printing out a 2-D array in Matrix format

Question

How can I print out a simple int [][] in the matrix box format like the format in which we handwrite matrices in. A simple run of loops doesn\'t apparently work. If it helps

Answer 1

Here's my efficient approach for displaying 2-D integer array using a StringBuilder array.

public static void printMatrix(int[][] arr) {
    if (null == arr || arr.length == 0) {
        // empty or null matrix
        return;
    }

    int idx = -1;
    StringBuilder[] sbArr = new StringBuilder[arr.length];

    for (int[] row : arr) {
        sbArr[++idx] = new StringBuilder("(\t");

        for (int elem : row) {
            sbArr[idx].append(elem + "\t");
        }

        sbArr[idx].append(")");
    }

    for (int i = 0; i < sbArr.length; i++) {
        System.out.println(sbArr[i]);
    }
    System.out.println("\nDONE\n");
}

Answer 2

To properly format numbers in columns, it's best to use printf. Depending on how big are the max or min numbers, you might want to adjust the pattern "%4d". For instance to allow any integer between Integer.MIN_VALUE and Integer.MAX_VALUE, use "%12d".

public void printMatrix(int[][] matrix) {
    for (int row = 0; row < matrix.length; row++) {
        for (int col = 0; col < matrix[row].length; col++) {
            System.out.printf("%4d", matrix[row][col]);
        }
        System.out.println();
    }
}

Example output:

 36 913 888 908
732 626  61 237
  5   8  50 265
192 232 129 307

Answer 3

In java8 fashion:

import java.util.Arrays;

public class MatrixPrinter {

    public static void main(String[] args) {
        final int[][] matrix = new int[4][4];
        printMatrix(matrix);
    }

    public static void printMatrix(int[][] matrix) {
        Arrays.stream(matrix)
        .forEach(
            (row) -> {
                System.out.print("[");
                Arrays.stream(row)
                .forEach((el) -> System.out.print(" " + el + " "));
                System.out.println("]");
            }
        );
    }

}

this produces

[ 0  0  0  0 ]
[ 0  0  0  0 ]
[ 0  0  0  0 ]
[ 0  0  0  0 ]

but since we are here why not make the row layout customisable?

All we need is to pass a lamba to the matrixPrinter method:

import java.util.Arrays;
import java.util.function.Consumer;

public class MatrixPrinter {

    public static void main(String[] args) {
        final int[][] matrix = new int[3][3];

        Consumer<int[]> noDelimiter = (row) -> {
            Arrays.stream(row).forEach((el) -> System.out.print(" " + el + " "));
            System.out.println();
        };

        Consumer<int[]> pipeDelimiter = (row) -> {
            Arrays.stream(row).forEach((el) -> System.out.print("| " + el + " "));
            System.out.println("|");
        };

        Consumer<int[]> likeAList = (row) -> {
            System.out.print("[");
            Arrays.stream(row)
            .forEach((el) -> System.out.print(" " + el + " "));
            System.out.println("]");
        };

        printMatrix(matrix, noDelimiter);
        System.out.println();
        printMatrix(matrix, pipeDelimiter);
        System.out.println();
        printMatrix(matrix, likeAList);

    }

    public static void printMatrix(int[][] matrix, Consumer<int[]> rowPrinter) {
        Arrays.stream(matrix)
        .forEach((row) -> rowPrinter.accept(row));
    }

}

this is the result :

 0  0  0 
 0  0  0 
 0  0  0 

| 0 | 0 | 0 |
| 0 | 0 | 0 |
| 0 | 0 | 0 |

[ 0  0  0 ]
[ 0  0  0 ]
[ 0  0  0 ]

Answer 4

    int[][] matrix = {
        {1,2,3},
        {4,5,6},
        {7,8,9}
    };
    //use foreach loop as below to avoid IndexOutOfBoundException
    //need to check matrix != null if implements as a method
    //for each row in the matrix
    for (int[] row : matrix) {
        //for each number in the row
        for (int j : row) {
            System.out.print(j + " ");
        }
        System.out.println("");
    }

Answer 5

final int[][] matrix = {
  { 1, 2, 3 },
  { 4, 5, 6 },
  { 7, 8, 9 }
};

for (int i = 0; i < matrix.length; i++) {
    for (int j = 0; j < matrix[i].length; j++) {
        System.out.print(matrix[i][j] + " ");
    }
    System.out.println();
}

Produces:

1 2 3
4 5 6
7 8 9

Answer 6

public static void main(String[] args) 
        {
             int [] [] ar= 
                {
                        {12,33,23},
                        {34,56,75},
                        {14,76,89},
                        {45,87,20}

                };

I prefer using enhanced loop in Java

Since our ar is an array of array [2D]. So, when you iterate over it, you will first get an array, and then you can iterate over that array to get individual elements.

             for(int[] num: ar)
             {
                 for(int ele : num)
                 {
                 System.out.print(" " +ele);
                 }
                 System.out.println(" " );
             }

              }