How to Fix the Array Index Out Of Bounds Exception in Java

The ArrayIndexOutOfBoundsException is a runtime exception in Java that occurs when an array is accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.

Since the ArrayIndexOutOfBoundsException is an unchecked exception, it does not need to be declared in the throws clause of a method or constructor.

What Causes ArrayIndexOutOfBoundsException

The ArrayIndexOutOfBoundsException is one of the most common errors in Java. It occurs when a program attempts to access an invalid index in an array i.e. an index that is less than 0, or equal to or greater than the length of the array.

Since a Java array has a range of [0, array length - 1], when an attempt is made to access an index outside this range, an ArrayIndexOutOfBoundsException is thrown.

ArrayIndexOutOfBoundsException Example

Here is an example of a ArrayIndexOutOfBoundsException thrown when an attempt is made to retrieve an element at an index that falls outside the range of the array:

public class ArrayIndexOutOfBoundsExceptionExample {
    public static void main(String[] args) {
        String[] arr = new String[10]; 
        System.out.println(arr[10]);
    }
}

In this example, a String array of length 10 is created. An attempt is then made to access an element at index 10, which falls outside the range of the array, throwing an ArrayIndexOutOfBoundsException:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 10 out of bounds for length 10
    at ArrayIndexOutOfBoundsExceptionExample.main(ArrayIndexOutOfBoundsExceptionExample.java:4)

How to Fix ArrayIndexOutOfBoundsException

To avoid the ArrayIndexOutOfBoundsException, the following should be kept in mind:

• The bounds of an array should be checked before accessing its elements.
• An array in Java starts at index 0 and ends at index length - 1, so accessing elements that fall outside this range will throw an ArrayIndexOutOfBoundsException.
• An empty array has no elements, so attempting to access an element will throw the exception.
• When using loops to iterate over the elements of an array, attention should be paid to the start and end conditions of the loop to make sure they fall within the bounds of an array. An enhanced for loop can also be used to ensure this.

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