打印3D阵列

Question

I am trying to print arrays before and after they are filled with user given inputs. Therefore, this would be the output if the given size is 3:

//user inputs values for first matrix

Before adding:

Array [0] =

Array [1] =

Array [2] =

//add user inputs

After adding:

Array [0] = row 0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix 

Array[1] = Array[2] =

//ask for inputs for second matrix

Before Adding

Array [0] = row 0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix 

Array[1] = Array[2] =

After adding

Array [0] = row 0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix 

Array[1] = row 0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix Array[2] = 

I wrote the following code to achieve this (In a class called ThreeDRayRunner):

public static void print(int [][][] array)
{
    for (int i=0; i<array.length; i++ )
    {
        for (int x=0; x<array[i].length;x++)
        {
            System.out.println();
            System.out.print("row "+ x);
            for (int j=0; j<array[i][x].length;j++)
            {
                    System.out.print (array[i][x][j]+ " ");
            }
        }
    }

However,I get the following error:

Exception in thread "main" java.lang.NullPointerException at ThreeDRay.print(ThreeDRay.java:13) at ThreeDRayRunner.main(ThreeDRayRunner.java:41)

Also, in the runner I ask the user to input the integer that will be stored in the 3D Array. To do this I ask for the size and print the 3D Array when is empty and after the given numbers are added. This is my code for that:

Scanner keyboard = new Scanner(in);

    out.print("How many matrices are you going to enter? ");
    int s = keyboard.nextInt();


    int[][][] d3= new int [s][][];

    for(int i = 0; i < S; i++)
    {
        out.print("What is the size of the matrix " + i + " ? ");
        int size = keyboard.nextInt();

        int[][] mat = new int[size][size];
        out.println();

        for(int r=0; r<mat.length; r++)
        {
            for(int c=0; c<mat[r].length; c++)
            {
                out.print("Enter a value for spot " + r + " - " + c );
               mat[r][c]=keyboard.nextInt();
            }
        }

       out.println("The array before setting mat at spot "+i);


       ThreeDRay.print(d3);

       d3[i] = mat;


        out.println("The array after setting mat at spot "+i);

       ThreeDRay.print(d3);

Answer 1

You are not instantiating the 2nd and 3rd dimensions of d3 Did you mean to do this line before your first print?

d3[i] = mat;

So it would look like this:

d3[i] = mat;

out.println("The array before setting mat at spot "+i);
ThreeDRay.print(d3);

Follow up:

It looks like you actually didn't want to set d3[i] before your first print. In that case make sure you 3 dimensions for d3 are all non-null since your print is going to print all of them and not only the one that you set to mat. Initialize your 2nd and 3rd dimensions (to 0) before you start.

int[][][] d3= new int [s][][];
for (int i=0; i < d3.length ;++i){
  d3[i] = new int[0][0];
}