Java Listeners

Java listeners

Created By: chatGPT

Listeners in Java are a powerful way to define how an application responds to events, such as user interactions or system changes. They follow the observer design pattern. When an event occurs, a listener interface defines what methods the program should call in response. Here’s a brief overview:

First, we need to create an interface for the listener. This interface should declare methods that will handle the events we are interested in.

public interface MyEventListener {
    void onEventOccurred(String event);
}

Next, we create a class that generates the events and manages the listeners. This class will allow others to register and unregister their listeners.

import java.util.ArrayList;
import java.util.List;

public class EventSource {
    private final List<MyEventListener> listeners = new ArrayList<>();

    public void addListener(MyEventListener listener) {
        listeners.add(listener);
    }

    public void removeListener(MyEventListener listener) {
        listeners.remove(listener);
    }

    public void triggerEvent(String event) {
        for (MyEventListener listener : listeners) {
            listener.onEventOccurred(event);
        }
    }
}

Now let's create a class that implements the listener interface. This class will provide the specific actions that should occur when the event is triggered.

public class MyListener implements MyEventListener {
    @Override
    public void onEventOccurred(String event) {
        System.out.println("Event received: " + event);
    }
}

Finally, we can test the listener mechanism by creating an instance of the event source, registering a listener, and triggering an event.

public class Main {
    public static void main(String[] args) {
        EventSource eventSource = new EventSource();
        MyListener myListener = new MyListener();

        eventSource.addListener(myListener);
        eventSource.triggerEvent("Hello, Listeners!");
    }
}