java.util.Observable.hasChanged()%uA0方法返回该对象是否已经改变，如是改变则返回true，否则返回false。
声明
以下是java.util.Observable.hasChanged()方法的声明
public boolean hasChanged()
参数
NA返回值
如果对象(由最近一次调用setChanged方法)改变了这个方法返回true，否则返回false。
异常
NA例子
下面的示例演示java.util.Observable.hasChanged()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)) { watchedValue = value // mark as value changed setChanged() } } } 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") } public void update(Observable obj, Object arg) { System.out.println("Update called") } }
让我们来编译和运行上面的程序，这将产生以下结果：
setValue method called... Value changed