[BAEL-2235] | core-java | Common Array Operations in Java (#5599)

* * added all array operations and tests

* fixed details, adn added some more methods to java array operations examples

* * moved arrays operations package to core-java-collections submodule

core-java-collections/pom.xml

@@ -61,7 +61,7 @@
     <properties>
         <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <junit.platform.version>1.2.0</junit.platform.version>
-        <commons-lang3.version>3.5</commons-lang3.version>
+        <commons-lang3.version>3.8.1</commons-lang3.version>
         <commons-collections4.version>4.1</commons-collections4.version>
         <collections-generic.version>4.01</collections-generic.version>
         <avaitility.version>1.7.0</avaitility.version>

core-java-collections/src/main/java/com/baeldung/array/operations/ArrayOperations.java

@@ -0,0 +1,197 @@
+package com.baeldung.array.operations;
+
+import java.lang.reflect.Array;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.Random;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.function.IntPredicate;
+import java.util.function.Predicate;
+
+import org.apache.commons.lang3.ArrayUtils;
+
+public class ArrayOperations {
+
+    // Get the first and last item of an array
+    public static <T> T getFirstObject(T[] array) {
+        return array[0];
+    }
+
+    public static int getFirstInt(int[] array) {
+        return array[0];
+    }
+
+    public static <T> T getLastObject(T[] array) {
+        return array[array.length - 1];
+    }
+
+    public static int getLastInt(int[] array) {
+        return array[array.length - 1];
+    }
+
+    // Append a new item to an array
+    public static <T> T[] appendObject(T[] array, T newItem) {
+        return ArrayUtils.add(array, newItem);
+    }
+
+    public static int[] appendInt(int[] array, int newItem) {
+        int[] newArray = Arrays.copyOf(array, array.length + 1);
+        newArray[newArray.length - 1] = newItem;
+        return newArray;
+    }
+
+    public static int[] appendIntWithUtils(int[] array, int newItem) {
+        return ArrayUtils.add(array, newItem);
+    }
+
+    // Compare two arrays to check if they have the same elements
+    public static <T> boolean compareObjectArrays(T[] array1, T[] array2) {
+        return Arrays.equals(array1, array2);
+    }
+
+    public static boolean compareIntArrays(int[] array1, int[] array2) {
+        return Arrays.equals(array1, array2);
+    }
+
+    // Deep Compare (for nested arrays)
+    public static <T> boolean deepCompareObjectArrayUsingArrays(T[][] array1, T[][] array2) {
+        // We can use Objects.deepEquals for a broader approach
+        return Arrays.deepEquals(array1, array2);
+    }
+
+    public static boolean deepCompareIntArrayUsingArrays(int[][] array1, int[][] array2) {
+        return Arrays.deepEquals(array1, array2);
+    }
+
+    // Check if array is empty
+    public static <T> boolean isEmptyObjectArrayUsingUtils(T[] array1) {
+        return ArrayUtils.isEmpty(array1);
+    }
+
+    public static boolean isEmptyIntArrayUsingUtils(int[] array1) {
+        return ArrayUtils.isEmpty(array1);
+    }
+
+    // Remove duplicates
+    public static Integer[] removeDuplicateObjects(Integer[] array) {
+        // We can use other ways of converting the array to a set too
+        Set<Integer> set = new HashSet<>(Arrays.asList(array));
+        return set.toArray(new Integer[set.size()]);
+    }
+
+    public static int[] removeDuplicateInts(int[] array) {
+        // Box
+        Integer[] list = ArrayUtils.toObject(array);
+        // Remove duplicates
+        Set<Integer> set = new HashSet<Integer>(Arrays.asList(list));
+        // Create array and unbox
+        return ArrayUtils.toPrimitive(set.toArray(new Integer[set.size()]));
+    }
+
