This java.lang.ArrayIndexOutOfBoundsException is thrown when we are accessing an array with an index which is greater than the size of an array.

P.S Array index starts with 0

package com.mkyong;

public class ArrayExample {

 public static void main(String[] args) {

 // array of 3
 int[] num = new int[3];

 num[0] = 1;
 num[1] = 2;
 num[2] = 3;
 num[3] = 4; //ArrayIndexOutOfBoundsException: 3

 System.out.println("num[0] : " + num[0]);
 System.out.println("num[1] : " + num[1]);
 System.out.println("num[2] : " + num[2]);
 System.out.println("num[3] : " + num[3]); //ArrayIndexOutOfBoundsException: 3

 }

}

Output

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
	at com.mkyong.calculator.ArrayExample.main(ArrayExample.java:13)

References

• Java – How to declare and initialize an Array
• ArrayIndexOutOfBoundsException