Common Pitfalls in Java Arrays

Arrays are powerful, but beginners often encounter mistakes when using them. Knowing these common pitfalls will help you write bug-free and efficient code.

1. ArrayIndexOutOfBoundsException

Occurs when you access an index that doesn’t exist in the array.

public class OutOfBoundsExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        System.out.println(numbers[3]); //  Error
    }
}

Error : Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3

2. Null Arrays

If an array reference points to null, any operation will throw a NullPointerException.

public class NullArrayExample {
    public static void main(String[] args) {
        int[] numbers = null;
        System.out.println(numbers.length); //  Error
    }
}

int[] numbers = new int[5]; // Correct

3. Choosing the Wrong Array Size

Arrays in Java have fixed sizes. Declaring a size too small can cause errors, too large wastes memory.

int[] scores = new int[3]; // Can only store 3 elements
scores[3] = 50; //  OutOfBounds

4. Arrays vs Collections

Common mistake: Using arrays when a dynamic structure is needed, or using ArrayList when performance-critical.

5. Mixing Types

Arrays can only store a single data type. Trying to mix types leads to compilation errors.

Object[] arr = {1, "Java", true}; //  Possible with Object array
int[] numbers = {1, "2"};        //  Error

Tips to Avoid Common Pitfalls

• Always check array bounds.
• Initialize arrays before use.
• Use numbers.length to control loops.
• Choose arrays for fixed-size, primitive-heavy data.
• Prefer Collections for dynamic and object-heavy data.
• Avoid mixing incompatible types.