Java.util.Observable.clearChanged() Java.util.Observable.addObserver() Java.util.Observable.countObservers() 描述 该java.util.Observable.clearChanged()方法指示对象不再改变,或者说,它已通知其所有最近改变其观察员。notifyObservers方法自动调用此方法。 声明 以下是java.util.Observable.clearChanged()方法的声明 protected void clearChanged() 参数 NA 返回值 NA 异常 NA 实例 以下示例显示了java.util.Observable.clearChanged()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)) { watchedValue = value; // mark as value changed setChanged(); } } public void resetValue() { // reset value changed flag clearChanged(); } } 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"); // trigger reset System.out.println("resetValue method called..."); watched.resetValue(); // 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"); } } 让我们编译并运行上面的程序,这将产生以下结果 setValue method called... Value changed resetValue method called... Value not changed Java.util.Observable.addObserver() Java.util.Observable.countObservers()