constrainedattrbean.java

精通JBuilder2006 源代码 精通JBuilder2006 源代码

package chapter7.attribute;

import java.awt.*;
import java.beans.*;

public class ConstrainedAttrBean extends Canvas {
  private PropertyChangeSupport changes = new PropertyChangeSupport(this);
  private VetoableChangeSupport vetos = new VetoableChangeSupport(this);
  int ourPriceInCents;  //ourPriceInCents是一个Constrained属性
  public void setPriceInCents(int newPriceInCents) throws PropertyVetoException {
    int oldPriceInCents = ourPriceInCents;     // 先保存原来的属性值
    /*触发属性改变否决事件*/
    vetos.fireVetoableChange("priceInCents", new Integer(oldPriceInCents),
                             new Integer(newPriceInCents));
/*若有其他对象否决priceInCents的改变，则程序抛出例外，不再继续执行下面的两条语句，方法结束。若无其他对象否决priceInCents的改变，则在下面的代码中把ourPriceIncents赋予新值，并触发属性改变事件*/
    ourPriceInCents = newPriceInCents;
    changes.firePropertyChange("priceInCents", new Integer(oldPriceInCents),
                               new Integer(newPriceInCents));
  }
/*为PriceInCents属性预留接口，使其他对象可注册入PriceInCents否决改变监听者队列中*/
  public void addVetoableChangeListener(VetoableChangeListener l) {
    vetos.addVetoableChangeListener(l);
  }
/*为PriceInCents属性预留接口，使其他对象可从PriceInCents否决改变监听者队列中注销*/
  public void removeVetoableChangeListener(VetoableChangeListener l) {
    vetos.removeVetoableChangeListener(l);
  }
}