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.
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