Java 2D数组学习

Question

I have this practice Java code that I'm trying to finish. The obvious problem is that when I try to print the array[1][2] , it returns null, so I'm thinking the array might be empty. How do I take the user input to put in the array?

import java.util.Scanner;
public class Studyone {


    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);
        int row = 13;
        int col = 25;
        String sentence;
        String sentence2;
        String [][] map = new String[row][col];
        for (int i = 0; i < map.length; i++) 
        {
            for (int j = 0;i < map.length; i++) 
            {
                System.out.println("Enter the element");
                sentence2 = input.nextLine();
                map[i][j]=sentence2;
                if (row>col)
                {
                    break;
                }
            }
        }
        System.out.println(map[1][2]);
    }
}

Answer 1

Change

for (int j = 0;i < map.length; i++) 

to

for (int j = 0;j < map[0].length; j++) 

For example , suppose x = new int[3][4] , x[0] , x[1] , and x[2] are one-dimensional arrays and each contains four elements, as shown in the figure x.length is 3 , and x[0].length , x[1].length , and x[2].length are 4

Answer 2

This should help, i think:

for (int i = 0; i < map.length; i++) 
{
    for (int j = 0;j < map[i].length; j++) 
    {
        System.out.println("Enter the element");
        sentence2 = input.nextLine();
        map[i][j]=sentence2;
     }
}

Answer 3

• You are incrementing and checking condition for i instead of j in inner loop.
• Use map[i].length condition for inner loop

So your inner loop should be

for (int j = 0; j < map[i].length; j++)
                ^1      ^2         ^3

As first will increment i twice and for col you have to consider array of one dimension but you are considering map which may lead to ArrayIndexOutOfBoundException .

Here map[i][j]=sentence2; j will remain zero

I changed it, but the input just keeps going on and on non-stop.

It will as you have 13 rows and 25 columns so it will take time to insert all the values.So, just change(reduce) size of array and try.

Answer 4

change

for (int j = 0;i < map.length; i++)

to

for (int j = 0;j < map[i].length; j++)

Answer 5

Amend your code to the following:

for (int j = 0;i < map.length; i++)

to

for (int j = 0;i < map[j].length; j++)