CODEWITHSUNDEEP
javaoopgarbage-collection
Eliezer
Eliezer

Reputation: 7347

Java Does Nested Class Instance Prevent GC of Outer Class

Assume Outer is instantiated somewhere, and after a while there are no references to it. Does the implicit reference in inner to the Outer instance prevent GC from running, or does the is it a "special" reference?

public class Outer {
    private class Inner extends Something {}

    private Inner inner = new Inner();
}

Upvotes: 1

Views: 221

Answers (1)

jdphenix
jdphenix

Reputation: 15425

If the instance of Outer is not reachable from a GC root, the reference to an Inner instance in your example code will not stop the garbage collector from freeing the memory the Outer used.

Consider this diagram: 

Stack of main thread           public static void main(String[] args) {
         |                       Outer outer = new Outer();
         v                     
       Outer<--\
         |\    |
         v \---/
       Inner 

Stack of main thread               outer = new Outer();
         |
         v          
       Outer<--\
         |\ new|
         v \---/
       Inner 

       Outer<--\                   // a reference to the Outer from the Inner
         |\ old|                   // doesn't change the fact that the Outer
         v \---/                   // can't be reached from a GC root.
       Inner                       // Thus the old Outer is eligible for collection (dead)

Upvotes: 3

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