设计模式--装饰者模式

1.定义

动态的将责任附加到对象上，若要扩展功能，装饰者提供了 比继承者更有弹性的替代方案。

装饰者和被装饰者必须是一样的类型。所以有共同的超类。

利用继承同一个超类,达到“类型匹配”，而不是利用继承获得行为。

装饰者要做的事，就是增加行为到被装饰者（即包装对象）上。

2. 自定义装饰者模式实现



实现代码如下：

//抽象超类

public abstract class BaseComponent {

protected String description = "Unknown";

public abstract double cost();

public String getDescription() {
return description;
}

}

//鱼，肉类 = 被包装对象 = 被装饰者

public class Fish extends BaseComponent {

public Fish(){
description = "fish";
}

@Override
public double cost() {
return 100;

}

}

public class Meat extends BaseComponent{

public Meat(){
description = "meat";
}

@Override
public double cost() {
return 200;
}

}

//装饰者抽象类(装饰者的基类)

public abstract class Condiment extends BaseComponent{

public abstract String getDescription();

}

// 装饰者 辣椒 麻油 糖

public class ChilliCondiment extends Condiment {

private BaseComponent base;

public ChilliCondiment(BaseComponent base){
this.base = base;
}

@Override
public String getDescription() {
// TODO Auto-generated method stub
return base.getDescription() + ", 辣椒";
}

@Override
public double cost() {
// TODO Auto-generated method stub
return base.cost() + 10;
}

}

public class CastOilCondiment extends Condiment{

private BaseComponent base;

public CastOilCondiment(BaseComponent base){
this.base = base;
}

@Override
public String getDescription() {
// TODO Auto-generated method stub
return base.getDescription() + ", 麻油";
}

@Override
public double cost() {
// TODO Auto-generated method stub
return base.cost() + 20;
}

}

public class SugarCondiment extends Condiment{

private BaseComponent base;

public SugarCondiment(BaseComponent base){
this.base = base;
}

@Override
public String getDescription() {
// TODO Auto-generated method stub
return base.getDescription() + ", 糖";
}

@Override
public double cost() {
// TODO Auto-generated method stub
return base.cost() + 30;
}

}

测试代码：

public class MainTest {

public static void main(String[] args) throws IOException {

BaseComponent menu1 = new Fish();
menu1 = new ChilliCondiment(menu1);
menu1 = new CastOilCondiment(menu1);
System.out.println(menu1.getDescription() + menu1.cost());

BaseComponent menu2 = new Meat();
menu2 = new ChilliCondiment(menu2);
menu2 = new SugarCondiment(menu2);
System.out.println(menu2.getDescription() + menu2.cost());

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｝

运行结果如下:

fish, 辣椒, 麻油130.0

meat, 辣椒, 糖240.0

3. java内置装饰者模式， java.io



实例代码如下：

//包装类，继承FilterInputStream

public class LowerCaseInputStream extends FilterInputStream{

protected LowerCaseInputStream(InputStream in) {
super(in);
}

@Override
public int read() throws IOException {
int c = super.read();
return c == -1 ? c : Character.toLowerCase((char)c);
}

@Override
public int read(byte[] b, int off, int len) throws IOException {
int result = super.read(b, off, len);
for(int i=0;i<b.length;i++){
b[i] = (byte)Character.toLowerCase((char) b[i]);
}
return result;
}

}

<
4000
p>

测试代码如下：

public class MainTest {

public static void main(String[] args) throws IOException {

InputStream in = new LowerCaseInputStream(new BufferedInputStream(new FileInputStream("c:/test.txt")));

int c ;
while((c = in.read()) >=0){
System.out.print((char)c);
}

in.close();

}

}

OO原则： 

封装变化

多用组合，少用继承

针对接口编程，不针对实现编程

为交互对象之间的松耦合设计而努力

对扩展开放，对修改封闭