NullPointerException in Java: Common Causes and Null Safety Patterns

My Java application crashes with NullPointerException in unexpected cases—even after supposedly initializing objects. What causes these NPEs and how do I prevent them?

My Java application crashes with NullPointerException in unexpected cases—even after supposedly initializing objects. What causes these NPEs and how do I prevent them? ✅ Explanation & Fix NPEs commonly arise from: • Accessing array elements that are null or index out of bounds • Passing null references into methods and dereferencing them immediately • Returning null from methods and then calling methods on the result Fixes: • Avoid returning null; consider returning Optional<T> instead. • Use Objects.requireNonNull() to enforce non-null arguments early. • Add explicit null checks before dereferencing: java Copy code if (obj != null) { obj.doSomething(); } • Initialize variables immediately (e.g. default values instead of null) or use Optional safely.