DualListener.java Source code

Introduction

Here is the source code for DualListener.java

Source

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.event.EventListenerList;

class DualListener implements ActionListener, ChangeListener {
    public void actionPerformed(ActionEvent e) {
        System.out.println("dual: Action " + e);
    }

    public void stateChanged(ChangeEvent e) {
        System.out.println("dual: Change " + e);
    }
}

public class Main {
    public Main() {
        MyObject pair = new MyObject("This is 'a'", "This is 'b'");

        ActionListener al = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.out.println("al: Action " + e);
            }
        };

        DualListener dual = new DualListener();
        pair.addActionListener(al);
        pair.addChangeListener(dual);
        pair.setA("new A");
        pair.setB("new B");
        pair.addActionListener(dual);
        pair.setA("another A");
        pair.removeActionListener(dual);
        pair.setB("another B");
        pair.setA("final A");
    }

    public static void main(String arg[]) {
        new Main();
    }
}

class MyObject {
    Object a = null, b = null;
    EventListenerList events = new EventListenerList();
    ActionEvent actionEvent;
    ChangeEvent changeEvent;

    public MyObject(Object a1, Object b1) {
        a = a1;
        b = b1;
    }

    public void addActionListener(ActionListener listener) {
        events.add(ActionListener.class, listener);
    }

    public void removeActionListener(ActionListener listener) {
        events.remove(ActionListener.class, listener);
    }

    public void addChangeListener(ChangeListener listener) {
        events.add(ChangeListener.class, listener);
    }

    public void removeChangeListener(ChangeListener listener) {
        events.remove(ChangeListener.class, listener);
    }

    public void setA(Object newA) {
        a = newA;
        fireAChanged();
    }

    public void setB(Object newB) {
        b = newB;
        fireBChanged();
    }

    protected void fireAChanged() {
        Object[] listeners = events.getListenerList();
        for (int i = listeners.length - 2; i >= 0; i -= 2) {
            if (listeners[i] == ActionListener.class) {
                if (actionEvent == null) {
                    actionEvent = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, "a");
                }
                ((ActionListener) listeners[i + 1]).actionPerformed(actionEvent);
            }
        }
    }

    protected void fireBChanged() {
        Object[] listeners = events.getListenerList();
        for (int i = listeners.length - 2; i >= 0; i -= 2) {
            if (listeners[i] == ChangeListener.class) {
                if (changeEvent == null) {
                    changeEvent = new ChangeEvent(this);
                }
                ((ChangeListener) listeners[i + 1]).stateChanged(changeEvent);
            }
        }
    }
}