BAEL-1250 Initializing Arrays in Java

core-java/src/main/java/com/baeldung/array/ArrayInitializer.java

@@ -0,0 +1,74 @@
+package com.baeldung.array;
+
+import java.util.Arrays;
+
+public class ArrayInitializer {
+
+    public static int[] initializeArrayInLoop() {
+        int array[] = new int[5];
+        for (int i = 0; i < array.length; i++)
+            array[i] = i + 2;
+        return array;
+    }
+
+    public static int[][] initializeMultiDimensionalArrayInLoop() {
+        int array[][] = new int[2][5];
+        for (int i = 0; i < 2; i++)
+            for (int j = 0; j < 5; j++)
+                array[i][j] = j + 1;
+        return array;
+    }
+
+    public static String[] initializeArrayAtTimeOfDeclarationMethod1() {
+        String array[] = new String[] { "Toyota", "Mercedes", "BMW", "Volkswagen", "Skoda" };
+        return array;
+    }
+
+    public static int[] initializeArrayAtTimeOfDeclarationMethod2() {
+        int[] array = new int[] { 1, 2, 3, 4, 5 };
+        return array;
+    }
+
+    public static int[] initializeArrayAtTimeOfDeclarationMethod3() {
+        int array[] = { 1, 2, 3, 4, 5 };
+        return array;
+    }
+
+    public static long[] initializeArrayUsingArraysFill() {
+        long array[] = new long[5];
+        Arrays.fill(array, 30);
+        return array;
+    }
+
+    public static int[] initializeArrayRangeUsingArraysFill() {
+        int array[] = new int[5];
+        Arrays.fill(array, 0, 3, -50);
+        return array;
+    }
+
+    public static int[] initializeArrayUsingArraysCopy() {
+        int array[] = { 1, 2, 3, 4, 5 };
+        int[] copy = Arrays.copyOf(array, 5);
+        return copy;
+    }
+
+    public static int[] initializeLargerArrayUsingArraysCopy() {
+        int array[] = { 1, 2, 3, 4, 5 };
+        int[] copy = Arrays.copyOf(array, 6);
+        return copy;
+    }
+
+    public static int[] initializeArrayUsingArraysSetAll() {
+        int[] array = new int[20];
+
+        for (int i = 0; i < 20; i++) {
+            Arrays.setAll(array, p -> {
+                if (p > 9)
+                    return 0;
+                else
+                    return p;
+            });
+        }
+        return array;
+    }
+}

core-java/src/test/java/com/baeldung/array/ArrayInitializerTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.array;
+
+import static com.baeldung.array.ArrayInitializer.initializeArrayAtTimeOfDeclarationMethod1;
+import static com.baeldung.array.ArrayInitializer.initializeArrayAtTimeOfDeclarationMethod2;
+import static com.baeldung.array.ArrayInitializer.initializeArrayAtTimeOfDeclarationMethod3;
+import static com.baeldung.array.ArrayInitializer.initializeArrayInLoop;
+import static com.baeldung.array.ArrayInitializer.initializeArrayRangeUsingArraysFill;
+import static com.baeldung.array.ArrayInitializer.initializeArrayUsingArraysCopy;
+import static com.baeldung.array.ArrayInitializer.initializeArrayUsingArraysFill;
+import static com.baeldung.array.ArrayInitializer.initializeArrayUsingArraysSetAll;
+import static com.baeldung.array.ArrayInitializer.initializeLargerArrayUsingArraysCopy;
+import static com.baeldung.array.ArrayInitializer.initializeMultiDimensionalArrayInLoop;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class ArrayInitializerTest {
+
+    @Test
+    public void whenInitializeArrayInLoop_thenCorrect() {
+        assertArrayEquals(new int[] { 2, 3, 4, 5, 6 }, initializeArrayInLoop());
+    }
+
+    @Test
+    public void whenInitializeMultiDimensionalArrayInLoop_thenCorrect() {
+        assertArrayEquals(new int[][] { { 1, 2, 3, 4, 5 }, { 1, 2, 3, 4, 5 } }, initializeMultiDimensionalArrayInLoop());
+    }
+
+    @Test
+    public void whenInitializeArrayAtTimeOfDeclarationMethod1_thenCorrect() {
+        assertArrayEquals(new String[] { "Toyota", "Mercedes", "BMW", "Volkswagen", "Skoda" }, initializeArrayAtTimeOfDeclarationMethod1());
+    }
+
+    @Test
+    public void whenInitializeArrayAtTimeOfDeclarationMethod2_thenCorrect() {
+        assertArrayEquals(new int[] { 1, 2, 3, 4, 5 }, initializeArrayAtTimeOfDeclarationMethod2());
+    }
+
+    @Test
+    public void whenInitializeArrayAtTimeOfDeclarationMethod3_thenCorrect() {
+        assertArrayEquals(new int[] { 1, 2, 3, 4, 5 }, initializeArrayAtTimeOfDeclarationMethod3());
+    }
+
+    @Test
+    public void whenInitializeArrayUsingArraysFill_thenCorrect() {
+        assertArrayEquals(new long[] { 30, 30, 30, 30, 30 }, initializeArrayUsingArraysFill());
+    }
+
+    @Test
+    public void whenInitializeArrayRangeUsingArraysFill_thenCorrect() {
+        assertArrayEquals(new int[] { -50, -50, -50, 0, 0 }, initializeArrayRangeUsingArraysFill());
+    }
+
+    @Test
+    public void whenInitializeArrayRangeUsingArraysCopy_thenCorrect() {
+        assertArrayEquals(new int[] { 1, 2, 3, 4, 5 }, initializeArrayUsingArraysCopy());
+    }
+
+    @Test
+    public void whenInitializeLargerArrayRangeUsingArraysCopy_thenCorrect() {
+        assertArrayEquals(new int[] { 1, 2, 3, 4, 5, 0 }, initializeLargerArrayUsingArraysCopy());
+    }
+
+    @Test
+    public void whenInitializeLargerArrayRangeUsingArraysSetAll_thenCorrect() {
+        assertArrayEquals(new int[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, initializeArrayUsingArraysSetAll());
+    }
+}