Java.util.Observable.hasChanged() 方法

描述

如果此对象已更改，则 java.util.Observable.hasChanged() 方法返回。

声明

以下是 java.util.Observable.hasChanged() 方法的声明

public boolean hasChanged()

参数

NA

返回值

如果对象已更改（通过最近调用 setChanged 方法），此方法返回 true，否则返回 false。

异常

NA

示例

下面的例子展示了 java.util.Observable.hasChanged() 方法的使用。

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 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");
   }
}

让我们编译并运行上面的程序，这将产生以下结果 −

setValue method called...
Value changed