BAEL-3209 - Adding elements in Java Array vs ArrayList

core-java-modules/core-java-arrays-2/src/main/java/com/baeldung/array/operations/ArrayOperations.java

@@ -0,0 +1,30 @@
+package com.baeldung.array.operations;
+
+public class ArrayOperations {
+
+    public static Integer[] addElementUsingPureJava(Integer[] srcArray, int elementToAdd) {
+        Integer[] destArray = new Integer[srcArray.length + 1];
+
+        for (int i = 0; i < srcArray.length; i++) {
+            destArray[i] = srcArray[i];
+        }
+
+        destArray[destArray.length - 1] = elementToAdd;
+        return destArray;
+    }
+
+    public static int[] insertAnElementAtAGivenIndex(final int[] srcArray, int index, int newElement) {
+        int[] destArray = new int[srcArray.length + 1];
+        int j = 0;
+        for (int i = 0; i < destArray.length - 1; i++) {
+
+            if (i == index) {
+                destArray[i] = newElement;
+            } else {
+                destArray[i] = srcArray[j];
+                j++;
+            }
+        }
+        return destArray;
+    }
+}

core-java-modules/core-java-arrays-2/src/main/java/com/baeldung/arraylist/operations/ArrayListOperations.java

@@ -0,0 +1,23 @@
+package com.baeldung.arraylist.operations;
+
+import java.util.ArrayList;
+
+public class ArrayListOperations {
+
+    public static Integer getAnIntegerElement(ArrayList<Integer> anArrayList, int index) {
+        return anArrayList.get(index);
+    }
+
+    public static void modifyAnIntegerElement(ArrayList<Integer> anArrayList, int index, Integer newElement) {
+        anArrayList.set(index, newElement);
+    }
+
+    public static void appendAnIntegerElement(ArrayList<Integer> anArrayList, Integer newElement) {
+        anArrayList.add(newElement);
+    }
+
+    public static void insertAnIntegerElementAtIndex(ArrayList<Integer> anArrayList, int index, Integer newElement) {
+        anArrayList.add(index, newElement);
+    }
+
+}

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/array/operations/ArrayOperationsUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.array.operations;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.Assert.assertArrayEquals;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ArrayOperationsUnitTest {
+
+    @Test
+    public void givenSourceArrayAndElement_whenAddElementUsingPureJavaIsInvoked_thenNewElementMustBeAdded() {
+        Integer[] sourceArray = { 1, 2, 3, 4 };
+        int elementToAdd = 5;
+
+        Integer[] destArray = ArrayOperations.addElementUsingPureJava(sourceArray, elementToAdd);
+
+        Integer[] expectedArray = { 1, 2, 3, 4, 5 };
+        assertArrayEquals(expectedArray, destArray);
+    }
+
+    @Test
+    public void whenInsertAnElementAtAGivenIndexCalled_thenShiftTheFollowingElementsAndInsertTheElementInArray() {
+        int[] expectedArray = { 1, 4, 2, 3, 0 };
+        int[] anArray = new int[4];
+        anArray[0] = 1;
+        anArray[1] = 2;
+        anArray[2] = 3;
+        int[] outputArray = ArrayOperations.insertAnElementAtAGivenIndex(anArray, 1, 4);
+
+        assertThat(outputArray).containsExactly(expectedArray);
+    }
+
+}

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/arraylist/operations/ArrayListOperationsUnitTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.arraylist.operations;
+
+import java.util.ArrayList;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ArrayListOperationsUnitTest {
+
+    private ArrayList<Integer> anArrayList;
+
+    @BeforeEach
+    public void setupDefaults() {
+        anArrayList = new ArrayList<>();
+        anArrayList.add(2);
+        anArrayList.add(3);
+        anArrayList.add(4);
+    }
+
+    @Test
+    public void whenGetAnIntegerElementCalled_thenReturnTheIntegerElement() {
+        Integer output = ArrayListOperations.getAnIntegerElement(anArrayList, 1);
+
+        assertThat(output).isEqualTo(3);
+    }
+
+    @Test
+    public void whenModifyAnIntegerElementCalled_thenModifyTheIntegerElement() {
+        ArrayListOperations.modifyAnIntegerElement(anArrayList, 2, 5);
+        Integer output = ArrayListOperations.getAnIntegerElement(anArrayList, 2);
+
+        assertThat(output).isEqualTo(5);
+    }
+
+    @Test
+    public void whenAppendAnIntegerElementCalled_thenTheIntegerElementIsAppendedToArrayList() {
+        ArrayListOperations.appendAnIntegerElement(anArrayList, 6);
+        Integer output = ArrayListOperations.getAnIntegerElement(anArrayList, anArrayList.size() - 1);
+
+        assertThat(output).isEqualTo(6);
+    }
+
+    @Test
+    public void whenInsertAnIntegerAtIndexCalled_thenTheIntegerElementIsInseredToArrayList() {
+        ArrayListOperations.insertAnIntegerElementAtIndex(anArrayList, 1, 10);
+        Integer output = ArrayListOperations.getAnIntegerElement(anArrayList, 1);
+
+        assertThat(output).isEqualTo(10);
+    }
+}