+    // Remove duplicates preserving the order
+    public static Integer[] removeDuplicateWithOrderObjectArray(Integer[] array) {
+        // We can use other ways of converting the array to a set too
+        Set<Integer> set = new LinkedHashSet<>(Arrays.asList(array));
+        return set.toArray(new Integer[set.size()]);
+    }
+
+    public static int[] removeDuplicateWithOrderIntArray(int[] array) {
+        // Box
+        Integer[] list = ArrayUtils.toObject(array);
+        // Remove duplicates
+        Set<Integer> set = new LinkedHashSet<Integer>(Arrays.asList(list));
+        // Create array and unbox
+        return ArrayUtils.toPrimitive(set.toArray(new Integer[set.size()]));
+    }
+
+    // Print an array
+    public static String printObjectArray(Integer[] array) {
+        return ArrayUtils.toString(array);
+    }
+
+    public static String printObjectArray(Integer[][] array) {
+        return ArrayUtils.toString(array);
+    }
+
+    public static String printIntArray(int[] array) {
+        return ArrayUtils.toString(array);
+    }
+
+    public static String printIntArray(int[][] array) {
+        return ArrayUtils.toString(array);
+    }
+
+    // Box or Unbox values
+    public static int[] unboxIntegerArray(Integer[] array) {
+        return ArrayUtils.toPrimitive(array);
+    }
+
+    public static Integer[] boxIntArray(int[] array) {
+        return ArrayUtils.toObject(array);
+    }
+
+    // Map array values
+    @SuppressWarnings("unchecked")
+    public static <T, U> U[] mapObjectArray(T[] array, Function<T, U> function, Class<U> targetClazz) {
+        U[] newArray = (U[]) Array.newInstance(targetClazz, array.length);
+        for (int i = 0; i < array.length; i++) {
+            newArray[i] = function.apply(array[i]);
+        }
+        return newArray;
+    }
+
+    public static String[] mapIntArrayToString(int[] array) {
+        return Arrays.stream(array)
+            .mapToObj(value -> String.format("Value: %s", value))
+            .toArray(String[]::new);
+    }
+
+    // Filter array values
+    public static Integer[] filterObjectArray(Integer[] array, Predicate<Integer> predicate) {
+        return Arrays.stream(array)
+            .filter(predicate)
+            .toArray(Integer[]::new);
+    }
+
+    public static int[] filterIntArray(int[] array, IntPredicate predicate) {
+        return Arrays.stream(array)
+            .filter(predicate)
+            .toArray();
+    }
+
+    // Insert item between others
+    public static int[] insertBetweenIntArray(int[] array, int... values) {
+        return ArrayUtils.insert(2, array, values);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <T> T[] insertBetweenObjectArray(T[] array, T... values) {
+        return ArrayUtils.insert(2, array, values);
+    }
+
+    // Shuffling arrays
+    public static int[] shuffleIntArray(int[] array) {
+        // we create a different array instance for testing purposes
+        int[] shuffled = Arrays.copyOf(array, array.length);
+        ArrayUtils.shuffle(shuffled);
+        return shuffled;
+    }
+
+    public static <T> T[] shuffleObjectArray(T[] array) {
+        // we create a different array instance for testing purposes
+        T[] shuffled = Arrays.copyOf(array, array.length);
+        ArrayUtils.shuffle(shuffled);
+        return shuffled;
+    }
+
+    // Get random number
+    public static int getRandomFromIntArray(int[] array) {
+        return array[new Random().nextInt(array.length)];
+    }
+
+    public static <T> T getRandomFromObjectArray(T[] array) {
+        return array[new Random().nextInt(array.length)];
+    }
+}

core-java-collections/src/test/java/com/baeldung/array/operations/ArrayOperationsUnitTest.java

@@ -0,0 +1,365 @@
+package com.baeldung.array.operations;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+
