NegativeArraySizeException

Why This Happens

Java does not allow arrays with negative lengths. This exception is thrown when you pass a negative value as an array size. It usually occurs when a size variable comes from a calculation that unexpectedly produces a negative result or from unvalidated user input.

The Problem

int size = list1.size() - list2.size(); // Could be negative
int[] result = new int[size]; // NegativeArraySizeException if size < 0

The Fix

int size = Math.max(0, list1.size() - list2.size());
int[] result = new int[size];

Step-by-Step Fix

1. 1

   Identify the array creation

   Find the new array allocation in the stack trace and check what value is being used as the size.

2. 2

   Trace the size value

   Follow the size variable to find why it became negative.

3. 3

   Validate the size

   Use Math.max(0, size) or throw a meaningful exception if a negative size indicates a logic error.