how to build a 2D array using java by entering user-input?

Question

i have to build a 2D array that ask user to enter numbers to build the 2D array i know how to build this array using the for loop. But here i want to use the user input.

so anyone can help me ??

after i tried to run this program it display this error :

enter the elementss for the Matrix
Exception in thread "main" java.lang.NullPointerException
    at test7.test7.fill(test7.java:29)
    at test7.test7.main(test7.java:41)

this is my code:

package test7;

import java.util.Scanner;

public class test7 {

    private int row = 4;
    private int col = 4;
    private int[][] matrix;

    public test7(int trow, int tcol) {

        this.row = trow;
        this.col = tcol;
    }

    public test7(int trow, int tcol, int[][] m) {

        this.row = trow;
        this.col = tcol;
        this.matrix = m;
    }

    public int[][] fill(){

        System.out.println("enter the elementss for the Matrix");
        Scanner in = new Scanner(System.in);
        int[][] data = new int[0][0];
        for(int i = 0; i< matrix.length; i++){
            for(int j = 0 ;j< matrix[i].length; j++){
                int x = in.nextInt();
            }

        }
        return data;
    }

    public static void main(String[] args){

        Question2 q2 = new Question2(3, 2);
        q2.fill();
    }
}

The error is in your Question2 class. can you post the code of this class too?? — Syeda Zunaira
– Syeda Zunaira, Commented Dec 24, 2014 at 9:35
sorry i have changed the name of the package and the name of the class i edit my question..sorry again — java dev
– java dev, Commented Dec 24, 2014 at 9:39

Syeda Zunaira · Accepted Answer · 2014-12-24 09:55:36Z

1

Need to do this

   public static void main(String[] args){

    int[][] ma=new int[3][2];
    test7 q2 = new test7(3, 2,ma);
    q2.fill();
}

Instead of this

   public static void main(String[] args){

    Question2 q2 = new Question2(3, 2);
    q2.fill();
}

Reason

You are not initializing your matrix any where that is why getting the error.

edited Dec 24, 2014 at 9:55

answered Dec 24, 2014 at 9:50

Syeda Zunaira

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Comments

Rishi Rahiman · Accepted Answer · 2014-12-24 09:46:11Z

0

declare your int[][] data array with what size you want. try this:

public test7(int trow, int tcol) { this.row = trow; this.col = tcol; this.matrix = new int[trow][tcol]; }

answered Dec 24, 2014 at 9:46

Rishi Rahiman

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Comments

Muhammed Refaat · Accepted Answer · 2014-12-24 09:46:12Z

0

That's because you are declared matrix without initializing it : private int[][] matrix;, So, it's null now, as the constructor sets only the value of row and col, try to initialize it using the other constructor:

     Question2 q2 = new Question2(3, 2, new int[3][2]);

or give it the value in the first constructor execution:

public Question2(int trow, int tcol) {

    this.row = trow;
    this.col = tcol;
    this.matrix = new int[trow][tcol];
}

answered Dec 24, 2014 at 9:46

Muhammed Refaat

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