| Java Listener & Event Handlers |
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Java applets interactive! We can use inheritance and abstract classes to further the event handling process. This is where the EventObject, which is the parent to the AWTEvent comes into play. Below are some user actions and the event types associated with them:
|
User Action
|
Event Type
|
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Click a Button
|
ActionEvent
|
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Click a Component
|
MouseEvent
|
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Click an item in a Choice
|
ItemEvent
|
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Click an item in a Checkbox
|
ItemEvent
|
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Change text in a TextField
|
TextEvent
|
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Open a window
|
WindowEvent
|
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Iconify a window
|
WindowEvent
|
|
Type a key
|
KeyEvent
|
As you may have guessed, every
xxxEvent requires an xxxListener, which has the return type void.
Remembering that interfaces contain abstract methods, which are empty methods,
in order to implement a listener, you must provide your own methods for all the
methods that are part of the interface. Although you can leave the methods
empty in your implementation. The following table shows the events, their
listeners, and their handlers:
|
Event
|
Listener
|
Handlers
|
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ActionEvent
|
ActionListener
|
actionPerformed(ActionEvent)
|
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ItemEvent
|
ItemListener
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itemStateChanged(ItemEvent)
|
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TextEvent
|
TextListener
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textValueChanged(TextEvent)
|
|
AdjustmentEvent
|
AdjustmentListener
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adjustmentValueChanged(AdjustmentEvent)
|
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ContainerEvent
|
ContainerListener
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componentAdded(ContainerEvent)
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|
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componentRemoved(ContainerEvent)
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ComponentEvent
|
ComponentListener
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componentMoved(ComponentEvent)
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componentHidden(ComponentEvent)
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componentResized(ComponentEvent)
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|
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componentShown(ComponentEvent)
|
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FocusEvent
|
FocusListener
|
focusGained(FocusEvent)
|
|
|
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focusLost(FocusEvent)
|
|
MouseEvent
|
MouseListener
|
mousePressed(MouseEvent)
|
|
|
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mouseReleased(MouseEvent)
|
|
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mouseEntered(MouseEvent)
|
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mouseExited(MouseEvent)
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mouseClicked(MouseEvent)
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MouseMotionListener
|
mouseDragged(MouseEvent)
|
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mouseMoved(MouseEvent)
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KeyEvent
|
KeyListener
|
keyPressed(KeyEvent)
|
|
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keyTyped(KeyEvent)
|
|
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keyReleased(KeyEvent)
|
|
WindowEvent
|
ComponentListener
|
windowMoved(WindowEvent)
|
|
|
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windowActivated(WindowEvent)
|
|
|
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windowClosing(WindowEvent)
|
|
|
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windowClosed(WindowEvent)
|
|
|
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windowDeiconified(WindowEvent)
|
|
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windowIconified(WindowEvent)
|
|
|
|
windowOpened(WindowEvent)
|
| 
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