Core Java & JVM Memory Architecture: Static, Final, Heap & Stack Models

JVM Memory Architecture Explained

When a Java application starts, the Java Virtual Machine allocates runtime memory divided into five primary data areas:

1. Classloader Subsystem: Loads, links, and initializes .class bytecode files.
2. Method Area (Metaspace): Stores class-level structure, static variables, and runtime constant pool.
3. Heap Memory: Stores all instantiated objects. Divided into Young Generation (Eden, S0, S1) and Old (Tenured) Generation.
4. JVM Stack: Stores stack frames for active method invocations containing local primitive variables and object references.
5. PC Registers & Native Method Stacks: Track instruction execution addresses for each thread.

Static vs Final Keywords in Java

• `static`: Associates variable or method with the Class rather than individual instances. Allocated once in Method Area.
• `final`: Prevents mutation. When applied to variables, value cannot be reassigned; applied to methods, prevents overriding; applied to classes, prevents inheritance (e.g. java.lang.String).