6 @@ This module contains articles about working with the operating system (OS) in Ja
 - [How to Print Screen in Java](http://www.baeldung.com/print-screen-in-java)
 - [Pattern Search with Grep in Java](http://www.baeldung.com/grep-in-java)
 - [How to Run a Shell Command in Java](http://www.baeldung.com/run-shell-command-in-java)
+- [Taking Screenshots Using Java](https://www.baeldung.com/java-taking-screenshots)
 
-This module uses Java 9, so make sure to have the JDK 9 installed to run it.
+This module uses Java 9, so make sure to have the JDK 9 installed to run it.

core-java-modules/core-java-os/src/test/java/com/baeldung/screenshot/ScreenshotUnitTest.java

@@ -0,0 +1,51 @@
+import javax.imageio.ImageIO;
+import java.awt.Component;
+import java.awt.GraphicsDevice;
+import java.awt.GraphicsEnvironment;
+import java.awt.Rectangle;
+import java.awt.Robot;
+import java.awt.Toolkit;
+import java.awt.image.BufferedImage;
+import java.io.File;
+import org.junit.Test;
+
+import static org.junit.Assert.assertTrue;
+
+public class ScreenshotUnitTest {
+
+    @Test
+    public void givenMainScreen_whenTakeScreenshot_thenSaveToFile() throws Exception {
+        Rectangle screenRect = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
+        BufferedImage capture = new Robot().createScreenCapture(screenRect);
+        File imageFile = File.createTempFile("single-screen", "bmp");
+        ImageIO.write(capture, "bmp", imageFile);
+        assertTrue(imageFile.exists());
+    }
+
+    @Test
+    public void givenMultipleScreens_whenTakeScreenshot_thenSaveToFile() throws Exception {
+        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
+        GraphicsDevice[] screens = ge.getScreenDevices();
+        Rectangle allScreenBounds = new Rectangle();
+        for (GraphicsDevice screen : screens) {
+            Rectangle screenBounds = screen.getDefaultConfiguration().getBounds();
+            allScreenBounds.width += screenBounds.width;
+            allScreenBounds.height = Math.max(allScreenBounds.height, screenBounds.height);
+        }
+        BufferedImage capture = new Robot().createScreenCapture(allScreenBounds);
+        File imageFile = File.createTempFile("all-screens", "bmp");
+        ImageIO.write(capture, "bmp", imageFile);
+        assertTrue(imageFile.exists());
+    }
+
+    @Test
+    public void givenComponent_whenTakeScreenshot_thenSaveToFile(Component component) throws Exception {
+        Rectangle componentRect = component.getBounds();
+        BufferedImage bufferedImage = new BufferedImage(componentRect.width, componentRect.height, BufferedImage.TYPE_INT_ARGB);
+        component.paint(bufferedImage.getGraphics());
+        File imageFile = File.createTempFile("component-screenshot", "bmp");
+        ImageIO.write(bufferedImage, "bmp", imageFile);
+        assertTrue(imageFile.exists());
+    }
+
+}

core-java-modules/core-java-reflection-2/README.md

@@ -0,0 +1,4 @@
+### Relevant Articles:
+
+- [Reading the Value of ‘private’ Fields from a Different Class in Java](https://www.baeldung.com/java-reflection-read-private-field-value)
+- [Set Field Value With Reflection](https://www.baeldung.com/java-set-private-field-value)

core-java-modules/core-java-reflection-2/src/test/java/com/baeldung/reflection/set/fields/SetFieldsUsingReflectionUnitTest.java