+import org.assertj.core.api.Condition;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class ArrayOperationsUnitTest {
+
+    private Integer[] defaultObjectArray;
+    private int[] defaultIntArray;
+    private Integer[][] defaultJaggedObjectArray;
+    private int[][] defaultJaggedIntArray;
+
+    @BeforeEach
+    public void setupDefaults() {
+        defaultObjectArray = new Integer[] { 3, 5, 2, 5, 14, 4 };
+        defaultIntArray = new int[] { 3, 5, 2, 5, 14, 4 };
+        defaultJaggedObjectArray = new Integer[][] { { 1, 3 }, { 5 }, {} };
+        defaultJaggedIntArray = new int[][] { { 1, 3 }, { 5 }, {} };
+    }
+
+    // Get the first and last item of an array
+    @Test
+    public void whenGetFirstObjectCalled_thenReturnFirstItemOfArray() {
+        Integer output = ArrayOperations.getFirstObject(defaultObjectArray);
+
+        assertThat(output).isEqualTo(3);
+    }
+
+    @Test
+    public void whenGetFirstIntCalled_thenReturnFirstItemOfArray() {
+        int output = ArrayOperations.getFirstInt(defaultIntArray);
+
+        assertThat(output).isEqualTo(3);
+    }
+
+    @Test
+    public void whenGetLastObjectCalled_thenReturnLastItemOfArray() {
+        Integer output = ArrayOperations.getLastObject(defaultObjectArray);
+
+        assertThat(output).isEqualTo(4);
+    }
+
+    @Test
+    public void whenGetLastIntCalled_thenReturnLastItemOfArray() {
+        int output = ArrayOperations.getLastInt(defaultIntArray);
+
+        assertThat(output).isEqualTo(4);
+    }
+
+    // Append a new item to an array
+    @Test
+    public void whenAppendObject_thenReturnArrayWithExtraItem() {
+        Integer[] output = ArrayOperations.appendObject(defaultObjectArray, 7);
+
+        assertThat(output).endsWith(4, 7)
+            .hasSize(7);
+    }
+
+    @Test
+    public void whenAppendInt_thenReturnArrayWithExtraItem() {
+        int[] output = ArrayOperations.appendInt(defaultIntArray, 7);
+        int[] outputUsingUtils = ArrayOperations.appendIntWithUtils(defaultIntArray, 7);
+
+        assertThat(output).endsWith(4, 7)
+            .hasSize(7);
+        assertThat(outputUsingUtils).endsWith(4, 7)
+            .hasSize(7);
+    }
+
+    // Compare two arrays to check if they have the same elements
+    @Test
+    public void whenCompareObjectArrays_thenReturnBoolean() {
+        Integer[] array2 = { 8, 7, 6 };
+        Integer[] sameArray = { 3, 5, 2, 5, 14, 4 };
+        boolean output = ArrayOperations.compareObjectArrays(defaultObjectArray, array2);
+        boolean output2 = ArrayOperations.compareObjectArrays(defaultObjectArray, sameArray);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+    }
+
+    @Test
+    public void whenCompareIntArrays_thenReturnBoolean() {
+        int[] array2 = { 8, 7, 6 };
+        int[] sameArray = { 3, 5, 2, 5, 14, 4 };
+        boolean output = ArrayOperations.compareIntArrays(defaultIntArray, array2);
+        boolean output2 = ArrayOperations.compareIntArrays(defaultIntArray, sameArray);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+    }
+
+    // Deep compare
+    @Test
+    public void whenDeepCompareObjectArrays_thenReturnBoolean() {
+        Integer[][] sameArray = { { 1, 3 }, { 5 }, {} };
+        Integer[][] array2 = { { 1, 3 }, { 5 }, { 3 } };
+        boolean output = ArrayOperations.deepCompareObjectArrayUsingArrays(defaultJaggedObjectArray, array2);
+        boolean output2 = ArrayOperations.deepCompareObjectArrayUsingArrays(defaultJaggedObjectArray, sameArray);
+        // Because arrays are Objects, we could wrongly use the non-deep approach
+        boolean outputUsingNonDeep = ArrayOperations.compareObjectArrays(defaultJaggedObjectArray, sameArray);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+        // This is not what we would expect!
