Quick Answer

Prevent NPEs in Java applications.

Understanding the Issue

Occurs when trying to access methods/properties of null objects. Java 14+ provides more helpful error messages. Always validate objects before use.

The Problem

This code demonstrates the issue:

Java Error 
String str = null;
int length = str.length(); // Throws NPE

The Solution

Here's the corrected code:

Java Fixed 
// Solution 1: Defensive checks
if (str != null) {
    length = str.length();
}

// Solution 2: Optional (Java 8+)
Optional<String> opt = Optional.ofNullable(str);
length = opt.map(String::length).orElse(0);

// Solution 3: Objects.requireNonNull
String safeStr = Objects.requireNonNull(str, "str cannot be null");

Key Takeaways

Use proper null-checking and Optional for safety.