Java - Two Dimensional Arrays - Java - DYclassroom

In this tutorial we will learn about Two Dimensional Arrays in Java programming language.

We use two dimensional, 2D array to store data in rows and columns format.

Declaring a 2D array

Following is the syntax to declare a 2D array.

dataType[][] arrayName;

Where, name of the array variable is arrayName and its data type is dataType.

We can also declare 2D array in the following manner.

dataType arrayName[][];

This is similar to C programming language.

In the following example we are declaring a 2D array arr of data type int to store integer values.

int[][] arr;

Now, lets go ahead and create a 2D array.

Creating a 2D array

To create a 2D array we use the new keyword as shown below.

arrayName = new dataType[row_size][col_size];

Where, arrayName is the name of the array variable of data type dataType and it has row_size number of rows and col_size number of columns.

In the following example we are creating an array arr having 2 rows and 3 columns and of data type int.

arr = new int[2][3];

Declaration and Creation of 2D array

In the following example we are declaring and creating a 2D array arr of having 2 rows and 3 columns and of data type int.

int[][] arr = new int[2][3];

Assigning and Accessing value of a 2D array

In the following example we are creating a 2D array arr having 2 rows and 3 columns and of data type int.

To access the element of the array we are using the row-index and column-index like arr[r][c] to access element at r^th row and c^th column.

class Array2DExample {
  public static void main(String args[]) {
    // create an array
    int[][] arr = new int[2][3];

    // int variable
    int count = 1;
    
    // use for loop to assign value to an array
    for (int r = 0; r < 2; r++) {
      for (int c = 0; c < 3; c++) {
        arr[r][c] = count;
        count++;
      }
    }
    
    // print the value of the array
    for (int r = 0; r < 2; r++) {
      for (int c = 0; c < 3; c++) {
        System.out.print("arr[" + r + "][" + c + "] = " + arr[r][c] + " ");
      }
      System.out.println();
    }
  }
}

Output:

arr[0][0] = 1 arr[0][1] = 2 arr[0][2] = 3 
arr[1][0] = 4 arr[1][1] = 5 arr[1][2] = 6

Another way of assigning the values is by using {} curly brackets and using comman separated values.

class Array2DExample {
  public static void main(String args[]) {
    // create an array
    int[][] arr = {
      {1, 2, 3},
      {4, 5, 6}
    };
    
    // print the value of the array
    for (int r = 0; r < 2; r++) {
      for (int c = 0; c < 3; c++) {
        System.out.print("arr[" + r + "][" + c + "] = " + arr[r][c] + " ");
      }
      System.out.println();
    }
  }
}

We can even assign value index-wise like the following.

class Array2DExample {
  public static void main(String args[]) {
    // create an array
    int[][] arr = new int[2][3];
    
    // assign value to 1st row having r-index 0
    arr[0][0] = 1;
    arr[0][1] = 2;
    arr[0][2] = 3;
    
    // assign value to 2nd row having r-index 1
    arr[1][0] = 4;
    arr[1][1] = 5;
    arr[1][2] = 6;
    
    // print the value of the array
    for (int r = 0; r < 2; r++) {
      for (int c = 0; c < 3; c++) {
        System.out.print("arr[" + r + "][" + c + "] = " + arr[r][c] + " ");
      }
      System.out.println();
    }
  }
}

Representation of 2D array

The following image depicts a 2D array arr.

// array having 2 rows and 3 columns
int[][] arr = {
      {1, 2, 3},
      {4, 5, 6}
    };

Example #1: Write a Java program to find the average score of two students in three papers

Given, score of first student is 60, 55 and 70 while score of the second student is 80, 60 and 41.

We can store the score of the two students in a 2D array having 2 rows and 3 columns. The rows will represent the student and the columns will hold the score of the students.

class Array2DExample {
  public static void main(String args[]) {
    // create an array
    int[][] score = {
      {60, 55, 70},
      {80, 60, 41}
    };

    // sum array
    int[] sum = new int[2];

    // sum of 1st student
    sum[0] = 0;

    // sum of 2nd student
    sum[1] = 0;

    // average array
    float[] avg = new float[2];
    
    // compute sum
    for (int r = 0; r < 2; r++) {
      for (int c = 0; c < 3; c++) {
        sum[r] += score[r][c];
      }
    }
    
    // compute average of 1st student
    avg[0] = (float)sum[0] / 3;
    
    // compute average of 2nd student
    avg[1] = (float)sum[1] / 3;

    // print result
    System.out.println("Average score of 1st student = " + avg[0]);
    System.out.println("Average score of 2nd student = " + avg[1]);
  }
}