+        assertThat(outputUsingNonDeep).isFalse();
+    }
+
+    @Test
+    public void whenDeepCompareIntArrays_thenReturnBoolean() {
+        int[][] sameArray = { { 1, 3 }, { 5 }, {} };
+        int[][] array2 = { { 1, 3 }, { 5 }, { 3 } };
+        boolean output = ArrayOperations.deepCompareIntArrayUsingArrays(defaultJaggedIntArray, array2);
+        boolean output2 = ArrayOperations.deepCompareIntArrayUsingArrays(defaultJaggedIntArray, sameArray);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+    }
+
+    // Empty Check
+    @Test
+    public void whenIsEmptyObjectArray_thenReturnBoolean() {
+        Integer[] array2 = {};
+        Integer[] array3 = null;
+        Integer[] array4 = { null, null, null };
+        Integer[] array5 = { null };
+        Integer[][] array6 = { {}, {}, {} };
+        boolean output = ArrayOperations.isEmptyObjectArrayUsingUtils(defaultObjectArray);
+        boolean output2 = ArrayOperations.isEmptyObjectArrayUsingUtils(array2);
+        boolean output3 = ArrayOperations.isEmptyObjectArrayUsingUtils(array3);
+        boolean output4 = ArrayOperations.isEmptyObjectArrayUsingUtils(array4);
+        boolean output5 = ArrayOperations.isEmptyObjectArrayUsingUtils(array5);
+        boolean output6 = ArrayOperations.isEmptyObjectArrayUsingUtils(array6);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+        assertThat(output3).isTrue();
+        // Mind these edge cases!
+        assertThat(output4).isFalse();
+        assertThat(output5).isFalse();
+        assertThat(output6).isFalse();
+    }
+
+    @Test
+    public void whenIsEmptyIntArray_thenReturnBoolean() {
+        int[] array2 = {};
+        boolean output = ArrayOperations.isEmptyIntArrayUsingUtils(defaultIntArray);
+        boolean output2 = ArrayOperations.isEmptyIntArrayUsingUtils(array2);
+
+        assertThat(output).isFalse();
+        assertThat(output2).isTrue();
+    }
+
+    // Remove Duplicates
+    @Test
+    public void whenRemoveDuplicateObjectArray_thenReturnArrayWithNoDuplicates() {
+        Integer[] output = ArrayOperations.removeDuplicateObjects(defaultObjectArray);
+
+        assertThat(output).containsOnlyOnce(5)
+            .hasSize(5)
+            .doesNotHaveDuplicates();
+    }
+
+    @Test
+    public void whenRemoveDuplicateIntArray_thenReturnArrayWithNoDuplicates() {
+        int[] output = ArrayOperations.removeDuplicateInts(defaultIntArray);
+
+        assertThat(output).containsOnlyOnce(5)
+            .hasSize(5)
+            .doesNotHaveDuplicates();
+    }
+
+    // Remove Duplicates Preserving order
+    @Test
+    public void whenRemoveDuplicatePreservingOrderObjectArray_thenReturnArrayWithNoDuplicates() {
+        Integer[] array2 = { 3, 5, 2, 14, 4 };
+        Integer[] output = ArrayOperations.removeDuplicateWithOrderObjectArray(defaultObjectArray);
+
+        assertThat(output).containsOnlyOnce(5)
+            .hasSize(5)
+            .containsExactly(array2);
+    }
+
+    @Test
+    public void whenRemoveDuplicatePreservingOrderIntArray_thenReturnArrayWithNoDuplicates() {
+        int[] array2 = { 3, 5, 2, 14, 4 };
+        int[] output = ArrayOperations.removeDuplicateWithOrderIntArray(defaultIntArray);
+
+        assertThat(output).containsOnlyOnce(5)
+            .hasSize(5)
+            .containsExactly(array2);
+    }
+
+    // Print
+    @Test
+    public void whenPrintObjectArray_thenReturnString() {
+        String output = ArrayOperations.printObjectArray(defaultObjectArray);
+        String jaggedOutput = ArrayOperations.printObjectArray(defaultJaggedObjectArray);
+        // Comparing to Arrays output:
