java.util.addObserver(Observer o)%uA0方法将指定observer%uA0o%uA0到该observers为此对象，如果observer 不同于已经在集合中一些observer。
声明
以下是Java.util.Observable.addObserver()方法的声明
public void addObserver(Observer o)
参数
-
o%uA0-- 要添加的observer
返回值
NA
异常
-
NullPointerException%uA0-- 如果指定的%uA0observer 为%uA0null.
例子
下面的示例演示java.util.Observable.addObserver(Observer)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)) { 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) } }
让我们来编译和运行上面的程序，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