Merge pull request #16675 from sk1418/insert-1st-array

[insert-1st-array] prepend an element to an array

Author: theangrydev

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

@@ -1,14 +1,19 @@
 package com.baeldung.array.operations;
 
-import org.apache.commons.lang3.ArrayUtils;
-
 import java.lang.reflect.Array;
-import java.util.*;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.LinkedList;
+import java.util.Random;
+import java.util.Set;
 import java.util.function.Function;
 import java.util.function.IntPredicate;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
+import org.apache.commons.lang3.ArrayUtils;
+
 public class ArrayOperations {
 
     // Get the first and last item of an array
@@ -225,7 +230,7 @@ public static Integer[] addElementUsingPureJava(Integer[] srcArray, int elementT
     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++) {
+        for (int i = 0; i < destArray.length; i++) {
 
             if (i == index) {
                 destArray[i] = newElement;
@@ -236,4 +241,11 @@ public static int[] insertAnElementAtAGivenIndex(final int[] srcArray, int index
         }
         return destArray;
     }
-}
+
+    public static int[] prependAnElementToArray(int[] srcArray, int element) {
+        int[] newArray =  new int[srcArray.length + 1];
+        newArray[0] = element;
+        System.arraycopy(srcArray, 0, newArray, 1, srcArray.length);
+        return newArray;
+    }
+}

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

@@ -1,11 +1,14 @@
 package com.baeldung.array.operations;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertArrayEquals;
+
 import java.util.Arrays;
+
+import org.apache.commons.lang3.ArrayUtils;
 import org.assertj.core.api.Condition;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.junit.Assert.assertArrayEquals;
 
 public class ArrayOperationsUnitTest {
 
@@ -314,7 +317,8 @@ public void whenShufflingIntArraySeveralTimes_thenAtLeastOneWithDifferentOrder()
         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);
+                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);
             }
         };
 
@@ -333,7 +337,8 @@ public void whenShufflingObjectArraySeveralTimes_thenAtLeastOneWithDifferentOrde
         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);
+                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);
             }
         };
 
@@ -367,14 +372,38 @@ public void givenSourceArrayAndElement_whenAddElementUsingPureJavaIsInvoked_then
     }
 
     @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);
+    void whenInsertAnElementAtAGivenIndexCalled_thenShiftTheFollowingElementsAndInsertTheElementInArray() {
+        int[] expectedArray = { 1, 2, 42, 3, 4 };
+        int[] anArray = { 1, 2, 3, 4 };
+        int[] outputArray = ArrayOperations.insertAnElementAtAGivenIndex(anArray, 2, 42);
 
         assertThat(outputArray).containsExactly(expectedArray);
     }
-}
+
+    @Test
+    void whenPrependingAnElementUsingInsertAnElementAtAGivenIndex_thenGetExpectedResult() {
+        int[] anArray = { 1, 2, 3, 4 };
+        int[] expectedArray = { 42, 1, 2, 3, 4 };
+        int[] result = ArrayOperations.insertAnElementAtAGivenIndex(anArray, 0, 42);
+
+        assertThat(result).containsExactly(expectedArray);
+    }
+
+    @Test
+    void whenUsingPrependAnElementToArray_thenGetExpectedResult() {
+        int[] anArray = { 1, 2, 3, 4 };
+        int[] expectedArray = { 42, 1, 2, 3, 4 };
+        int[] result = ArrayOperations.prependAnElementToArray(anArray, 42);
+
+        assertThat(result).containsExactly(expectedArray);
+    }
+
+    @Test
+    void whenPrependingAnElementUsingArrayUtils_thenGetExpectedResult() {
+        int[] anArray = { 1, 2, 3, 4 };
+        int[] expectedArray = { 42, 1, 2, 3, 4 };
+        int[] result = ArrayUtils.addFirst(anArray, 42);
+
+        assertThat(result).containsExactly(expectedArray);
+    }
+}