Does reassigning the object reference variable kill the old object?

Question

If I have a class, CatFrame, that extends JFrame then I set myCat = new CatFrame(); then later I do myCat = new CatFrame(false);. Is the old CatFrame eligible for garbage collection?

public class CatFrame extends JFrame{
    public CatFrame(){
         this.setVisible(false);
    }

public CatFrame(boolean b){
         this.setVisible(false);
    }
}

see [Remove Top-Level Container on Runtime](http://stackoverflow.com/questions/6309407/remove-top-level-container-on-runtime) — mKorbel, Jun 28 '16 at 19:30

score 8 · Accepted Answer · answered Jun 28 '16 at 18:18

You need to be careful with Swing components that extend Window, like JFrame and JDialog, as they have peer components that will not be garbage collected. To gc a Window properly, use Window.dispose();

But otherwise, once an object on the heap is not reachable from any active thread, that object is eligible for garbage collection

Infamous911 · Answer 2 · 2016-06-28T18:23:39.707

1

Yes. You are replacing "old" CatFrame with the "new" one, thus allowing the "old" CatFrame to be collected by the garbage collector because it is no longer accessible in any way by your program (if that was the only reference).

EDIT:

JFrames and other such objects are little tricky though. See ControlAltDel's answer.

edited Jun 28 '16 at 18:23

answered Jun 28 '16 at 18:14

Infamous911

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Unless the reference to the old object has been preserved prior to reassignment. – PM 77-1 Jun 28 '16 at 18:15
2

Or that object is a Window that has been shown. See Window.dispose() – ControlAltDel Jun 28 '16 at 18:18
Wrong, frames need to be disposed, UI stack can retain some objects, especially frames. – Jean-Baptiste Yunès Jun 28 '16 at 18:20

Does reassigning the object reference variable kill the old object?

2 Answers2