Java.util.Observable.addObserver（）

描述

所述java.util.addObserver（Observer o）方法将指定观察者Ò到设定的观察员此对象，观察者是不一样的一些观察者已经在集合。

声明

以下是Java.util.Observable.addObserver（）方法的声明

public void addObserver(Observer o)

参数

o - 要添加的观察者。

返回值

NA

异常

NullPointerException - 如果指定的观察者为null。

实例

以下示例显示了java.util.Observable.addObserver（Observer）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
         notifyObservers(value);
      }
   }
}

public class ObservableDemo implements Observer {
   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();

      // trigger value change
      watched.setValue("New Value");

      // add observer to the watched object
      watched.addObserver(watcher);

      // trigger value change
      watched.setValue("Latest Value");
   }

   public void update(Observable obj, Object arg) {
      System.out.println("Update called with Arguments: "+arg);
   }
}

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
Value changed to new value: Latest Value
Update called with Arguments: Latest Value