Array Reference

[Mubeen Shaik]

Hi All,

Please explain me why this code is giving run time error.

  
class Array2
 
{
  public static void main(String[] array)
 
  {
int [][] scores = new int[2][];
   
int[][] number = new int[3][];
 
number[0] = new int[10];
 
number[0][0] = 99;
 
System.out.println(number[0][0]);  // This prints 99
 
scores[0][1] = number[0][0]; // This is giving run time error;

  }
 

}
 

[Ernest Friedman-Hill]

A 2-dimensional array in Java is really an array of 1-d arrays. When you initialize using new int[3][], you get an array of three pointers to int arrays; all of those pointers are null. In your example, you assign an int[] for number[0] to point to, but scores[0] is still null, hence the error when you try to access an element of the (nonexistent) array it points to.

[Mubeen Shaik]

Hi Ernest,

Thanks for the reply. I was confused with the arrays concept. Now it is clear.

I did the following :

scores[0] = new int[3];

// The above line of code will create three elements in scores[0]? --
// Is my java terminlogy is correct ? - Please suggest.


scores[0][1] = number[0][0]; // Correct ?

Thanks,
Mubeen.

[Ernest Friedman-Hill]

It will now work, and your terminology is correct.