An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event.

An event adapter provides a default implementation of an event-listener interface.

In Java, event-listener interfaces and event-adapter classes are related to handling events in graphical user interface (GUI) programming. Here’s the explanation:

Event-Listener Interface:
- An event-listener interface in Java defines the methods that must be implemented by any class that wants to handle a specific type of event.
- These interfaces typically have methods like actionPerformed(), mouseClicked(), keyPressed(), etc., depending on the type of events they are designed to handle.
- Developers need to implement these interfaces in their classes to provide the actual behavior when the corresponding event occurs.
Event-Adapter Class:
- An event-adapter class is a convenience class that provides default implementations for all the methods of an event-listener interface.
- These adapter classes are useful when a developer is only interested in handling a specific type of event and doesn’t want to provide empty implementations for all methods of the corresponding event-listener interface.
- Adapter classes are designed to be subclassed, and the developer can override only the methods relevant to their requirements.

Relationship:

The relationship between an event-listener interface and an event-adapter class is one of specialization.
An event-adapter class implements the event-listener interface and provides default (often empty) implementations for all of its methods.
Developers can then choose to extend the adapter class and override only the methods they are interested in, making the code cleaner and more readable.

Here’s a simple example using the MouseListener interface and its corresponding adapter class MouseAdapter:

java

import java.awt.event.MouseAdapter;

import java.awt.event.MouseEvent;

public class MyMouseListener extends MouseAdapter { @Override public void mouseClicked(MouseEvent e) { // Override only the methods you need System.out.println("Mouse Clicked at: (" + e.getX() + ", " + e.getY() + ")"); } }

In this example, MyMouseListener extends MouseAdapter and only overrides the mouseClicked() method, leaving the other methods with default empty implementations. This allows for cleaner code when you’re only interested in handling mouse clicks.