Re: why use final here

class MouseEvents {
       public static void main(String args[]) {
               final Frame mainWindow = new Frame("Main Window");
               Button btnClr = new Button("Clear");
               btnClr.addMouseListener(new MouseAdapter() {
                               public void mouseClicked(MouseEvent
me) {
                                       mainWindow.repaint();
                               }
                       } );
               mainWindow.setSize(200,200);
               mainWindow.setLayout(new FlowLayout());
               mainWindow.add(btnClr);
               mainWindow.setVisible (true);
               mainWindow.addMouseListener(new
MyMouseAdapter(mainWindow));
       }
}

class MyMouseAdapter extends MouseAdapter {
       Frame FListener;
       MyMouseAdapter(Frame FListener) {
               this.FListener = FListener;
       }
       public void mouseClicked(MouseEvent me) {

FListener.getGraphics().drawString("*",me.getX(),me.getY());
       }
}

The problem is that use of mainWindow (as used for the mouseClick
event of the btnClr) requires mainWindow to be final because *too*
much nesting. Why? Couldn't get it.