Event Handling

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Changing the state of an object is known as an event. For example, click on button, dragging mouse etc. The java.awt.event package provides many event classes and Listener interfaces for event handling.

Event classes and Listener interfaces:

Event Classes Listener Interfaces
ActionEvent ActionListener
MouseEvent MouseListener and MouseMotionListener
MouseWheelEvent MouseWheelListener
KeyEvent KeyListener
ItemEvent ItemListener
TextEvent TextListener
AdjustmentEvent AdjustmentListener
WindowEvent WindowListener
ComponentEvent ComponentListener
ContainerEvent ContainerListener
FocusEvent FocusListener

Steps to perform EventHandling:

Following steps are required to perform event handling :

  1. Implement the Listener interface and overrides its methods
  2. Register the component with the Listener

For registering the component with the Listener, many classes provide the registration methods. For example:

  • Button
    • public void addActionListener(ActionListener a){}
  • MenuItem
    • public void addActionListener(ActionListener a){}
  • TextField
    • public void addActionListener(ActionListener a){}
    • public void addTextListener(TextListener a){}
  • TextArea
    • public void addTextListener(TextListener a){}
  • Checkbox
    • public void addItemListener(ItemListener a){}
  • Choice
    • public void addItemListener(ItemListener a){}
  • List
    • public void addActionListener(ActionListener a){}
    • public void addItemListener(ItemListener a){}

EventHandling Codes:

We can put the event handling code into one of the following places:

  1. Same class
  2. Other class
  3. Annonymous class

Example of event handling within class:


 

public void setBounds(int xaxis, int yaxis, int width, int height); have been used in the above example that sets the position of the component it may be button, textfield etc.

Event Handling


2) Example of event handling by Outer class:


 


 


3) Example of event handling by Annonymous class:


 

 

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