Listening for a Property Change Event: A property change event is fired when a bound property is changed. : JavaBeans « Development « Java Tutorial

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import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

public class Main {
  public static void main(String[] argv) throws Exception {
    MyBean bean = new MyBean();

    bean.addPropertyChangeListener(new MyPropertyChangeListener());
  }
}

class MyPropertyChangeListener implements PropertyChangeListener {
  public void propertyChange(PropertyChangeEvent evt) {
    Object oldValue = evt.getOldValue();

    Object newValue = evt.getNewValue();
  }
}

class MyBean {
  PropertyChangeSupport pceListeners = new PropertyChangeSupport(this);

  int myProperty;

  public int getMyProperty() {
    return myProperty;
  }

  public void setMyProperty(int newValue) {
    int oldValue = myProperty;
    myProperty = newValue;
    pceListeners.firePropertyChange("myProperty", new Integer(oldValue),
        new Integer(newValue));
  }

  public synchronized void addPropertyChangeListener(
      PropertyChangeListener listener) {
    pceListeners.addPropertyChangeListener(listener);
  }

  public synchronized void removePropertyChangeListener(
      PropertyChangeListener listener) {
    pceListeners.removePropertyChangeListener(listener);
  }

}