The constrained property change is fired when a bean's value is about to change. When aVetoableChangeListener 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.

package org.kodejava.example.bean;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);        }    }}