String to char array and char array to String (#1002)

* String to char array and char array to String.

* Method change

* Custom ThreadPool In Java 8 Parallel Streams

* Implemented suggested edits from editor.

* Broke long method signature

* Changed primitive type int to long and formula.

* Update wrapper type to Long

core-java/src/test/java/com/baeldung/CharArrayToStringUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class CharArrayToStringUnitTest {
+
+    @Test
+    public void givenCharArray_whenCallingStringConstructor_shouldConvertToString() {
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = new String(charArray);
+        String expectedValue = "character";
+        
+        assertEquals(expectedValue, result);
+    }
+    
+    @Test
+    public void givenCharArray_whenCallingStringConstructorWithOffsetAndLength_shouldConvertToString(){
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = new String(charArray, 4, 3);
+        String expectedValue = "act";
+        
+        assertEquals(expectedValue, result);
+    }
+    
+    @Test
+    public void givenCharArray_whenCallingStringCopyValueOf_shouldConvertToString(){
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = String.copyValueOf(charArray);
+        String expectedValue = "character";
+        
+        assertEquals(expectedValue, result);
+    }
+    
+    @Test
+    public void givenCharArray_whenCallingStringCopyValueOfWithOffsetAndLength_shouldConvertToString(){
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = String.copyValueOf(charArray, 0, 4);
+        String expectedValue = "char";
+        
+        assertEquals(expectedValue, result);
+    }
+    
+    @Test
+    public void givenCharArray_whenCallingStringValueOf_shouldConvertToString(){
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = String.valueOf(charArray);
+        String expectedValue = "character";
+        
+        assertEquals(expectedValue, result);
+    }
+    
+    @Test
+    public void givenCharArray_whenCallingStringValueOfWithOffsetAndLength_shouldConvertToString(){
+        char[] charArray = {'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r'};
+        String result = String.valueOf(charArray, 3, 4);
+        String expectedValue = "ract";
+        
+        assertEquals(expectedValue, result);
+    }
+}

core-java/src/test/java/com/baeldung/StringToCharArrayUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class StringToCharArrayUnitTest {
+
+@Test
+public void givenString_whenCallingStringToCharArray_shouldConvertToCharArray() {
+    String givenString = "characters";
+
+    char[] result = givenString.toCharArray();
+
+    char[] expectedCharArray = { 'c', 'h', 'a', 'r', 'a', 'c', 't', 'e', 'r', 's' };
+
+    assertArrayEquals(expectedCharArray, result);
+}
+
+}

core-java/src/test/java/org/baeldung/java/streams/ThreadPoolInParallelStream.java

@@ -0,0 +1,45 @@
+package org.baeldung.java.streams;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ForkJoinPool;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+public class ThreadPoolInParallelStream {
+    
+    @Test
+    public void giveRangeOfLongs_whenSummedInParallel_shouldBeEqualToExpectedTotal() 
+        throws InterruptedException, ExecutionException {
+        List<Long> aList = new ArrayList<>();        
+        long lastNum = 1_000_000;    
+        long firstNum = 1;
+        
+        long expectedTotal = (lastNum + firstNum) * lastNum / 2;
+        
+        for(long i = firstNum; i <= lastNum; i++){
+            aList.add(i);
+        } 
+        
+        ForkJoinPool customThreadPool = new ForkJoinPool(4);
+        long actualTotal = customThreadPool.submit(() -> aList.parallelStream().reduce(
+            0L, (x, y) -> { 
+                return x + y;
+            })).get();
+        
+        assertEquals(expectedTotal, actualTotal);
+    }
+    
+    @Test
+    public void givenList_whenCallingParallelStream_shouldBeParallelStream(){
+        List<Long> aList = new ArrayList<>();
+        Stream<Long> parallelStream = aList.parallelStream();
+        
+        assertTrue(parallelStream.isParallel());
+    }
+}