How to print multi-dimensional arrays in Java

In Java, printing an array is a common task. Although, outputting the content of a one-dimensional array is straightforward enough, doing it for the content of a multi-dimensional array is more complex.

To print a multi-dimensional array, you first need to convert its content to a String using nested loops. The code below prints arrays of different dimensions.

class Main {
    public static void main( String args[] ) {
      
      // 1-D array
      int[] arr = {0, 1, 2, 3, 4}; 
      // 2-D array
      int[][] matrix = {
          {0, 1, 2}, {2, 3, 4}, {5, 6, 7}
        }; 
      
      // 3-D array
      int[][][] multiDimArray= { 
          { 
            {0, 1}, {2, 3}, {3, 4} 
          }, 
          { 
            {5, 6}, {7, 8}, {8, 9}
          }
        };
      System.out.print("1-D Array: \n[");
      // printing a 1-D array using loop
      for (int n: arr) {  
          System.out.print(n + " "); // printing each item
      }
      System.out.println("]\n");
      System.out.print("2-D Array: \n[");
      // printing a 2-D array using two nested loops
      for (int[] array: matrix) { 
        System.out.print("[");
        for (int n: array) {  
          System.out.print(n + " "); // printing each item
        }
        System.out.print("]"); // printing new line
      }
      System.out.println("]\n");
      System.out.println("3-D Array: ");
      // printing a 3-D array using three nested loops
      for (int[][] m: multiDimArray) { 
        System.out.print("[");
        for (int[] a: m) {
          System.out.print("[");
          for (int n: a) { 
            System.out.print(n + " "); // printing each item
          }
          System.out.print("]"); 
        } 
        System.out.print("]");     
      }
      System.out.println("]");
    }
}

We need to use the number of nested loops to iterate on each item of an N-dimensional array before printing it. As the number of dimensions increases, the code becomes more complex and harder to maintain.

However, there is a cleaner approach for this using the Arrays.toString() and Arrays.deepToString() library methods defined within the java.util.Arrays class.

To print a one-dimensional array, you need to call the Arrays.toString() method and pass the array as an argument. However, this only works with one-dimensional arrays.

To print a multi-dimensional array, you instead need to call the Arrays.deepToString() method and pass the multi-dimensional array as an argument.

See the code example below for more clarity on this:

import java.util.Arrays;
class Main {
    public static void main( String args[] ) {
      
      // 1-D array
      int[] arr = {0, 1, 2, 3, 4}; 
      // 2-D array
      int[][] matrix = {{0, 1, 2}, {2, 3, 4}, {5, 6, 7}}; 
      
      // 3-D array
      int[][][] multiDimArray= { 
        { 
          {0, 1}, {2, 3}, {3, 4} 
        }, 
        { 
          {5, 6}, {7, 8}, {8, 9}
        }
      };
      
      System.out.println("1-D Array: ");
      // printing a 1-D array using Arrays.toString
      System.out.println(Arrays.toString(arr));
      System.out.println("\n2-D Array: ");
      // printing a 2-D array using Arrays.deepToString
      System.out.println(Arrays.deepToString(matrix));
      System.out.println("\n3-D Array: ");
      // printing a 3-D array using Arrays.deepToString
      System.out.println(Arrays.deepToString(multiDimArray));
    }
}

Conclusion

You cannot print an array in Java just by using System.out.println(). Instead, you need to loop through each item and convert it to String before printing it.

A cleaner approach would be to use the appropriate utility method from the java.util.Arrays class. To print the content of a one-dimensional array, use the Arrays.toString() method. To print the content of a a multi-dimensional array, use the Arrays.deepToString() method.

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