Quick Answer

Handle invalid array access.

Understanding the Issue

This runtime exception occurs when accessing an array with an invalid index (negative or ? array length).

The Problem

This code demonstrates the issue:

Java Error 
int[] arr = new int[5];
int val = arr[5]; // Throws

The Solution

Here's the corrected code:

Java Fixed 
// Check bounds:
int index = 5;
if (index >= 0 && index < arr.length) {
    val = arr[index];
}

// Enhanced for-loop (avoids indexes):
for (int num : arr) {
    // Safe iteration
}

// Use List instead:
List<Integer> list = Arrays.asList(1, 2, 3);
if (index < list.size()) {
    val = list.get(index);
}

// Java 9+:
OptionalInt val = Arrays.stream(arr)
    .skip(index)
    .findFirst();

Key Takeaways

Always validate array indices before access.