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Java觀察者模式例子
被觀察者的接口類
import java.util.Observer;
/**
* 氣溫預報(觀察者模式)
* @author Administrator
*被觀察者接口即subject目標接口氣溫
*/
public interface Temperature{
//增加觀察者
public void addObs(Observer o);
//刪除觀察者
public void deleteObs(Observer o);
//通知觀察者
public void notifyObs(int t);
}
被觀察者實現類
/**
* 具體主題被觀察者
* @author Administrator
*
*/
public class TemperatureImpl extends Observable implements Temperature {
@Override
public synchronized void addObserver(Observer o) {
super.addObserver(o);
}
@Override
public synchronized void deleteObserver(Observer o) {
super.deleteObserver(o);
}
@Override
public void notifyObservers(Object arg) {
super.setChanged();
super.notifyObservers(arg);
}
/**
* 當具體被觀察者類集成Observable時這些其實時不需要的,因為在Observable類中其實已經有定義,
* 上麵的重寫這些方法已經足夠(也可不重寫直接調用父類的方法)
* 如果采用下麵的方法就相當於自己實現觀察者模式,不用api中提供的類
* 必須加上相應的Vector obs觀察者數組用於存放觀察者列表
*/
@Override
public void addObs(Observer o) {
}
@Override
public void deleteObs(Observer o) {
}
@Override
public void notifyObs(int t) {
}
}
觀察者接口類
import java.util.Observer;
/**
* 氣溫顯示(根據氣溫的實時變化來實時顯示)
* @author Administrator
*
*/
public interface TemperatureShow extends Observer {
}
觀察者實現類
import java.util.Observable;
public class TemperatureShowImpl implements TemperatureShow {
public String tname;
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
@Override
public void update(Observable o, Object arg) {
System.out.println(tname+":"+arg);
}
}
測試類
public class TestMain{
public static double i=0;
public static void main(String[] args) {
//創建被觀察者
TemperatureImpl t = new TemperatureImpl();
//創建觀察者1
TemperatureShowImpl s = new TemperatureShowImpl();
s.setTname("高溫預報");
t.addObserver(s);
//創建觀察者2
TemperatureShowImpl s1 = new TemperatureShowImpl();
s1.setTname("低溫預報");
t.addObserver(s1);
t.notifyObservers(Math.random());
}
}
這裏附上Observable類
/*
* @(#)Observable.java 1.39 05/11/17
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util;
/**
* This class represents an observable object, or "data"
* in the model-view paradigm. It can be subclassed to represent an
* object that the application wants to have observed.
* <p>
* An observable object can have one or more observers. An observer
* may be any object that implements interface <tt>Observer</tt>. After an
* observable instance changes, an application calling the
* <code>Observable</code>'s <code>notifyObservers</code> method
* causes all of its observers to be notified of the change by a call
* to their <code>update</code> method.
* <p>
* The order in which notifications will be delivered is unspecified.
* The default implementation provided in the Observable class will
* notify Observers in the order in which they registered interest, but
* subclasses may change this order, use no guaranteed order, deliver
* notifications on separate threads, or may guarantee that their
* subclass follows this order, as they choose.
* <p>
* Note that this notification mechanism is has nothing to do with threads
* and is completely separate from the <tt>wait</tt> and <tt>notify</tt>
* mechanism of class <tt>Object</tt>.
* <p>
* When an observable object is newly created, its set of observers is
* empty. Two observers are considered the same if and only if the
* <tt>equals</tt> method returns true for them.
*
* @author Chris Warth
* @version 1.39, 11/17/05
* @see java.util.Observable#notifyObservers()
* @see java.util.Observable#notifyObservers(java.lang.Object)
* @see java.util.Observer
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
* @since JDK1.0
*/
public class Observable {
private boolean changed = false;
private Vector obs;
/** Construct an Observable with zero Observers. */
public Observable() {
obs = new Vector();
}
/**
* Adds an observer to the set of observers for this object, provided
* that it is not the same as some observer already in the set.
* The order in which notifications will be delivered to multiple
* observers is not specified. See the class comment.
*
* @param o an observer to be added.
* @throws NullPointerException if the parameter o is null.
*/
public synchronized void addObserver(Observer o) {
if (o == null)
throw new NullPointerException();
if (!obs.contains(o)) {
obs.addElement(o);
}
}
/**
* Deletes an observer from the set of observers of this object.
* Passing <CODE>null</CODE> to this method will have no effect.
* @param o the observer to be deleted.
*/
public synchronized void deleteObserver(Observer o) {
obs.removeElement(o);
}
/**
* If this object has changed, as indicated by the
* <code>hasChanged</code> method, then notify all of its observers
* and then call the <code>clearChanged</code> method to
* indicate that this object has no longer changed.
* <p>
* Each observer has its <code>update</code> method called with two
* arguments: this observable object and <code>null</code>. In other
* words, this method is equivalent to:
* <blockquote><tt>
* notifyObservers(null)</tt></blockquote>
*
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#hasChanged()
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
*/
public void notifyObservers() {
notifyObservers(null);
}
/**
* If this object has changed, as indicated by the
* <code>hasChanged</code> method, then notify all of its observers
* and then call the <code>clearChanged</code> method to indicate
* that this object has no longer changed.
* <p>
* Each observer has its <code>update</code> method called with two
* arguments: this observable object and the <code>arg</code> argument.
*
* @param arg any object.
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#hasChanged()
* @see java.util.Observer#update(java.util.Observable, java.lang.Object)
*/
public void notifyObservers(Object arg) {
/*
* a temporary array buffer, used as a snapshot of the state of
* current Observers.
*/
Object[] arrLocal;
synchronized (this) {
/* We don't want the Observer doing callbacks into
* arbitrary code while holding its own Monitor.
* The code where we extract each Observable from
* the Vector and store the state of the Observer
* needs synchronization, but notifying observers
* does not (should not). The worst result of any
* potential race-condition here is that:
* 1) a newly-added Observer will miss a
* notification in progress
* 2) a recently unregistered Observer will be
* wrongly notified when it doesn't care
*/
if (!changed)
return;
arrLocal = obs.toArray();
clearChanged();
}
for (int i = arrLocal.length-1; i>=0; i--)
((Observer)arrLocal[i]).update(this, arg);
}
/**
* Clears the observer list so that this object no longer has any observers.
*/
public synchronized void deleteObservers() {
obs.removeAllElements();
}
/**
* Marks this <tt>Observable</tt> object as having been changed; the
* <tt>hasChanged</tt> method will now return <tt>true</tt>.
*/
protected synchronized void setChanged() {
changed = true;
}
/**
* Indicates that this object has no longer changed, or that it has
* already notified all of its observers of its most recent change,
* so that the <tt>hasChanged</tt> method will now return <tt>false</tt>.
* This method is called automatically by the
* <code>notifyObservers</code> methods.
*
* @see java.util.Observable#notifyObservers()
* @see java.util.Observable#notifyObservers(java.lang.Object)
*/
protected synchronized void clearChanged() {
changed = false;
}
/**
* Tests if this object has changed.
*
* @return <code>true</code> if and only if the <code>setChanged</code>
* method has been called more recently than the
* <code>clearChanged</code> method on this object;
* <code>false</code> otherwise.
* @see java.util.Observable#clearChanged()
* @see java.util.Observable#setChanged()
*/
public synchronized boolean hasChanged() {
return changed;
}
/**
* Returns the number of observers of this <tt>Observable</tt> object.
*
* @return the number of observers of this object.
*/
public synchronized int countObservers() {
return obs.size();
}
}
最後更新：2017-04-03 16:48:46