Java prints "null" while taking in array of strings as input from the user using Scanner and ends abruptly

Question

import java.util.Scanner;
class ArrayofArrays {
    public static void main(String[] args) {
        String[][] ListofNames = {
            {"barbie","cinderella","troomtroom"},
            {"wonderwoman","captainmarvel","Cheetah"}
        };
        for(String[] i : ListofNames) {
            for(String x: i) {
                System.out.println(x);
            }
        }
        int r,c;
        Scanner obj = new Scanner(System.in);
        System.out.println("Enter rows\n");
        r = obj.nextInt();
        System.out.println("Enter columns\n");
        c = obj.nextInt();
        String[][] Inputnames = new String[r][c];
        for(int j = 0;j<r;j++) {
            for(int l = 0;l<c;l++) {
                System.out.println("Enter name\n");
                Inputnames[j][l] = obj.nextLine();
            }
        for(int m = 0;m<r;m++) {
            for(int n = 0;n<c;n++) {
                System.out.println(Inputnames[m][n]);
                }
            }
        }
    }
}

I was learning java and when I tried to to take in Array of Arrays consisting of strings as user input, it printed out null and didnt take further inputs. What am I missing out?

The output is like this on the cmd:

C:\Users\dynam\Desktop\Java Files>java ArrayofArrays barbie cinderella troomtroom wonderwoman captainmarvel Cheetah Enter rows

2 Enter columns

1 Enter name

null Enter name

batman

What was the full output of the program, include it in the question. — Kayaman, Jul 02 '20 at 05:32

score 1 · Answer 1 · answered Jul 02 '20 at 05:40

I've seen this happen a lot in several questions. The issue is described here more in detail.

To fix your issue, replace the obj.nextInt() with Integer.parseInt(obj.nextLine()). So basically your code should look like the following:

    System.out.println("Enter rows\n");
    r = Integer.parseInt(obj.nextLine());
    System.out.println("Enter columns\n");
    c = Integer.parseInt(obj.nextLine());

If by any chance your will enter something else than an integer here, you might have to use a try-catch block to make sure you deal with NumberFormatExceptions.

Thanks,this solved it.I cannot upvote as I dont have enough "reputation". — Savannah Madison, Jul 02 '20 at 05:47

score 1 · Accepted Answer · answered Jul 02 '20 at 05:48

Because the Scanner.nextInt method does not read the newline character in your input created after pressing "Enter," and so the call to Scanner.nextLine returns after reading that new line.

Also Looks like your for loops are messed up, try the following code (cleaned up a bit)-

package com.example.demo;

import java.util.Scanner;

class ArrayofArrays {
    public static void main(String[] args) {
        String[][] ListofNames = {
                {"barbie", "cinderella", "troomtroom"},
                {"wonderwoman", "captainmarvel", "Cheetah"}
        };
        for (String[] i : ListofNames) {
            for (String x : i) {
                System.out.println(x);
            }
        }
        int r, c;
        Scanner obj = new Scanner(System.in);
        System.out.println("Enter rows\n");
        r = obj.nextInt();
        System.out.println("Enter columns\n");
        c = obj.nextInt();
        obj.nextLine();
        String[][] Inputnames = new String[r][c];
        for (int j = 0; j < r; j++) {
            for (int l = 0; l < c; l++) {
                System.out.println("Enter name\n");
                Inputnames[j][l] = obj.nextLine();

            }
        }
        for (int m = 0; m < r; m++) {
            for (int n = 0; n < c; n++) {
                System.out.println(Inputnames[m][n]);
            }
        }
    }
}

Hope this helps!

Thanks a ton,like you said,I had a mistake in the braces of my for loop.Now works. — Savannah Madison, Jul 02 '20 at 05:55
Additionally, you should close your scanner at the end to prevent resource leaks. — maloomeister, Jul 02 '20 at 07:18

Java prints "null" while taking in array of strings as input from the user using Scanner and ends abruptly

2 Answers2