ArrayIndexOutOfBoundsException in Java — Fix (2026) | Tutorials Logic

What is This Error?

The ArrayIndexOutOfBoundsException is thrown when you try to access an array element using an index that is either negative or greater than or equal to the array's length. Java arrays are zero-indexed, so valid indices are 0 to array.length - 1.

Error Message:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5

Common Causes

Using array.length instead of array.length - 1 as the last index
Off-by-one error in loop conditions
Accessing a negative index
Hardcoded index that doesn't match array size
Empty array with index access

Quick Fix (TL;DR)

Quick Solution

int[] arr = {10, 20, 30, 40, 50}; // length = 5

// ❌ Problem — index 5 doesn't exist
System.out.println(arr[5]); // Valid: 0-4 only!

// ✅ Solution — use length - 1 for last element
System.out.println(arr[arr.length - 1]); // 50

// ✅ Always check bounds before accessing
if (index >= 0 && index < arr.length) {
    System.out.println(arr[index]);
}

Common Scenarios & Solutions

Scenario 1: Off-by-One in Loop

Problem

int[] numbers = {1, 2, 3, 4, 5};
for (int i = 0; i <= numbers.length; i++) { // ❌ <= should be <
    System.out.println(numbers[i]); // Fails when i = 5!
}

Solution

int[] numbers = {1, 2, 3, 4, 5};

// ✅ Use < (strictly less than)
for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

// ✅ Or use enhanced for loop (no index needed)
for (int num : numbers) {
    System.out.println(num);
}

Scenario 2: Empty Array Access

Problem

int[] arr = new int[0]; // Empty array
System.out.println(arr[0]); // ArrayIndexOutOfBoundsException!

Solution

int[] arr = new int[0];

// ✅ Check length before accessing
if (arr.length > 0) {
    System.out.println(arr[0]);
} else {
    System.out.println("Array is empty");
}

Scenario 3: 2D Array Access

Problem

int[][] matrix = {{1, 2}, {3, 4}, {5, 6}};
for (int i = 0; i <= matrix.length; i++) {
    for (int j = 0; j <= matrix[i].length; j++) { // ❌ Both <= wrong!
        System.out.print(matrix[i][j]);
    }
}

Solution

int[][] matrix = {{1, 2}, {3, 4}, {5, 6}};
for (int i = 0; i < matrix.length; i++) {       // ✅ <
    for (int j = 0; j < matrix[i].length; j++) { // ✅ <
        System.out.print(matrix[i][j] + " ");
    }
    System.out.println();
}

Scenario 4: ArrayList vs Array

Solution

// ✅ Use ArrayList for dynamic sizing
List list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));

// Safe access with bounds check
int index = 10;
if (index >= 0 && index < list.size()) {
    System.out.println(list.get(index));
}

// ✅ Use streams for safe operations
OptionalInt first = IntStream.of(1, 2, 3).findFirst();
first.ifPresent(System.out::println);

Best Practices to Avoid This Error

Use enhanced for loops - Eliminates index management entirely
Always use < not <= in loop conditions - Standard pattern for array iteration
Check array length before access - Especially for dynamic data
Use ArrayList for dynamic collections - Avoids fixed-size limitations
Use Arrays.stream() for safe operations - Functional approach avoids index errors
Validate input indices - Check bounds before using user-provided indices
Use Collections.unmodifiableList() - Prevents accidental modification