Memory Management

Java manages memory automatically, but knowing how it works distinguishes a junior developer from a senior one.

Stack vs Heap

JVM memory is primarily divided into two parts:

1. Stack Memory

• What it stores: Local variables (primitives) and method call details (order of execution).
• Characteristics: Fast access. LIFO (Last-In-First-Out).
• Scope: Data is removed as soon as the method execution completes.

2. Heap Memory

• What it stores: Objects (anything created with new) and instance variables.
• Characteristics: Slower than Stack. Used for dynamic memory allocation.
• Scope: Objects stay until they are no longer referenced.

Garbage Collection (GC)

In languages like C++, you must delete objects manually. Java does this for you!

The Garbage Collector is a background process looking for objects in the Heap that are no longer referenced by any part of your program (unreachable objects) and deletes them to free up memory.

When does GC run?

It runs automatically, but determining exactly when is up to the JVM. You can request it via System.gc(), but execution is not guaranteed.

Memory Leaks in Java

Wait, if we have GC, can we have leaks? Yes. If you keep static references to unused objects, the GC thinks they are still in use and won't delete them.

Quiz

Next Steps

Now you know how Java thinks. It's time to learn the most important paradigm: Object-Oriented Programming (OOP).