The following source code demonstrates the problem.

When the button "Add" is pressed the TestPanel 'p' is first removed from the container then a new TestPanel 'p' is created and added to the Container. The problem being demonstarted is the the original TestPanel is never gc()'d because the GridBagLayout continues to hold a reference to it. When I invoke remove, I
expect that to be the end of the relationship between the container and the
Component.


import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class TestApplet extends Applet implements ActionListener {
        Button add = new Button("Add");
        TestPanel p = new TestPanel();

    public void init() {
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();

        gbc.gridx = 0;
        gbc.gridy = 0;
        add(add, gbc);
        add.addActionListener(this);

        gbc.gridy = 1;
        add(p, gbc);
    }

    public void actionPerformed(ActionEvent actionEvent) {
        remove(p);

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = 1;

        p = new TestPanel();
        add(p, gbc);

        System.out.println("Starting gc()");
        System.gc();
        System.runFinalization();
        System.out.println("Ending gc()");
    }
}

class TestPanel extends Panel {
    public void finalize() throws Throwable {
        System.out.println("TestPanel.finalize()");
    }
}

[This problem shows up in win_95, win_nt_4.0 and Solaris]

***********************
Steve Fleming, 5/11/98

This problem also was found by WebLogic.
The severity is probably more than 5, because this bug leads to memory
leaks in certain applications since GC will not work as expected.
Console type applications with continuously updated displays are
especially impacted by the failure to GC.

Given the increased severity and the ease of fix, it would be nice
to see this bug fixed in 1.2.
See below:
> The bug in GridBagLayout is that removing an object leaves a ref to
> the object in the comptable so it never gets gc'd.
>
> Here's our fix, in a subclass of GridBagLayout:
>
> /**
> * Fixes a bug in GridBagLayout where constraints are left in the comptable,
> * This bug prevents garbage collection of any components removed from the
layout.
> */
> public void removeLayoutComponent(Component comp) {
> comptable.remove(comp);
> }
>
> Gary Aitken ###@###.###