https://jira.baeldung.com/browse/BAEL-9394 (#18706)

Author: Michaelin007

core-java-modules/core-java-arrays-multidimensional/src/main/java/com/baeldung/array/MultiDimensionalArray.java

@@ -18,15 +18,49 @@ int[][] declarationAndThenInitialization() {
         return multiDimensionalArray;
     }
 
+    int[][] declarationAndThenInitializationBaseOnIndex() {
+        int[][] multiDimensionalArray = new int[3][];
+        multiDimensionalArray[0] = new int[2];
+        multiDimensionalArray[1] = new int[3];
+        multiDimensionalArray[2] = new int[4];
+
+        multiDimensionalArray[0][0] = 1;
+        multiDimensionalArray[0][1] = 2;
+
+        multiDimensionalArray[1][0] = 3;
+        multiDimensionalArray[1][1] = 4;
+        multiDimensionalArray[1][2] = 5;
+
+        multiDimensionalArray[2][0] = 6;
+        multiDimensionalArray[2][1] = 7;
+        multiDimensionalArray[2][2] = 8;
+        multiDimensionalArray[2][3] = 9;
+
+        return multiDimensionalArray;
+    }
+
     int[][] declarationAndThenInitializationUsingUserInputs() {
         int[][] multiDimensionalArray = new int[3][];
         multiDimensionalArray[0] = new int[2];
         multiDimensionalArray[1] = new int[3];
         multiDimensionalArray[2] = new int[4];
+
         initializeElements(multiDimensionalArray);
         return multiDimensionalArray;
     }
 
+    int[][] declarationAndThenInitializationFirstAlternative() {
+        int[][] multiDimensionalArray = new int[][] { new int[] { 1, 2 }, new int[] { 3, 4, 5 }, new int[] { 6, 7, 8, 9 } };
+
+        return multiDimensionalArray;
+    }
+
+    int[][] declarationAndThenInitializationSecondAlternative() {
+        int[][] multiDimensionalArray = { new int[] { 1, 2 }, new int[] { 3, 4, 5 }, new int[] { 6, 7, 8, 9 } };
+
+        return multiDimensionalArray;
+    }
+
     void initializeElements(int[][] multiDimensionalArray) {
         Scanner sc = new Scanner(System.in);
         for (int outer = 0; outer < multiDimensionalArray.length; outer++) {
@@ -48,6 +82,15 @@ void printElements(int[][] multiDimensionalArray) {
         }
     }
 
+    void printElementsUsingNestedForLoop(int[][] multiDimensionalArray) {
+        for (int i = 0; i < multiDimensionalArray.length; i++) {
+            for (int j = 0; j < multiDimensionalArray[i].length; j++) {
+                System.out.print(multiDimensionalArray[i][j] + " ");
+            }
+            System.out.println();
+        }
+    }
+
     int[] getElementAtGivenIndex(int[][] multiDimensionalArray, int index) {
         return multiDimensionalArray[index];
     }
@@ -62,8 +105,8 @@ int[] findLengthOfElements(int[][] multiDimensionalArray) {
 
     Integer[] findLengthOfElements(Integer[][] multiDimensionalArray) {
         return Arrays.stream(multiDimensionalArray)
-          .map(array -> array.length)
-          .toArray(Integer[]::new);
+            .map(array -> array.length)
+            .toArray(Integer[]::new);
     }
 
     int[][] copy2DArray(int[][] arrayOfArrays) {
@@ -77,7 +120,7 @@ int[][] copy2DArray(int[][] arrayOfArrays) {
 
     Integer[][] copy2DArray(Integer[][] arrayOfArrays) {
         return Arrays.stream(arrayOfArrays)
-          .map(array -> Arrays.copyOf(array, array.length))
-          .toArray(Integer[][]::new);
+            .map(array -> Arrays.copyOf(array, array.length))
+            .toArray(Integer[][]::new);
     }
 }

core-java-modules/core-java-arrays-multidimensional/src/test/java/com/baeldung/array/MultiDimensionalArrayUnitTest.java

@@ -46,7 +46,21 @@ public void givenMultiDimensionalArray_whenUsingArraysAPI_thenVerifyPrintedEleme
         ByteArrayOutputStream outContent = new ByteArrayOutputStream();
         System.setOut(new PrintStream(outContent));
         obj.printElements(multiDimensionalArr);
-        assertEquals("[1, 2][3, 4, 5][6, 7, 8, 9]", outContent.toString().replace("\r", "").replace("\n", ""));
+        assertEquals("[1, 2][3, 4, 5][6, 7, 8, 9]", outContent.toString()
+            .replace("\r", "")
+            .replace("\n", ""));
+        System.setOut(System.out);
+    }
+
+    @Test
+    public void givenMultiDimensionalArray_whenUsingNestedForLoopToPrint_thenVerifyPrintedElements() {
+        int[][] multiDimensionalArr = { { 1, 2 }, { 3, 4, 5 }, { 6, 7, 8, 9 } };
+        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+        System.setOut(new PrintStream(outContent));
+        obj.printElementsUsingNestedForLoop(multiDimensionalArr);
+        assertEquals("1 2 3 4 5 6 7 8 9 ", outContent.toString()
+            .replace("\r", "")
+            .replace("\n", ""));
         System.setOut(System.out);
     }
 
@@ -57,27 +71,27 @@ public void givenMultiDimensionalArray_whenUsingArraysFill_thenVerifyInitialize2
         multiDimensionalArr[1] = new int[3];
         multiDimensionalArr[2] = new int[4];
         obj.initialize2DArray(multiDimensionalArr);
-        assertArrayEquals(new int[][] {{7,7}, {7,7,7}, {7,7,7,7}}, multiDimensionalArr);
+        assertArrayEquals(new int[][] { { 7, 7 }, { 7, 7, 7 }, { 7, 7, 7, 7 } }, multiDimensionalArr);
     }
-    
+
     @Test
     public void givenMultiDimensionalArray_whenUsingIteration_thenVerifyFindLengthOfElements() {
         int[][] multiDimensionalArr = { { 1, 2 }, { 3, 4, 5 }, { 6, 7, 8, 9 } };
-        assertArrayEquals(new int[]{2,3,4}, obj.findLengthOfElements(multiDimensionalArr));
+        assertArrayEquals(new int[] { 2, 3, 4 }, obj.findLengthOfElements(multiDimensionalArr));
     }
-    
+
     @Test
     public void givenMultiDimensionalArray_whenUsingArraysStream_thenVerifyFindLengthOfElements() {
         Integer[][] multiDimensionalArr = { { 1, 2 }, { 3, 4, 5 }, { 6, 7, 8, 9 } };
-        assertArrayEquals(new Integer[]{2,3,4}, obj.findLengthOfElements(multiDimensionalArr));
+        assertArrayEquals(new Integer[] { 2, 3, 4 }, obj.findLengthOfElements(multiDimensionalArr));
     }
-    
+
     @Test
     public void givenMultiDimensionalArray_whenUsingArraysCopyOf_thenVerifyCopy2DArray() {
         int[][] multiDimensionalArr = { { 1, 2 }, { 3, 4, 5 }, { 6, 7, 8, 9 } };
         assertArrayEquals(multiDimensionalArr, obj.copy2DArray(multiDimensionalArr));
     }
-    
+
     @Test
     public void givenMultiDimensionalArray_whenUsingArraysStream_thenVerifyCopy2DArray() {
         Integer[][] multiDimensionalArr = { { 1, 2 }, { 3, 4, 5 }, { 6, 7, 8, 9 } };