觀察者模式涉及到2個對象:觀察者和被觀察者
但是並不是觀察者時時觀察着被觀察者,而是被觀察者改變時通知觀察它的觀察者。
所以更傾向於叫它:訂閱播報模式。
訂閱後當有更新的時候主動通知訂閱者
/**
* 觀察者(訂閱者)接口
* @author Administrator
*
*/
public interface Observer {
public void notify();
}
public class Student implements Obser{
@Override
public void update() {
// TODO Auto-generated method stub
System.out.println("我知道書單更新了");
}
}
//被觀察者
public interface Oberverle {
public void addObser(Obser o);
public void removeObser(Obser o);
public void notify();
}
public class Book implements Oberverle{
List<Obser> list;
public Book() {
// TODO Auto-generated constructor stub
list=new ArrayList<>();
}
@Override
public void addObser(Obser o) {
// TODO Auto-generated method stub
list.add(o);
}
@Override
public void removeObser(Obser o) {
// TODO Auto-generated method stub
list.remove(o);
}
@Override
public void update() {
// TODO Auto-generated method stub
for (Obser obser : list) {
obser.update();
}
}
}
//測試
public class Test {
public static void main(String[] args) {
Student s=new Student();
Book b=new Book();
b.addObser(s);
//b.removeObser(s);
b.update();
}
}
以下百度百科
//觀察者,需要用到觀察者模式的類需實現此接口
public interface Observer{
void update(Object...objs);
}
//被觀察者(一個抽象類,方便擴展)
public abstract class Observable{
public final ArrayList<Class<?>> obserList = new ArrayList<Class<?>>();
/**AttachObserver(通過實例註冊觀察者)
*<b>Notice:</b>obcan'tbenull,oritwillthrowNullPointerException
**/
public<T> void registerObserver(T ob){
if(ob==null) throw new NullPointerException();
this.registerObserver(ob.getClass());
}
/**
*AttachObserver(通過Class註冊觀察者)
*@paramcls
*/
public void registerObserver(Class<?> cls){
if(cls==null) throw new NullPointerException();
synchronized(obserList){
if(!obserList.contains(cls)){
obserList.add(cls);
}
}
}
/**UnattachObserver(註銷觀察者)
*<b>Notice:</b>
*<b>ItreverseswithattachObserver()method</b>
**/
public<T>void unRegisterObserver(Tob){
if(ob==null) throw new NullPointerException();
this.unRegisterObserver(ob.getClass());
}
/**UnattachObserver(註銷觀察者,有時候在未獲取到實例使用)
*<b>Notice:</b>
*<b>ItreverseswithattachObserver()method</b>
**/
public void unRegisterObserver(Class<?>cls){
if(cls==null) throw new NullPointerException();
synchronized(obserList){
Iterator<Class<?>>iterator=obserList.iterator();
while(iterator.hasNext()){
if(iterator.next().getName().equals(cls.getName())){
iterator.remove();
break;
}
}
}
}
/**detachallobservers*/
public void unRegisterAll(){
synchronized(obserList){
obserList.clear();
}
}
/**Ruturnthesizeofobservers*/
public int countObservers(){
synchronized(obserList){
returnobserList.size();
}
}
/**
*notify all observer(通知所有觀察者,在子類中實現)
*@paramobjs
*/
public abstract void notifyObservers(Object... objs);
/**
*notify one certain observer(通知某一個確定的觀察者)
*@paramcls
*@paramobjs
*/
public abstract void notifyObserver(Class<?> cls, Object... objs);
/**
*notifyonecertainobserver
*@paramcls
*@paramobjs
*/
public abstract<T> void notifyObserver(T t, Object... objs);
}
//目標被觀察者
public class ConcreteObservable extends Observable{
private static ConcreteObservableinstance = null;
private ConcreteObservable(){};
public static synchronized ConcreteObservablegetInstance(){
if(instance == null){
instance=newConcreteObservable();
}
returninstance;
}
@Override
public <T> void notifyObserver(T t, Object... objs){
if(t == null) throw new NullPointerException();
this.notifyObserver(t.getClass(), objs);
}
@Override
public void notifyObservers(Object... objs){
for(Class<?>cls : obserList){
this.notifyObserver(cls, objs);
}
}
//通過java反射機制實現調用
@Override
public void notifyObserver(Class<?>cls, Object...objs){
if(cls == null) throw new NullPointerException();
Method[] methods = cls.getDeclaredMethods();
for(Method method : methods){
if(method.getName().equals("update")){
try{
method.invoke(cls,objs);
break;
}catch(IllegalArgumentException e){
e.printStackTrace();
}catch(IllegalAccessException e){
e.printStackTrace();
}catch(InvocationTargetException e){
e.printStackTrace();
}
}
}
}
}
//使用(實現Observer接口)
public class Text extends Activity implements Observer{
publicvoidonCreate(...){
ConcreteObservable.getInstance().registerObserver(Text.class);
....
}
//實現接口處理
publicvoidupdate(Object...objs){
//做操作,比如更新數據,更新UI等
}
}
重點內容