What are the different types of memory areas in JVM

💡 Concept: JVM Memory Areas

JVM divides memory into several runtime areas such as Heap, Stack, Method Area, Program Counter, and Native Method Stack for efficient execution and management.

📘 Quick Intro

Each memory area serves a specific purpose in managing Java program execution and resource allocation.

🧠 Analogy

Think of JVM memory areas like different sections of a library where books (objects), bookmarks (PC Register), and study desks (stack frames) have their designated places.

🔧 Technical Explanation

Heap: Stores all objects and arrays created during runtime.
Stack: Stores frames for method invocations and local variables.
Method Area: Stores class-level data such as bytecode, constants, static variables.
Program Counter (PC) Register: Keeps track of JVM instruction being executed.
Native Method Stack: Supports native code execution via JNI.

🎯 Use Cases

✅ Proper memory organization and management in Java programs.
✅ Facilitates multi-threading with separate stacks.
✅ Supports JVM features like garbage collection and dynamic loading.

💻 Example: Inspecting JVM Memory Info


public class MemoryInfo {
    public static void main(String[] args) {
        Runtime runtime = Runtime.getRuntime();

        System.out.println("Heap Size: " + runtime.totalMemory());
        System.out.println("Max Heap Size: " + runtime.maxMemory());
        System.out.println("Free Heap Size: " + runtime.freeMemory());
    }
}

❓ Interview Q&A

Q1: What is the Heap area in JVM?
A: Stores objects and arrays during runtime.

Q2: What does the Stack area hold?
A: Method call frames and local variables.

Q3: What is stored in the Method Area?
A: Class metadata, bytecode, static variables.

Q4: What is the role of PC Register?
A: Tracks the current JVM instruction.

Q5: What is the Native Method Stack?
A: Supports native code execution.

Q6: Can JVM support multi-threading memory management?
A: Yes, with separate stacks.

Q7: Is Heap memory shared across threads?
A: Yes.

Q8: How to get JVM memory usage info?
A: Using Runtime API.

Q9: What is the significance of memory area division?
A: Efficient resource and execution management.

Q10: Can JVM dynamically load classes?
A: Yes, via Method Area and class loaders.

📝 MCQs

Q1. What is stored in JVM Heap?

Local variables
Objects and arrays
Bytecode
Program counter

Q2. What does JVM Stack store?

Objects
Method call frames and local variables
Static data
Native code

Q3. What is the Method Area?

Heap memory
Stack frames
Stores class metadata and static variables
Native stack

Q4. What does the PC Register do?

Stores variables
Tracks JVM instruction
Manages threads
Handles exceptions

Q5. What is the Native Method Stack for?

JVM code execution
Native code execution
Garbage collection
Class loading

Q6. Does each thread have its own Stack?

Yes
No
Sometimes
Never

Q7. Is Heap memory shared?

No
Yes
Sometimes
Never

Q8. How to get JVM memory info?

Manually
Using Runtime API
Through logs
None

Q9. Why is memory area division important?

For performance
For debugging
Efficient execution
For testing

Q10. Can JVM load classes dynamically?

Yes
No
Sometimes
Never

💡 Bonus Insight

Understanding JVM memory areas is vital for Java performance tuning and troubleshooting.

📄 PDF Download

Need a handy summary for your notes? Download this topic as a PDF!

📄 PDF Download Coming Soon