Java.util.Observable.notifyObservers() 方法

描述

java.util.Observable.notifyObservers() 方法在对象发生变化时通知它的所有观察者。 此方法稍后会调用 clearChanged 方法来指示此对象不再更改。 该方法等价于 notifyObservers(null)。

声明

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

public void notifyObservers()

参数

NA

返回值

NA

异常

NA

示例

下面的例子展示了 java.util.Observable.notifyObservers() 方法的使用。

package com.tutorialspoint;

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)) {
         System.out.println("Value changed to new value: "+value);
         watchedValue = value;

         // mark as value changed
         setChanged();
         // trigger notification
         notifyObservers();
      }
   }
}
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
      watched.setValue("New Value");
   }
      
   public void update(Observable obj, Object arg) {
      System.out.println("Update called");
   }
}

让我们编译并运行上面的程序，这将产生以下结果 −

Value changed to new value: New Value
Update called