JAVA-MANI.BLOGSPOT.COM

The constrained property change is fired when a bean's value is about to change. When a VetoableChangeListener veto the value change the bean's value will be rolled-back to the previous value. In this example we have a constrained property called interest.


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

public class VetoBean {
private double interest;

private VetoableChangeSupport vcs = new VetoableChangeSupport(this);

public VetoBean() {
vcs.addVetoableChangeListener(new VetoChangeListener());
}

public double getInterest() {
return interest;
}

public void setInterest(double interest) {
try {
vcs.fireVetoableChange("interest", new Double(this.interest), new Double(interest));

this.interest = interest;
} catch (PropertyVetoException e) {
e.printStackTrace();
}
}

public static void main(String[] args) {
VetoBean bean = new VetoBean();
bean.setInterest(10.99);
bean.setInterest(15.99);

//
// PropertyVetoException will be thrown beacuse the interest value
// should not exceed 20.00.
//
bean.setInterest(20.99);
}
}

package org.kodejava.example.bean;

import java.beans.VetoableChangeListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyVetoException;

public class VetoChangeListener implements VetoableChangeListener {
/**
* This method gets called when a constrained property is changed.
*
* @param evt a PropertyChangeEvent object describing the
* event source and the property that has changed.
* @throws java.beans.PropertyVetoException
* if the recipient wishes the property
* change to be rolled back.
*/
public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {
String eventName = evt.getPropertyName();
if (eventName.equalsIgnoreCase("interest")) {
double interest = ((Double) evt.getNewValue()).doubleValue();
if (interest > 20.00) {
throw new PropertyVetoException("Interest must be below 20.00", evt);
}
System.out.println("Interest applied = " + interest);
}
}
}