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java.util
Class Observable

java.lang.Object
  extended by java.util.Observable
See Also:
Top Examples, Source Code, notifyObservers(), notifyObservers(java.lang.Object), Observer, Observer.update(java.util.Observable java.lang.Object)
public void addObserver(Observer o)
See Also:
NullPointerException
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[1835]Using Observable Class and Observer Interface
By anuragmishra1005 { at } yahoo { dot } com on 2006/10/26 06:24:02  Rate
There are two java programs here one is observerSubject.java and another  
 is observerClient1.java. 
  
  
 observerSubject 
  This class extends the Observable class and gets all the property of Observable class. 
  This class then creates an instance if "observerClient1" and adds this as an Observer. 
  In the program the loop is from 0 to 5 and for even value of i, the message of Object 
  "observerSubject" gets changed and its notified to the "observerClient1". 
  To notify the change to the "observerClient1" this class will call the setChanged (  )  method 
  which denotes the Object which is being observed is changed and also it uses the method 
   notifyObservers ( Object arg )   to pass the changed object to the "observerClient1". 
  
  
 observerClient1 
  This class implements the Observer interface and it must provide implementation for method 
  public void update ( Observable o, Object arg )  {  }  and the control comes here when the notification is  
  given by the observerSubject and we can call another methods from here or implement the functionality 
  which we want to do the change of the Object which this class was Observing. 
  
  
  
 /********** observerClient1.java ---STARTS -------- ***********/ 
 import java.util.Observable; 
 import java.util.Observer; 
  
  
 public class observerClient1 implements Observer {  
  
  
   public void update ( Observable o, Object arg )   {  
     observerSubject obsSubjectChanged =  ( observerSubject ) arg; 
     checkForChange ( obsSubjectChanged.getMessage (  )  ) ; 
     //System.out.println ( "The update method is called in observerClient1:::"+obsSubjectChanged.getMessage (  )  ) ; 
    }  
  
  
   public void checkForChange ( String changedMessage )  {  
     System.out.println ( "The changed message is::"+changedMessage ) ;     
    }  
  }   
 /********** observerClient1.java ---ENDS -------- ***********/ 
  
  
  
 /********** observerSubject.java ---STARTS -------- ***********/ 
 import java.util.Observable; 
  
  
 public class observerSubject extends Observable {  
    
   private String message="Hello";//This is the observerSubject property which will be changed. 
    
   public static void main ( String [  ]  args )   {  
     observerSubject obsSubject = new observerSubject (  ) ; 
     observerClient1 obzClient1 = new observerClient1 (  ) ; 
     obsSubject.addObserver ( obzClient1 ) ; 
     for  ( int i = 0; i  <  5; i++ )   {  
       if ( i%2 == 0 )  { //print only when i is even i.e 0,2,4.. 
         obsSubject.message = "hello222--"+i; 
         obsSubject.setChanged (  ) ; 
         obsSubject.notifyObservers ( obsSubject ) ; 
        }        
      }  
    }  
   //these are getter methods to get value in client class. 
   public String getMessage (  )   {  
     return message; 
    }  
   public void setMessage ( String message )   {  
     this.message = message; 
    }  
  }  
  
  
  
 /********** observerSubject.java ---ENDS-------- ***********/ 
  
  
 
protected void clearChanged()
See Also:
notifyObservers(java.lang.Object), notifyObservers()
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public int countObservers()
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public void deleteObserver(Observer o)
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public void deleteObservers()
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public boolean hasChanged()
See Also:
setChanged(), clearChanged()
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public void notifyObservers()
See Also:
Observer.update(java.util.Observable, java.lang.Object), hasChanged(), clearChanged()
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public void notifyObservers(Object arg)
See Also:
Observer.update(java.util.Observable, java.lang.Object), hasChanged(), clearChanged()
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public Observable()
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protected void setChanged()
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