Graphical User Interfaces - Building Java Programs: A Back to Basics Approach - page 871

The code places the buffered image onto a label as its icon, then stores the
buffered image into a panel that is placed inside the frame. We use this intermediate
panel to ensure that the background colors are set properly.
Second Version with Events
A more sophisticated version of DrawingPanel will also act as an event listener
for mouse events, so that as the user drags the mouse over the panel, the program
will display the cursor's ( x, y ) position on a status bar at the bottom for debugging.
To achieve this, the DrawingPanel can be modified to act as a mouse listener and
attach itself to listen to its central panel. Whenever the mouse moves, the mouse
listener will receive the event and will update the status bar text to show the mouse
position.
To implement these capabilities, we'll begin by changing our class header to the
following header:
public class DrawingPanel extends MouseInputAdapter {
We'll then add a new field called statusBar , of type JLabel , to the program
and place it in the south region of the frame. Initially the status bar's text will be
empty, but if the mouse moves, its listener will change the text to reflect the cur-
sor's position. The following code implements the mouse listener's mouseMoved
method:
// draws status bar text when mouse moves
public void mouseMoved(MouseEvent e) {
statusBar.setText("(" + e.getX() + ", " + e.getY() + ")");
}
We'll also add the following code to the constructor to attach the DrawingPanel
as a listener to its inner panel:
// attach listener to observe mouse movement
panel.addMouseListener(this);
panel.addMouseMotionListener(this);
There's another kind of event that we should handle in the DrawingPanel .
When the client code using DrawingPanel takes a long time (such as when it
uses console input to guide what shapes will be drawn), we may need to repaint
the DrawingPanel periodically to reflect any new shapes that the client has
drawn. To keep things simple, we don't want to force the client to call repaint
itself.
To force the DrawingPanel to refresh at a given interval, we'll use a Timer to
periodically call repaint . Since a Timer requires an action listener as a parameter,