Java Language ArrayIndexOutOfBoundsException


Example

The ArrayIndexOutOfBoundsException is thrown when a non-existing index of an array is being accessed.

Arrays are zero-based indexed, so the index of the first element is 0 and the index of the last element is the array capacity minus 1 (i.e. array.length - 1).

Therefore, any request for an array element by the index i has to satisfy the condition 0 <= i < array.length, otherwise the ArrayIndexOutOfBoundsException will be thrown.


The following code is a simple example where an ArrayIndexOutOfBoundsException is thrown.

String[] people = new String[] { "Carol", "Andy" };

// An array will be created:
// people[0]: "Carol"
// people[1]: "Andy"

// Notice: no item on index 2. Trying to access it triggers the exception:
System.out.println(people[2]);  // throws an ArrayIndexOutOfBoundsException.

Output:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2
    at your.package.path.method(YourClass.java:15)

Note that the illegal index that is being accessed is also included in the exception (2 in the example); this information could be useful to find the cause of the exception.


To avoid this, simply check that the index is within the limits of the array:

int index = 2;
if (index >= 0 && index < people.length) {
    System.out.println(people[index]);
}