Java Observable clearChanged() 方法

描述

Java Observable clearChanged(Observer o) 方法表示该对象不再发生变化，或者它已经通知了所有观察者其最近的变化。此方法由notifyObservers方法自动调用。

声明

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

protected void clearChanged()

参数

无

返回值

无

异常

无

为字符串值更改的观察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我们通过扩展 Observable 类并覆盖其 resetValue() 方法（调用 clearChanged() 方法）创建了一个 ObservedObject 类。在主类中，我们使用 addObserver() 方法添加了观察者，并在输出中打印了 ObservedObject 值发生的更新。

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();
      }
   }
	  
   public void resetValue() {
      // reset value changed flag
       clearChanged();
   }   
}

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("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 with Arguments: "+arg);
   }
}

输出

让我们编译并运行上述程序，这将产生以下结果：

setValue method called...
Value changed
resetValue method called...
Value not changed

为整数值更改的观察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我们通过扩展 Observable 类并覆盖其 resetValue() 方法（调用 clearChanged() 方法）创建了一个 ObservedObject 类。在主类中，我们使用 addObserver() 方法添加了观察者，并在输出中打印了 ObservedObject 值发生的更新。

package com.tutorialspoint;

import java.util.Observable;
import java.util.Observer;

class ObservedObject extends Observable {
   private Integer watchedValue;
   
   public ObservedObject(Integer value) {
      watchedValue = value;
   }
      
   public void setValue(Integer 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();
      }
   }  
   public void resetValue() {
      // reset value changed flag
      clearChanged();
   }
}

public class ObservableDemo implements Observer {
   public static void main(String[] args) {
      
      // create watched and watcher objects
      ObservedObject watched = new ObservedObject(1);
      
      // 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(2);
      
      // 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 with Arguments: "+arg);
   }
}

输出

让我们编译并运行上述程序，这将产生以下结果：

setValue method called...
Value changed
resetValue method called...
Value not changed

为对象值更改的观察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我们通过扩展 Observable 类并覆盖其 resetValue() 方法（调用 clearChanged() 方法）创建了一个 ObservedObject 类。在主类中，我们使用 addObserver() 方法添加了观察者，并在输出中打印了 ObservedObject 值发生的更新。

package com.tutorialspoint;

import java.util.Observable;
import java.util.Observer;

class ObservedObject extends Observable {
   private Student watchedValue;
   
   public ObservedObject(Student value) {
      watchedValue = value;
   }
      
   public void setValue(Student 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();
      }
   }  
	
   public void resetValue() {
      // reset value changed flag
      clearChanged();
   }
}

public class ObservableDemo implements Observer {
   public static void main(String[] args) {
      
      // create watched and watcher objects
      ObservedObject watched = new ObservedObject(new Student(1, "Julie"));
      
      // 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 Student(2, "Robert"));
      
      // 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 with Arguments: "+arg);
   }
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

输出

让我们编译并运行上述程序，这将产生以下结果：

setValue method called...
Value changed
resetValue method called...
Value not changed