Listener Model The listener model is a design pattern that allows an object to react to events from other objects. When an event occurs on one object, it tr...
Listener Model
The listener model is a design pattern that allows an object to react to events from other objects. When an event occurs on one object, it triggers a method on another object that is registered as a listener. This allows multiple objects to be notified of the same event, and each object can handle the event in its own way.
How it works:
Event source: An object that generates the event, such as a button or a text field.
Listener interface: An interface that defines the methods that will be called when the event occurs.
Listener objects: Objects that implement the listener interface and subscribe to the event source.
Event: When the event source fires an event, it sends an event object to all registered listeners.
Method invocation: When an event occurs, the event object is dispatched to the corresponding listener object.
Listener execution: The listener object calls the handleEvent method, which is defined in the listener interface.
Event propagation: The event is passed down the listener hierarchy, until it is handled by the most specific listener object.
Example:
java
// Define the listener interface
interface ActionListener {
public void actionPerformed(ActionEvent e);
}
// Implement the listener interface in a concrete class
class ButtonListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
// Button clicked event handling logic
}
}
// Create an event source
Button button = new Button("Click me");
// Register a listener for the action event
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
// Event handled by the button listener
}
});
// Add the button to a panel
panel.add(button);
In this example, the Button object generates an ActionEvent when it is clicked. The ActionListener is a class that implements the ActionListener interface. When the event is fired, the actionPerformed method of the listener object is called. This method can then execute any necessary actions, such as displaying a message or updating a UI component