java.util.Observable.hasChanged() 方法返回该对象是否已经改变，如是改变则返回true，否则返回false。

声明

以下是java.util.Observable.hasChanged()方法的声明

public boolean hasChanged()

参数

NA

返回值

如果对象(由最近一次调用setChanged方法)改变了这个方法返回true，否则返回false。

异常

NA

例子

下面的示例演示java.util.Observable.hasChanged()方法的用法。

package com.yiibai;

import java.util.Observable;
import java.util.Observer;

class ObservedObject extends Observable {
   private String watchedValue;
   
   public ObservedObject(String value) {
      watchedValue = value;
   }
   
   public void setValue(String value) {
      // if value has changed notify observers
      if(!watchedValue.equals(value)) {
         watchedValue = value;
         
         // mark as value changed
         setChanged();
      }
      
   }
}
public class ObservableDemo implements Observer {
   public String name;
   public ObservableDemo(String name) {
      this.name = name;
   }
   
   public static void main(String[] args) {
      // create watched and watcher objects
      ObservedObject watched = new ObservedObject("Original Value");
      // watcher object listens to object change
      ObservableDemo watcher = new ObservableDemo("Watcher");
      // add observer to the watched object
      watched.addObserver(watcher);

      // trigger value change
      System.out.println("setValue method called...");
      watched.setValue("New Value");
      // check if value has changed
      if(watched.hasChanged())
         System.out.println("Value changed");
      else
         System.out.println("Value not changed");
   }
   
   public void update(Observable obj, Object arg) {
      System.out.println("Update called");
   }
}

让我们来编译和运行上面的程序，这将产生以下结果：

setValue method called...
Value changed