Java Observable clearChanged() 方法

描述

Java Observable clearChanged(Observer o) 方法表示該物件不再發生變化，或者它已經通知了所有觀察者其最近的變化。此方法由notifyObservers方法自動呼叫。

宣告

以下是Java.util.Observable.clearChanged()方法的宣告

protected void clearChanged()

引數

無

返回值

無

異常

無

為字串值更改的觀察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我們透過擴充套件 Observable 類並覆蓋其 resetValue() 方法（呼叫 clearChanged() 方法）建立了一個 ObservedObject 類。在主類中，我們使用 addObserver() 方法添加了觀察者，並在輸出中列印了 ObservedObject 值發生的更新。

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);
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

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

為整數值更改的觀察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我們透過擴充套件 Observable 類並覆蓋其 resetValue() 方法（呼叫 clearChanged() 方法）建立了一個 ObservedObject 類。在主類中，我們使用 addObserver() 方法添加了觀察者，並在輸出中列印了 ObservedObject 值發生的更新。

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);
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

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

為物件值更改的觀察者清除更改示例

以下示例演示了 java.util.Observable.clearChanged() 方法的使用。我們透過擴充套件 Observable 類並覆蓋其 resetValue() 方法（呼叫 clearChanged() 方法）建立了一個 ObservedObject 類。在主類中，我們使用 addObserver() 方法添加了觀察者，並在輸出中列印了 ObservedObject 值發生的更新。

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 + " ]";
   }
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

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