Memory Areas in JVM

JVM uses runtime memory areas to organize code, objects, and thread execution.

Total 5 Main Memory Areas

1. Method Area
2. Heap Area
3. Stack Area
4. PC Register
5. Native Method Stack (Native Method Area)

1. Method Area

Stores class-level metadata loaded by class loader.

Data typically stored

• .class structure information
• Runtime constant pool
• Method metadata
• Static variables

From your notes point of view:

• .class file information
• static variables

2. Heap Area

Stores all objects and arrays created during runtime.

Data typically stored

• Objects
• Arrays
• Instance variables (as part of objects)

This is shared by all threads and managed by garbage collector.

3. Stack Area

Each thread has its own JVM stack.

Data typically stored per stack frame

• Current running method context
• Local variables
• Operand stack
• Return information

From your notes point of view:

• Current running methods
• Local variables

4. PC (Program Counter) Register

Each thread keeps a PC register holding address of current JVM instruction being executed.

5. Native Method Stack

Used when Java code calls native (non-Java) methods via JNI.

Memory Areas Quick Table

Typical Interview Questions

Q: What data is stored in Method Area?
Class information and static variables.

Q: What data is stored in Heap Area?
Objects, arrays, and object instance state.

Q: What data is stored in Stack Area?
Current running method frames and local variables.