ArrayIndexOutOfBounds

**SwEeTAcTioN** · 12-07-2009, 01:50 AM

So i need a little help with arrays. Why doesnt this program work. I pretty much did what it said on the sun tutorial.

All help appreciated:)

Java Code:

import java.io.*;

public class Array
{
 public static void main(String[] args)throws IOException
 {
  int[] num;
  num=new int[3];
  num[1]=4;
  num[2]=3;
  num[3]=2;
  System.out.println(num[1]);
 }
}

And my error is

Java Code:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
    at Array.main(Array.java:11)

**Fubarable** · 12-07-2009, 01:52 AM

arrays are 0 based. Thus your num int[3] array will go from:
num[0]
num[1]
num[2]

If you try to use
num[3] you'll go beyond the array's bounds.

**SwEeTAcTioN** · 12-07-2009, 01:55 AM

oh i didnt know that thanks man it works now:)

**travishein** · 12-07-2009, 01:56 AM

array 'indicies' are always zero based. at first this is confusing, because an array of three elements, and have indicies 0,1,2

in your example, the array index out of bounds exception would be occuring on

Java Code:

num[3]=2;

, because the array was defined to be three elements.

the general rule of thumb is the inxex in the [ ] is always (-1) from the physical element.

(because we as humans think of the first element in the array as the 1st element, not the 0th element).

So this code to work would then be.

Java Code:

public class Array
{
 public static void main(String[] args)throws IOException
 {
  int[] num;
  num=new int[3];
  num[0]=4;
  num[1]=3;
  num[2]=2;
  System.out.println(num[1]);
 }
}