初窥设计模式(2)
2016-04-19 15:52
218 查看
2.1装饰模式:装饰模式就是给一个对象增加一些新的功能,而且是动态的,要求装饰对象和被装饰对象实现同一个接口,装饰对象持有被装饰对象的实例
Source类是被装饰类,Decorator类是一个装饰类,可以为Source类动态的添加一些功能,代码如下:
[java] view plaincopy
public interface Sourceable {
public void method();
}
[java] view plaincopy
public class Source implements Sourceable {
@Override
public void method() {
System.out.println("the original method!");
}
}
[java] view plaincopy
public class Decorator implements Sourceable {
private Sourceable source;
public Decorator(Sourceable source){
super();
this.source = source;
}
@Override
public void method() {
System.out.println("before decorator!");
source.method();
System.out.println("after decorator!");
}
}
测试类:
[java] view plaincopy
public class DecoratorTest {
public static void main(String[] args) {
Sourceable source = new Source();
Sourceable obj = new Decorator(source);
obj.method();
}
}
输出:
before decorator!
the original method!
after decorator!
装饰器模式的应用场景:
1、需要扩展一个类的功能。
2、动态的为一个对象增加功能,而且还能动态撤销。(继承不能做到这一点,继承的功能是静态的,不能动态增删。)
缺点:产生过多相似的对象,不易排错!
2.2观察者模式:当一个对象变化时,其它依赖该对象的对象都会收到通知,并且随着变化!对象之间是一种一对多的关系
我解释下这些类的作用:MySubject类就是我们的主对象,Observer1和Observer2是依赖于MySubject的对象,当MySubject变化时,Observer1和Observer2必然变化。AbstractSubject类中定义着需要监控的对象列表,可以对其进行修改:增加或删除被监控对象,且当MySubject变化时,负责通知在列表内存在的对象。我们看实现代码:
一个Observer接口:
[java] view plaincopy
public interface Observer {
public void update();
}
两个实现类:
[java] view plaincopy
public class Observer1 implements Observer {
@Override
public void update() {
System.out.println("observer1 has received!");
}
}
[java] view plaincopy
public class Observer2 implements Observer {
@Override
public void update() {
System.out.println("observer2 has received!");
}
}
Subject接口及实现类:
[java] view plaincopy
public interface Subject {
/*增加观察者*/
public void add(Observer observer);
/*删除观察者*/
public void del(Observer observer);
/*通知所有的观察者*/
public void notifyObservers();
/*自身的操作*/
public void operation();
}
[java] view plaincopy
public abstract class AbstractSubject implements Subject {
private Vector<Observer> vector = new Vector<Observer>();
@Override
public void add(Observer observer) {
vector.add(observer);
}
@Override
public void del(Observer observer) {
vector.remove(observer);
}
@Override
public void notifyObservers() {
Enumeration<Observer> enumo = vector.elements();
while(enumo.hasMoreElements()){
enumo.nextElement().update();
}
}
}
[java] view plaincopy
public class MySubject extends AbstractSubject {
@Override
public void operation() {
System.out.println("update self!");
notifyObservers();
}
}
测试类:
[java] view plaincopy
public class ObserverTest {
public static void main(String[] args) {
Subject sub = new MySubject();
sub.add(new Observer1());
sub.add(new Observer2());
sub.operation();
}
}
输出:
update self!
observer1 has received!
observer2 has received!
Source类是被装饰类,Decorator类是一个装饰类,可以为Source类动态的添加一些功能,代码如下:
[java] view plaincopy
public interface Sourceable {
public void method();
}
[java] view plaincopy
public class Source implements Sourceable {
@Override
public void method() {
System.out.println("the original method!");
}
}
[java] view plaincopy
public class Decorator implements Sourceable {
private Sourceable source;
public Decorator(Sourceable source){
super();
this.source = source;
}
@Override
public void method() {
System.out.println("before decorator!");
source.method();
System.out.println("after decorator!");
}
}
测试类:
[java] view plaincopy
public class DecoratorTest {
public static void main(String[] args) {
Sourceable source = new Source();
Sourceable obj = new Decorator(source);
obj.method();
}
}
输出:
before decorator!
the original method!
after decorator!
装饰器模式的应用场景:
1、需要扩展一个类的功能。
2、动态的为一个对象增加功能,而且还能动态撤销。(继承不能做到这一点,继承的功能是静态的,不能动态增删。)
缺点:产生过多相似的对象,不易排错!
2.2观察者模式:当一个对象变化时,其它依赖该对象的对象都会收到通知,并且随着变化!对象之间是一种一对多的关系
我解释下这些类的作用:MySubject类就是我们的主对象,Observer1和Observer2是依赖于MySubject的对象,当MySubject变化时,Observer1和Observer2必然变化。AbstractSubject类中定义着需要监控的对象列表,可以对其进行修改:增加或删除被监控对象,且当MySubject变化时,负责通知在列表内存在的对象。我们看实现代码:
一个Observer接口:
[java] view plaincopy
public interface Observer {
public void update();
}
两个实现类:
[java] view plaincopy
public class Observer1 implements Observer {
@Override
public void update() {
System.out.println("observer1 has received!");
}
}
[java] view plaincopy
public class Observer2 implements Observer {
@Override
public void update() {
System.out.println("observer2 has received!");
}
}
Subject接口及实现类:
[java] view plaincopy
public interface Subject {
/*增加观察者*/
public void add(Observer observer);
/*删除观察者*/
public void del(Observer observer);
/*通知所有的观察者*/
public void notifyObservers();
/*自身的操作*/
public void operation();
}
[java] view plaincopy
public abstract class AbstractSubject implements Subject {
private Vector<Observer> vector = new Vector<Observer>();
@Override
public void add(Observer observer) {
vector.add(observer);
}
@Override
public void del(Observer observer) {
vector.remove(observer);
}
@Override
public void notifyObservers() {
Enumeration<Observer> enumo = vector.elements();
while(enumo.hasMoreElements()){
enumo.nextElement().update();
}
}
}
[java] view plaincopy
public class MySubject extends AbstractSubject {
@Override
public void operation() {
System.out.println("update self!");
notifyObservers();
}
}
测试类:
[java] view plaincopy
public class ObserverTest {
public static void main(String[] args) {
Subject sub = new MySubject();
sub.add(new Observer1());
sub.add(new Observer2());
sub.operation();
}
}
输出:
update self!
observer1 has received!
observer2 has received!
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