@@ -0,0 +1,183 @@
+package com.baeldung.reflection.set.fields;
+
+import java.lang.reflect.Field;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.reflection.access.privatefields.Person;
+
+public class SetFieldsUsingReflectionUnitTest {
+
+    @Test
+    public void whenSetIntegerFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field ageField = person.getClass()
+            .getDeclaredField("age");
+        ageField.setAccessible(true);
+
+        byte age = 26;
+        ageField.setByte(person, age);
+        Assertions.assertEquals(age, person.getAge());
+
+        Field uidNumberField = person.getClass()
+            .getDeclaredField("uidNumber");
+        uidNumberField.setAccessible(true);
+
+        short uidNumber = 5555;
+        uidNumberField.setShort(person, uidNumber);
+        Assertions.assertEquals(uidNumber, person.getUidNumber());
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        int pinCode = 411057;
+        pinCodeField.setInt(person, pinCode);
+        Assertions.assertEquals(pinCode, person.getPinCode());
+
+        Field contactNumberField = person.getClass()
+            .getDeclaredField("contactNumber");
+        contactNumberField.setAccessible(true);
+
+        long contactNumber = 123456789L;
+        contactNumberField.setLong(person, contactNumber);
+        Assertions.assertEquals(contactNumber, person.getContactNumber());
+
+    }
+
+    @Test
+    public void whenDoUnboxing_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        Integer pinCode = 411057;
+        pinCodeField.setInt(person, pinCode);
+        Assertions.assertEquals(pinCode, person.getPinCode());
+    }
+
+    @Test
+    public void whenDoNarrowing_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        short pinCode = 4110;
+        pinCodeField.setInt(person, pinCode);
+        Assertions.assertEquals(pinCode, person.getPinCode());
+    }
+
+    @Test
+    public void whenSetFloatingTypeFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field heightField = person.getClass()
+            .getDeclaredField("height");
+        heightField.setAccessible(true);
+
+        float height = 6.1242f;
+        heightField.setFloat(person, height);
+        Assertions.assertEquals(height, person.getHeight());
+
+        Field weightField = person.getClass()
+            .getDeclaredField("weight");
+        weightField.setAccessible(true);
+
+        double weight = 75.2564;
+        weightField.setDouble(person, weight);
+        Assertions.assertEquals(weight, person.getWeight());
+    }
+
+    @Test
+    public void whenSetCharacterFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field genderField = person.getClass()
+            .getDeclaredField("gender");
+        genderField.setAccessible(true);
+
+        char gender = 'M';
+        genderField.setChar(person, gender);
+        Assertions.assertEquals(gender, person.getGender());
+    }
+
+    @Test
+    public void whenSetBooleanFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field activeField = person.getClass()
+            .getDeclaredField("active");
+        activeField.setAccessible(true);
+
+        activeField.setBoolean(person, true);
+        Assertions.assertTrue(person.isActive());
+    }
+
+    @Test
+    public void whenSetObjectFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+        nameField.setAccessible(true);
+
+        String name = "Umang Budhwar";
+        nameField.set(person, name);
+        Assertions.assertEquals(name, person.getName());
+    }
+
+    @Test
+    public void givenInt_whenSetStringField_thenIllegalArgumentException() throws Exception {
+        Person person = new Person();
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+        nameField.setAccessible(true);
+
+        Assertions.assertThrows(IllegalArgumentException.class, () -> nameField.setInt(person, 26));
+    }
+
+    @Test
+    public void givenInt_whenSetLongField_thenIllegalArgumentException() throws Exception {
+        Person person = new Person();
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        long pinCode = 411057L;
+
+        Assertions.assertThrows(IllegalArgumentException.class, () -> pinCodeField.setLong(person, pinCode));
+    }
+
+    @Test
+    public void whenFieldNotSetAccessible_thenIllegalAccessException() throws Exception {
+        Person person = new Person();
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+
+        Assertions.assertThrows(IllegalAccessException.class, () -> nameField.set(person, "Umang Budhwar"));
+    }
+
+    @Test
+    public void whenAccessingWrongProperty_thenNoSuchFieldException() throws Exception {
+        Person person = new Person();
+
+        Assertions.assertThrows(NoSuchFieldException.class, () -> person.getClass()
+            .getDeclaredField("firstName"));
+    }
+
+    @Test
+    public void whenAccessingNullProperty_thenNullPointerException() throws Exception {
+        Person person = new Person();
+
+        Assertions.assertThrows(NullPointerException.class, () -> person.getClass()
+            .getDeclaredField(null));
+    }
+
+}

core-java-modules/core-java-reflection/README.MD

@@ -8,5 +8,4 @@
 - [Changing Annotation Parameters At Runtime](http://www.baeldung.com/java-reflection-change-annotation-params)
 - [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
 - [What Causes java.lang.reflect.InvocationTargetException?](https://www.baeldung.com/java-lang-reflect-invocationtargetexception)
-- [How to Find all Getters Returning Null](http://www.baeldung.com/java-getters-returning-null)
 - [How to Get a Name of a Method Being Executed?](http://www.baeldung.com/java-name-of-executing-method)

core-java-modules/core-java-regex/README.md

@@ -3,6 +3,7 @@
 ## Core Java 8 Cookbooks and Examples
 
 ### Relevant Articles: 
+
 - [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
 - [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
 - [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
@@ -11,3 +12,4 @@
 - [How to Use Regular Expressions to Replace Tokens in Strings](https://www.baeldung.com/java-regex-token-replacement)
 - [Regular Expressions \s and \s+ in Java](https://www.baeldung.com/java-regex-s-splus)
 - [Validate Phone Numbers With Java Regex](https://www.baeldung.com/java-regex-validate-phone-numbers)
+- [How to Count the Number of Matches for a Regex?](https://www.baeldung.com/java-count-regex-matches)

core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/countmatches/CountMatchesUnitTest.java

@@ -1,12 +1,11 @@
 package com.baeldung.regex.countmatches;
 
-import static org.junit.Assert.assertNotEquals;
+import org.junit.Test;
-import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import org.junit.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 /**
  * Unit Test intended to count number of matches of a RegEx using Java 8 and 9.
@@ -65,7 +64,7 @@ public class CountMatchesUnitTest {
             count++;
         }
 
-        assertNotEquals(3, count);
+        assertEquals(2, count);
     }
 
     @Test

core-java-modules/core-java-security-2/README.md

@@ -9,4 +9,5 @@ This module contains articles about core Java Security
 - [Hashing a Password in Java](https://www.baeldung.com/java-password-hashing)
 - [SHA-256 and SHA3-256 Hashing in Java](https://www.baeldung.com/sha-256-hashing-java)
 - [Checksums in Java](https://www.baeldung.com/java-checksums)
+- [How to Read PEM File to Get Public and Private Keys](https://www.baeldung.com/java-read-pem-file-keys)
 - More articles: [[<-- prev]](/core-java-modules/core-java-security)

core-java-modules/core-java-string-operations-3/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Version Comparison in Java](https://www.baeldung.com/java-comparing-versions)