NullPointerException During Unboxing

Why This Happens

Java auto-unboxes wrapper types like Integer to int automatically. When the wrapper is null, this unboxing triggers a NullPointerException. This is subtle because the code looks like a simple assignment, not a method call.

The Problem

Map<String, Integer> map = new HashMap<>();
int value = map.get("missing_key"); // NPE: unboxing null Integer

The Fix

Map<String, Integer> map = new HashMap<>();
Integer value = map.get("missing_key");
if (value != null) {
    int intValue = value;
}

Step-by-Step Fix

1. 1

   Identify the unboxing

   Look for assignments from wrapper types (Integer, Long, Boolean, Double) to primitive types (int, long, boolean, double).

2. 2

   Find the null source

   Check if the wrapper value could be null, especially from Map.get(), database queries, or method return values.

3. 3

   Use wrapper type or default value

   Use the wrapper type instead of the primitive, or provide a default with getOrDefault() or Optional.