How to fill a two Dimensional ArrayList in java with Integers?

Question

I have to create a 2d array with unknown size. So I have decided to go with a 2d ArrayList the problem is I\'m not sure how to initialize such an array or store information.

Answer 1

List> array = new ArrayList>();
// add row:
array.add( new ArrayList() );
// add a column:
array.get( array.size() -1 ).add( 1 );

Working demo:

import java.util.*;
import static java.lang.System.out;
class Load { 
    public static void main( String ... args ) { 

        List> array = new ArrayList>();

        Scanner input = new Scanner(System.in);
        out.println("Enter n:");
        int n = input.nextInt();

        out.println("Enter m:");
        int m = input.nextInt();

        out.println("Enter the values:");

        for( int i = 0 ; i < n ; i++ ) { 
            // add row:
            List list = new ArrayList();
            array.add( list );
            for( int j = 0 ; j < m ; j++ ) { 
                // add a column:
                // array.get( array.size() -1 ).add( 1 ); or
                list.add( input.nextInt() );
            }
        }
        out.println("Result:");
        out.println( array );

    }
}

Output:

C:\>java Load
Enter n:
3
Enter m:
6
Enter the values
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Result:
[[0, 1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11], [12, 13, 14, 15, 16, 17]]