Java Java.util.Observable.notifyObservers()用法及代碼示例

描述

這個java.util.Observable.notifyObservers(Object arg)如果此對象已更改，則方法通知其所有觀察者，然後調用 clearChanged 方法以指示此對象已不再更改。

聲明

以下是聲明java.util.Observable.notifyObservers()方法

public void notifyObservers(Object arg)

參數

arg─ 任何物體。

返回值

NA

異常

NA

示例

下麵的例子展示了 java.util.Observable.notifyObservers(Object) 方法的用法。

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 with arguments
         notifyObservers(value);
      }
   }
}
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(name+" called with Arguments:"+arg);
   }
}

讓我們編譯並運行上麵的程序，這將產生以下結果——

Value changed to new value:New Value
Watcher called with Arguments:New Value