Java Reference
In-Depth Information
Centralized receipt of events
In order to make our ImageViewer object be the single listener to all events from the menu, we
have to do three things:
We must declare in the class header that it implements the ActionListener interface.
We have to implement a method with the signature
public void actionPerformed(ActionEvent e)
This is the only method declared in the ActionListener interface.
We must call the addActionListener method of the menu item to register the
ImageViewer object as a listener.
Numbers 1 and 2—implementing the interface and defining its method—ensure that our object
is a subtype of ActionListener . Number 3 then registers our own object as a listener for the
menu items. Code 11.3 shows the source code for this in context.
Code 11.3
Adding an action
listener to a menu item
public class ImageViewer
implements ActionListener
// Fields and constructor omitted.
public void actionPerformed(ActionEvent event)
System.out.println( "Menu item: " + event.getActionCommand());
* Create the Swing frame and its content.
private void makeFrame()
frame = new JFrame( "ImageViewer" );
// Other GUI building code omitted.
* Create the main frame's menu bar.
* @param frame The frame the menu bar should be added to.
private void makeMenuBar(JFrame frame)
JMenuBar menubar = new JMenuBar();
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