+        String wrongArraysOutput = Arrays.toString(defaultJaggedObjectArray);
+        String differentFormatArraysOutput = Arrays.toString(defaultObjectArray);
+        // We should use Arrays.deepToString for jagged arrays
+        String differentFormatJaggedArraysOutput = Arrays.deepToString(defaultJaggedObjectArray);
+
+        assertThat(output).isEqualTo("{3,5,2,5,14,4}");
+        assertThat(jaggedOutput).isEqualTo("{{1,3},{5},{}}");
+        assertThat(differentFormatArraysOutput).isEqualTo("[3, 5, 2, 5, 14, 4]");
+        assertThat(wrongArraysOutput).contains("[[Ljava.lang.Integer;@");
+        assertThat(differentFormatJaggedArraysOutput).contains("[[1, 3], [5], []]");
+    }
+
+    @Test
+    public void whenPrintIntArray_thenReturnString() {
+        String output = ArrayOperations.printIntArray(defaultIntArray);
+        String jaggedOutput = ArrayOperations.printIntArray(defaultJaggedIntArray);
+        // Comparing to Arrays output:
+        String wrongArraysOutput = Arrays.toString(defaultJaggedObjectArray);
+        String differentFormatArraysOutput = Arrays.toString(defaultObjectArray);
+
+        assertThat(output).isEqualTo("{3,5,2,5,14,4}");
+        assertThat(jaggedOutput).isEqualTo("{{1,3},{5},{}}");
+        assertThat(differentFormatArraysOutput).isEqualTo("[3, 5, 2, 5, 14, 4]");
+        assertThat(wrongArraysOutput).contains("[[Ljava.lang.Integer;@");
+    }
+
+    // Box and unbox
+    @Test
+    public void whenUnboxObjectArray_thenReturnPrimitiveArray() {
+        int[] output = ArrayOperations.unboxIntegerArray(defaultObjectArray);
+
+        assertThat(output).containsExactly(defaultIntArray);
+    }
+
+    @Test
+    public void henBoxPrimitiveArray_thenReturnObjectArray() {
+        Integer[] output = ArrayOperations.boxIntArray(defaultIntArray);
+
+        assertThat(output).containsExactly(defaultObjectArray);
+    }
+
+    // Map values
+    @Test
+    public void whenMapMultiplyingObjectArray_thenReturnMultipliedArray() {
+        Integer[] multipliedExpectedArray = new Integer[] { 6, 10, 4, 10, 28, 8 };
+        Integer[] output = ArrayOperations.mapObjectArray(defaultObjectArray, value -> value * 2, Integer.class);
+
+        assertThat(output).containsExactly(multipliedExpectedArray);
+    }
+
+    @Test
+    public void whenMapDividingObjectArray_thenReturnDividedArray() {
+        Double[] multipliedExpectedArray = new Double[] { 1.5, 2.5, 1.0, 2.5, 7.0, 2.0 };
+        Double[] output = ArrayOperations.mapObjectArray(defaultObjectArray, value -> value / 2.0, Double.class);
+
+        assertThat(output).containsExactly(multipliedExpectedArray);
+    }
+
+    @Test
+    public void whenMapIntArrayToString_thenReturnArray() {
+        String[] expectedArray = new String[] { "Value: 3", "Value: 5", "Value: 2", "Value: 5", "Value: 14",
+                "Value: 4" };
+        String[] output = ArrayOperations.mapIntArrayToString(defaultIntArray);
+
+        assertThat(output).containsExactly(expectedArray);
+    }
+
+    // Filter values
+    @Test
+    public void whenFilterObjectArray_thenReturnFilteredArray() {
+        Integer[] multipliedExpectedArray = new Integer[] { 2, 14, 4 };
+        Integer[] output = ArrayOperations.filterObjectArray(defaultObjectArray, value -> value % 2 == 0);
+
+        assertThat(output).containsExactly(multipliedExpectedArray);
+    }
+
+    @Test
+    public void whenFilterIntArray_thenReturnFilteredArray() {
+        int[] expectedArray = new int[] { 2, 14, 4 };
+        int[] output = ArrayOperations.filterIntArray(defaultIntArray, value -> (int) value % 2 == 0);
+
