Event and Listener (Java Event Handling)

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.

Java 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 Event Handling

Following steps are required to perform event handling:

  1. Register the component with the Listener

Registration Methods

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

Button

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){}


Java Event Handling Code

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

  1. Within class
  2. Other class
  3. Anonymous class

Java event handling by implementing ActionListener

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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.

2) Java event handling by outer class

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3) Java event handling by anonymous class

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