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BAEL-3209 - Adding elements in Java Array vs ArrayList
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‎core-java-modules/core-java-arrays-2/src/main/java/com/baeldung/array/operations/ArrayOperations.java‎

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

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

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

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

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

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

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

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