Java Reference
In-Depth Information
Setting Up Components
When you make a class an event listener, you have set up a specific type of event to be
heard by that class. However, the event won't actually be heard unless you follow up
with a second step: A matching listener must be added to the component. That listener
generates the events when the component is used.
After a component is created, you can call one of the following methods on the compo-
nent to associate a listener with it:
addActionListener() JButton , JCheckBox , JComboBox , JTextField ,
JRadioButton , and JMenuItem components
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addFocusListener() —All Swing components
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addItemListener() JButton , JCheckBox , JComboBox , and JRadioButton compo-
nents
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addKeyListener() —All Swing components
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addMouseListener() —All Swing components
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addMouseMotionListener() —All Swing components
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addTextListener() JTextField and JTextArea components
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addWindowListener() JWindow and JFrame components
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CAUTION
Modifying a component after adding it to a container is an easy
mistake to make in a Java program. You must add listeners to a
component and handle any other configuration before the compo-
nent is added to any containers; otherwise, these settings are dis-
regarded when the program is run.
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The following example creates a JButton object and associates an action event listener
with it:
JButton zap = new JButton(“Zap”);
zap.addActionListener(this);
All the listener adding methods take one argument: the object that is listening for events
of that kind. Using this indicates that the current class is the event listener. You could
specify a different object, as long as its class implements the right listener interface.
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