Implementing a Constrained Property: fires a PropertyChangeEvent whenever its value is about to be changed. : JavaBeans « Development « Java Tutorial

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import java.beans.PropertyVetoException;
import java.beans.VetoableChangeListener;
import java.beans.VetoableChangeSupport;

public class MyBean {
  VetoableChangeSupport vceListeners = new VetoableChangeSupport(this);

  int myProperty;

  public int getMyProperty() {
    return myProperty;
  }

  public void setMyProperty(int newValue) throws PropertyVetoException {
    try {
      vceListeners.fireVetoableChange("myProperty", new Integer(myProperty),
          new Integer(newValue));
      myProperty = newValue;
    } catch (PropertyVetoException e) {
      throw e;
    }
  }

  public synchronized void addVetoableChangeListener(
      VetoableChangeListener listener) {
    vceListeners.addVetoableChangeListener(listener);
  }

  public synchronized void removeVetoableChangeListener(
      VetoableChangeListener listener) {
    vceListeners.removeVetoableChangeListener(listener);
  }

}