Java GC/Memory Model Questions

GC
1. What are the six reachability states in Java?
    Strongly reachable objects
    Softly reachable objects
    Weakly reachable objects
    (Weak Refer: a reference that doesn't protect the referenced object from collection)
    Resurrect-able reachable objects
    Phantomly reachable objects
    Unreachable reachable objects

    https://stackoverflow.com/questions/299659/what-is-the-difference-between-a-soft-reference-and-a-weak-reference-in-java

2. How does GC work and when do JVM perform GC


What is Eden: newly created objects will be putted here
What is survivor: objects which survived Eden GC
Why there are two survivors: Only put things to old generation if objects survives many GC

What are the major GCs:
Minor GC:  Clean eden, move Eden to survivors

Full GC:     Clean entire heap space

When to collet:
Minor  When don't have enough space to allocate new space in Eden
Major:  New candidate for Old generation is bigger than free space in Old generation

What to collect:
    Go through GC roots. Any unreachable objects will be marked as OK to collect

What happened:
    stop some threads and finalize some objects




Memory Model

We have stack and heap memories.

Stack:     
What's inside:
method (call stack) and local primitive variables. Each thread has stack space here

What gonna happen if stack is full:
StackoverFlow Error

Life Cycle:


Heap:  
What's inside:
all reference objects(literally all)

What gonna happen if stack is full:
OutOfMemoryError Error


Size of Stack >> Size of Heap