具有用户输入和随机数的2D数组

Question

I am trying to generate a program that ask the user a number "n" and displays a 2 xn array. Eg:

1 2 3 4 5 (User input)

5 8 2 1 5 (Random numbers)

I can't see to make my code to work. Here is my code:

import java.util.Scanner;


public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {



        Scanner input = new Scanner(System.in);
        System.out.print("Enter number of exits: ");
        int n = input.nextInt();

        int [][] A = new int[2][n];
        for (int i =0; i <= A[n].length; i++){

            A[i][n]= (int)(Math.random()*10);
    }
        System.out.println(A[2][n]);
        System.out.print("Distance between exit i and exit j is: " + distance());
    }



    public static int distance(){
        Scanner input = new Scanner(System.in);

        System.out.print("Please enter exit i: ");
        int i = input.nextInt();
        System.out.print("Please enter exit j: ");
        int j = input.nextInt();
        return i + j;
    }
}

I am getting this error

"Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5"

How can I fix it? And I think my Math.random is wrong. Can you guys help me with some advises or where am I doing things wrong? Thanks.

Answer 1

All your errors lie within and after your for-loop:

for (int i =0; i <= A[n].length; i++){

        A[i][n]= (int)(Math.random()*10);
}

If n = 5, A[5].length does not exist, because the first dimensions of your array only exist between 0 and 1. A[2] reserves space for 2 int primitives, the first is at index 0 and the last is at index 1. Even if that is changed, the i variable your for loop declares is incremented beyond 1 and so the JVM will throw a ArrayIndexOutOfBoundsException.

When declaring an array with the dimensions [2][n], (given n is an Integer, which will be provided by the user via the scanner) you cannot access arrayReference [2][x]

Arrays are based on a 0 index structure ...

Consider the following:

int [][] A = new int[2][2];

You can only access A[0][0], A[0][1], A[1][0] & A[1][1].

you CANNOT access A[2][0], A[2][1] or A[2][2].

---

Here's what you need to do:

 //A.length will give you the length of the first dimension (2)
 for(int i=0; i<A.length; i++){
            for(int j=0; j<n; j++){
                A[i][j] = (int) (Math.random()*10);
            }
        }
    }
 System.out.println(A[1][n-1]);
 System.out.print("Distance between exit i and exit j is: " + distance());