倘若,有这么一个需求,对于一个数字,如果是负的,那么需要变成正的相反数,如果是2的倍数,那么就除以2,如果是3的倍数,那么就除以3,可能以后还有其他的需求,比如是5的倍数,就再除以5,或者是6的倍数,那么就加上6,也就是结果与顺序息息相关,那么应该如何来实现呢?
如果写一个类的方法,按照这个需求来写if语句,可以,但是,如果有两套定制的呢?一套需要其中的几种变化,另外需要另外几种,那么就需要2个方法,而且其中有很多的重复代码,这样行不通的.
其实设计模式说到底,其根本思想就是找到变化并封装之.这里变化的是处理的方法,那么我们就把它封装起来.实现的类如下:
package decorater;
public class Integor {
private Integer x;
public Integer getX() {
return x;
}
public void setX(Integer x) {
this.x = x;
}
Integor(Integer x){
this.x = x;
}
}
由于Integer不能修改传递的值,所以写一个类来封装一个integer
/**
*
*/
package decorater;
public abstract class Decorater {
private Decorater next;
public Decorater setNext(Decorater dcrtr) {
this.next = dcrtr;
return this.next;
}
public void process(Integor x) {
this.executeBefore(x);
if (this.next != null) {
this.next.process(x);
}
this.executeAfter(x);
}
protected abstract void executeBefore(Object x);
protected abstract void executeAfter(Object x);
}
每个实现的类只需要来实现executeBefore和executeAfter方法即可.
注意实现的顺序是
decorater1.executeBefore->decorater2.executeBefore->decorater3.executeBefore->decorater3.executeAfter->decorater2.executeAfter->decorater1.executerAfter
package decorater;
public class PositiveDecorater extends Decorater {
@Override
protected void executeAfter(Object x) {
System.out.println("PositiveDecorater end!");
}
@Override
protected void executeBefore(Object x) {
// TODO Auto-generated method stub
System.out.println("starting PositiveDecorater!");
Integor in = (Integor) x;
if (in.getX() < 0)
in.setX(-in.getX());
}
}
package decorater;
public class Devide2Decorater extends Decorater {
@Override
protected void executeAfter(Object x) {
System.out.println("Devide2Decorater end!");
}
@Override
protected void executeBefore(Object x) {
System.out.println("Starting Devide2Decorater!");
Integor in = (Integor) x;
if (in.getX() % 2 == 0) {
in.setX(in.getX() / 2);
}
}
}
package decorater;
public class Devide3Decorater extends Decorater {
@Override
protected void executeAfter(Object x) {
System.out.println("Devide3Decorater end!");
}
@Override
protected void executeBefore(Object x) {
System.out.println("Starting Devide3Decorater!");
Integor in = (Integor) x;
if (in.getX() % 3 == 0) {
in.setX(in.getX() / 3);
}
}
}
/**
*
*/
package decorater;
/**
* @author KONGHE
*
*/
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
Decorater a = new PositiveDecorater();
a.setNext(new Devide2Decorater()).setNext(new Devide3Decorater());
Integor x = new Integor(-18);
a.process(x);
System.out.println(x.getX());
}
}
输出结果是:
starting PositiveDecorater!
Starting Devide2Decorater!
Starting Devide3Decorater!
Devide3Decorater end!
Devide2Decorater end!
PositiveDecorater end!
3
其实每种设计模式的核心思想都是一致的,但是没有必要照本宣科,只要注意其模式的精髓,就可以了,剩下的就是自己去按照实现来设计其中的细节了.比如我设计这个模式,就是先写了main函数,把其中的方法写好,然后去按照这个实现来想去如何实现,这样才更符合解决实际的问题.其实decorater模式有很多种实现方式.比如下面的这种解法,也可:
/**
*
*/
package decorator;
/**
* @author KONGHE
*
*/
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
DecoraterChain a = new DecoraterChain();
a.setNext(new PositiveDecorater()).setNext(new Devide2Decorater()).setNext(new Devide3Decorater());
Integer x = -32;
x = a.process(x);
System.out.println(x);
}
}
/**
*
*/
package decorator;
import java.util.ArrayList;
import java.util.List;
/**
* @author KONGHE
*
*/
public class DecoraterChain {
private List<Decorater> decorater = new ArrayList<Decorater>();
public DecoraterChain setNext(Decorater decrter) {
decorater.add(decrter);
return this;
}
public Integer process(Integer x) {
for (int i = 0; i < this.decorater.size(); i++) {
x = this.decorater.get(i).process(x);
}
return x;
}
}
/**
*
*/
package decorator;
/**
* @author KONGHE
*
*/
public abstract class Decorater {
public abstract Integer process(Integer x);
}
总而言之,模式是为了具体的实际情况而服务的,不要为了一定要去用某种设计模式而委屈自己的需求.
在设计的时候多想想,可能某天你再读设计模式的书,你会发现,原来我之前写的代码,包含了这么多的设计模式啊!