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Event
Handling
Detecting an event and carrying out the required task is known as handling the event.
Programs following this paradigm are known as event-driven
programs.
A program handling button events is demonstrated with the help of the following applet:
Listing 2.1.1 shows the source code for the above program.
In the above applet, the Button is the GUI component. Once the GUI components
are created, they need to respond to user actions. This is accomplished by adding
various types of listeners to the GUI components. One (or more) listener objects added to the
GUI components handle the events generated by the GUI component. The listener object can be
the applet itself or any other object. For now, we will focus on the applet having the role
of the listener and responding to the user actions. Depending on what type of component and
the type of the listener, the corresponding methods written within the applet handle the
user events. The table below shows some of the listeners for the corresponding GUI components.
| GUI Component | Listener | Event Handling
Method(s) |
| JButton | ActionListener | actionPerformed |
| JSlider | ChangeListener | stateChanged |
| JTextField | ActionListener | actionPerformed |
| JCheckBox | ItemListener | itemStateChanged |
| JRadioButton | ActionListener | actionPerformed |
| JMenuItem | ActionListener | actionPerformed |
| JComboBox | ActionListener | actionPerformed |
| ItemListener | itemStateChanged |
| JApplet |
MouseListener | mousePressed, mouseReleased, mouseClicked,
etc. |
| MouseMotionListener | mouseMoved, mouseDragged |
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