How do I listen for a constrained property change?

By Wayan in Beans 0 Comment

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.

package org.kodejava.bean;

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

public class VetoBean {
    private double interest;

    private final VetoableChangeSupport vcs = new VetoableChangeSupport(this);

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

    public void setInterest(double interest) {
        try {
            vcs.fireVetoableChange("interest", this.interest, 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 because the interest value
        // should not exceed 20.00.
        bean.setInterest(20.99);
    }
}

package org.kodejava.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();
            if (interest > 20.00) {
                throw new PropertyVetoException("Interest must be below 20.00", evt);
            }
            System.out.println("Interest applied = " + interest);
        }
    }
}
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