如何制作不同长度的随机二维锯齿状数组？

Question

I have to create a 2D jagged array with a random number of rows (5-10) with each row having a random length (5-10). I filled the jagged array with random numbers. It should look something like this:

2 4 1 5 3 8 6 3 

2 5 8 9 7 4 3 5 6 

6 7 9 3 5

2 6 7 8 4 5 3 6 7

1 4 2 2 1

This is my current createArray method

 public static int [][] createArray(){
   int row = (int)(Math.random()*5)+5; 
   int column = (int)(Math.random()*5)+5;

   int[][]array = new int[row][];

   for(int i = 0; i < array.length; i++){
      for(int j = 0; j < array[i].length; j++){
        //Fill the matrix with random numbers
        array[i][j] = (int)(Math.random()*10);     
      }}  

   return array;    
  }//End createArray method

However, this just randomizes the rows and columns and doesn't create a jagged array. Can anyone help lead me in the right direction? Thanks a lot!

Answer 1

As @DoubleDouble stated, your code throws a NullPointerException .

It looks like you want something like this:

public static int [][] createArray(){
   int row = (int)(Math.random()*5)+5; 
   //int column = (int)(Math.random()*5)+5; //not needed

   int[][] array = new int[row][];

   for(int i = 0; i < array.length; i++){

      int column = (int)(Math.random()*5)+5; //create your random column count on each iteration
      array[i] = new int[column]; //Initialize with each random column count

      for(int j = 0; j < array[i].length; j++){
        //Fill the matrix with random numbers
        array[i][j] = (int)(Math.random()*10);   
      }
   }  

   return array;    
  }//End createArray method

Of course it will produce different results each time it runs, but here is a sample of what it will output:

1 2 5 4 3 9 2 7 9 
4 1 4 2 2 6 
9 5 7 8 7 8 4 2 
8 3 8 7 9 4 0 
0 2 1 4 9 3 7 8 
4 0 3 8 3 
1 3 8 9 9 8 

Answer 2

package JavaPrograms;
import java.util.Random;
public class jaggedarr
{
    public static void main(String[] args) {
        int a[][] = new int[3][];
        Random r = new Random();
        a[0] = new int[4];
        a[1] = new int[2];
        a[2] = new int[3];
        for (int[] a1 : a)
        {
            for (int j = 0; j < a1.length; j++)
            {
                a1[j] = r.nextInt(20);
            }
        }
        for(int i[] : a)
        {
            for(int j : i)
            {
                System.out.print(j + " ");
            }
            System.out.println("");
        }
    }
}