The specification for java.awt.Container.addImpl method says:
"Note that if the component already exists in this container or a child of this container, it is removed from that container before being added to this container."

However it is not clear what should be done if the component is added either to child of child of this container or to another container. In fact Sun JDK 5.0 RI is removing the component if it is added to another Container. You can reproduce it by following test program:
===
import java.awt.*;

public class Test extends Frame {
    public class Pane extends Panel {
        public void addImpl
                (Component comp, Object constraints, int index) {
            super.addImpl(comp, constraints, index);
        }
    }

    public Test() throws HeadlessException {
        Button btn = new Button("OK");

        Pane left = new Pane();
        left.setBackground(Color.green);
        left.addImpl(btn, null, -1);

        Pane right = new Pane();
        right.addImpl(btn, null, -1);

        Pane pane = new Pane();
        pane.setLayout(new BorderLayout());

        addImpl(left, BorderLayout.WEST, -1);
    }

    public static void main(String[] args) {
        Frame frame = new Test();

        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}
===
If you run the program above you can see a Frame without a button on the left.
But if you comment out the string "right.addImpl(btn, null, -1);" you will be able to see the disappeared button. Such behavior is not specified in the spec for java.awt.Container.addImpl and looks like a side effect.

I suppose it either should be specified in the javadoc spec or such behavior should be fixed.

###@###.### 2005-04-05 09:27:27 GMT