Jagged Array in Java (original) (raw)

In Java, a Jagged array is a multidimensional array where each row can have a different number of columns. When we work with a jagged array, one thing to keep in mind is that the inner array can be of different lengths. It is like a 2D array, but each row can have a different number of elements.

Java `

class Geeks { public static void main(String[] args){

    // Declaring 2-D array with 2 rows
    int arr[][] = new int[2][];

    // Making the above array Jagged
    arr[0] = new int[3];
    arr[1] = new int[2];

    // Initializing array
    int count = 0;
    for (int i = 0; i < arr.length; i++)
        for (int j = 0; j < arr[i].length; j++)
            arr[i][j] = count++;

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

}

The image below demonstrates a Jagged array, where each row in a 2D array can have a different number of elements.

JaggedArray

Jagged Array representation

**Declaration and Initialization of Jagged Array

The declaration of Jagged array is:

data_type array_name[][] = new data_type[n][]; // n= no. of rows

array_name[0] = new data_type[n1] //n1= no. of columns in row-1
array_name[1] = new data_type[n2] //n2= no. of columns in row-2
array_name[2] = new data_type[n3] //n3= no. of columns in row-3
.
.
.
and so on

The Alternative ways to initialize a Jagged array is listed below:

****// Method 1**
int arr_name[][] = new int[][] {
new int[] {10, 20, 30 ,40},
new int[] {50, 60, 70, 80, 90, 100},
new int[] {110, 120}
};

****// Method 2**
int[][] arr_name = {
new int[] {10, 20, 30 ,40},
new int[] {50, 60, 70, 80, 90, 100},
new int[] {110, 120}
};

****// Method 3**
int[][] arr_name = {
{10, 20, 30 ,40},
{50, 60, 70, 80, 90, 100},
{110, 120}
};

More Examples of Jagged Array

**Example 1: Here row i has i + 1 columns.

Java `

class Geeks { public static void main(String[] args) { int r = 5;

    // Declaring 2-D array with 5 rows
    int arr[][] = new int[r][];

    // Creating a 2D array such that first row has 1 element, second row has two elements and so on
    for (int i = 0; i < arr.length; i++)
        arr[i] = new int[i + 1];

    // Initializing array
    int count = 0;
    for (int i = 0; i < arr.length; i++)
        for (int j = 0; j < arr[i].length; j++)
            arr[i][j] = count++;

    // Displaying the values of 2D Jagged array
    System.out.println("Contents of 2D Jagged Array");
  
    for (int i = 0; i < arr.length; i++) {
        for (int j = 0; j < arr[i].length; j++)
            System.out.print(arr[i][j] + " ");
        System.out.println();
    }
}

}

Output

Contents of 2D Jagged Array 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

**Explanation: In the above example, we are creating a jagged array where each row will get one more element than the previous one, suppose the first row has one element then the second row has two element and then the third row has three element and so on. It fills the array with numbers starting from 0 and then prints them

Example 2: User Input Jagged Array

Java `

import java.util.Scanner;

public class Geeks { public static void main(String[] args) {

    Scanner scan = new Scanner(System.in);
    
      System.out.print("Enter the number of sub-arrays: ");
    int numberOfArrays = scan.nextInt();
    
    // Declare the jagged array
    int[][] jaggedArray = new int[numberOfArrays][];
    
    // Allocate memory to each sub-array
    for (int i = 0; i < numberOfArrays; i++) {
        System.out.print("Enter the size of sub-array " + (i + 1) + ": ");
        int sizeOfSubArray = scan.nextInt();
        jaggedArray[i] = new int[sizeOfSubArray];
    }
    
    // Initialize the elements of each sub-array
    for (int i = 0; i < numberOfArrays; i++) {
        System.out.println("Enter the elements of sub-array " + (i + 1) + ":");
      
        for (int j = 0; j < jaggedArray[i].length; j++) {
            jaggedArray[i][j] = scan.nextInt();
        }
    }
    
    // Print the elements of the jagged array
    System.out.println("The jagged array is:");
    for (int i = 0; i < numberOfArrays; i++) {
        
          for (int j = 0; j < jaggedArray[i].length; j++) {
            System.out.print(jaggedArray[i][j] + " ");
        }
        System.out.println();
    }
    
    scan.close();
}

}

Input:

Enter the number of sub-arrays: 4
Enter the size of sub-array 1: 3
Enter the size of sub-array 2: 4
Enter the size of sub-array 3: 2
Enter the size of sub-array 4: 4

Enter the elements of sub-array 1:
1 2 3

Enter the elements of sub-array 2:
5 6 7 8

Enter the elements of sub-array 3:
6 7

Enter the elements of sub-array 4:
1 2 3 4

Output:

The jagged array is:
1 2 3
5 6 7 8
6 7
1 2 3 4

**Advantages

The advantages of using a jagged array is listed below:

With jagged array we can decide the size at runtime.
Jagged array saves memory because we only create space for what we actually needed.
Sometimes we have to work with data that has rows of different lengths, in that case we prefer using jagged array.
Jagged arrays are faster because we only store what we needed and that why accessing the data becomes faster.

**Note: Jagged arrays can make the code a bit harder to write and read, so it’s best to use them only when really needed.