How to Initialize 2D Array in Java

1. Initialize 2D Array in Java Using the new Keyword and the for Loop
2. Initialize 2D Array in Java Without Using the Initializer

In this article, we will learn how to initialize a 2D array in Java. A 2D array is an array of one-dimensional arrays. The elements in a 2D array are arranged in rows and columns in the form of a matrix.

Initialize 2D Array in Java Using the new Keyword and the for Loop

In the code given below, we have a char array - table that is declared using the new keyword. The 2-dimensional array table has 3 rows and 3 columns.

All the elements in an array have their default values if no value is provided. In the case of an int type 2-dimensional array, the default value, 0, is assigned to each element. Since we have a char type 2-dimensional array, the default value will be null - \0.

To iterate through each element of a 2-dimensional array, we need to use nested for loops. We can visualize table like 3 individual arrays of length 3. The expression table[row].length denotes the number of columns, which is 3 in this case.

The expression '1' + row * 3 + col where we vary row and column between 0 and 2 gives us a character from 1 to 9. This method works only for this case where the row and column length is 3.

Later, we print the values of the 2-dimensional array in a matrix form, as shown in the code below.

public class Array {
  public static void main(String[] args) {
    char[][] table = new char[3][3];
    for (int row = 0; row < table.length; row++) {
      for (int col = 0; col < table[row].length; col++) {
        table[row][col] = (char) ('1' + row * 3 + col);
      }
    }

    for (int row1 = 0; row1 < table.length; row1++) {
      for (int col1 = 0; col1 < table[row1].length; col1++)
        System.out.print(table[row1][col1] + " ");
      System.out.println();
    }
  }
}

Output:

1 2 3 
4 5 6 
7 8 9 

Initialize 2D Array in Java Without Using the Initializer

The most common way to declare and initialize a 2-dimensional array in Java is using a shortcut syntax with an array initializer. Here using {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}, we enclose each row’s initialization list in its own set of braces.

The expression above describes that we have a 2-dimensional array with 3 rows and 3 columns. In this way, we have declared and initialized a 2-dimensional array in a single line of code. The 2-dimensional array is then printed using a nested for loop, as shown below.

public class Array {
  public static void main(String[] args) {
    int[][] arr = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    for (int row = 0; row < 3; row++) {
      for (int col = 0; col < 3; col++) System.out.print(arr[row][col] + " ");
      System.out.println();
    }
  }
}

Output:

1 2 3 
4 5 6 
7 8 9