+        assertThat(output).containsExactly(expectedArray);
+    }
+
+    // Insert between
+    @Test
+    public void whenInsertBetweenIntArrayToString_thenReturnNewArray() {
+        int[] expectedArray = { 3, 5, 77, 88, 2, 5, 14, 4 };
+        int[] output = ArrayOperations.insertBetweenIntArray(defaultIntArray, 77, 88);
+
+        assertThat(output).containsExactly(expectedArray);
+    }
+
+    @Test
+    public void whenInsertBetweenObjectArrayToString_thenReturnNewArray() {
+        Integer[] expectedArray = { 3, 5, 77, 99, 2, 5, 14, 4 };
+        Integer[] output = ArrayOperations.insertBetweenObjectArray(defaultObjectArray, 77, 99);
+
+        assertThat(output).containsExactly(expectedArray);
+    }
+
+    // Shuffle between
+    @Test
+    public void whenShufflingIntArraySeveralTimes_thenAtLeastOneWithDifferentOrder() {
+        int[] output = ArrayOperations.shuffleIntArray(defaultIntArray);
+        int[] output2 = ArrayOperations.shuffleIntArray(defaultIntArray);
+        int[] output3 = ArrayOperations.shuffleIntArray(defaultIntArray);
+        int[] output4 = ArrayOperations.shuffleIntArray(defaultIntArray);
+        int[] output5 = ArrayOperations.shuffleIntArray(defaultIntArray);
+        int[] output6 = ArrayOperations.shuffleIntArray(defaultIntArray);
+
+        Condition<int[]> atLeastOneArraysIsNotEqual = new Condition<int[]>(
+            "at least one output should be different (order-wise)") {
+            @Override
+            public boolean matches(int[] value) {
+                return !Arrays.equals(value, output) || !Arrays.equals(value, output2) || !Arrays.equals(value, output3)
+                    || !Arrays.equals(value, output4) || !Arrays.equals(value, output5)
+                    || !Arrays.equals(value, output6);
+            }
+        };
+
+        assertThat(defaultIntArray).has(atLeastOneArraysIsNotEqual);
+    }
+
+    @Test
+    public void whenShufflingObjectArraySeveralTimes_thenAtLeastOneWithDifferentOrder() {
+        Integer[] output = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+        Integer[] output2 = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+        Integer[] output3 = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+        Integer[] output4 = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+        Integer[] output5 = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+        Integer[] output6 = ArrayOperations.shuffleObjectArray(defaultObjectArray);
+
+        Condition<Integer[]> atLeastOneArraysIsNotEqual = new Condition<Integer[]>(
+            "at least one output should be different (order-wise)") {
+            @Override
+            public boolean matches(Integer[] value) {
+                return !Arrays.equals(value, output) || !Arrays.equals(value, output2) || !Arrays.equals(value, output3)
+                    || !Arrays.equals(value, output4) || !Arrays.equals(value, output5)
+                    || !Arrays.equals(value, output6);
+            }
+        };
+
+        assertThat(defaultObjectArray).has(atLeastOneArraysIsNotEqual);
+    }
+
+    // Get random item
+    @Test
+    public void whenGetRandomFromIntArrayToString_thenReturnItemContainedInArray() {
+        int output = ArrayOperations.getRandomFromIntArray(defaultIntArray);
+
+        assertThat(defaultIntArray).contains(output);
+    }
+
+    @Test
+    public void whenGetRandomFromObjectArrayToString_thenReturnItemContainedInArray() {
+        Integer output = ArrayOperations.getRandomFromObjectArray(defaultObjectArray);
+
+        assertThat(defaultObjectArray).contains(output);
+    }
+}