设计模式：装饰者

首先用IO实现一下将读取的所有英文字母转成小写。

import java.io.*;

public class LowerCaseInputStream extends FilterInputStream {

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

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

public int read(byte[] b, int offset, int len) throws IOException {
int result = in.read(b, offset, len);
for (int i = offset; i < offset+result; i++) {
b[i] = (byte)Character.toLowerCase((char)b[i]);
}
return result;
}
}

public class InputTest {
public static void main(String[] args) throws IOException {
int c;

try {
InputStream in =
new LowerCaseInputStream(
new BufferedInputStream(
new FileInputStream("test.txt")));

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

in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

由此就可在不改变原有对象（不在原类中添加方法）的情况下，满足上述要求。

下面，将用星巴克咖啡为例子说明装饰者模式。

首先，先定义一个超类：饮料。

public abstract class Beverage {
String description = "Unknown Beverage";

public String getDescription() {
return description;
}

public abstract double cost();
}

然后定义一个超类，要往饮料里面添加的佐料

public abstract class CondimentDecorator extends Beverage {
public abstract String getDescription();
}

定义一种饮料 黑玫瑰

public class DarkRoast extends Beverage {
public DarkRoast() {
description = "Dark Roast Coffee";
}

public double cost() {
return .99;
}
}

另一种饮料 Decaf

public class Decaf extends Beverage {
public Decaf() {
description = "Decaf Coffee";
}

public double cost() {
return 1.05;
}
}

又一种饮料

public class Espresso extends Beverage {

public Espresso() {
description = "Espresso";
}

public double cost() {
return 1.99;
}
}

还是一种饮料

public class HouseBlend extends Beverage {
public HouseBlend() {
description = "House Blend Coffee";
}

public double cost() {
return .89;
}
}

接下来是搭配的一些佐料，流奶。

public class Milk extends CondimentDecorator {
Beverage beverage;

public Milk(Beverage beverage) {
this.beverage = beverage;
}

public String getDescription() {
return beverage.getDescription() + ", Milk";
}

public double cost() {
return .10 + beverage.cost();
}
}

摩卡

public class Mocha extends CondimentDecorator {
Beverage beverage;

public Mocha(Beverage beverage) {
this.beverage = beverage;
}

public String getDescription() {
return beverage.getDescription() + ", Mocha";
}

public double cost() {
return .20 + beverage.cost();
}
}

public class Soy extends CondimentDecorator {
Beverage beverage;

public Soy(Beverage beverage) {
this.beverage = beverage;
}

public String getDescription() {
return beverage.getDescription() + ", Soy";
}

public double cost() {
return .15 + beverage.cost();
}
}

public class Whip extends CondimentDecorator {
Beverage beverage;

public Whip(Beverage beverage) {
this.beverage = beverage;
}

public String getDescription() {
return beverage.getDescription() + ", Whip";
}

public double cost() {
return .10 + beverage.cost();
}
}

准备好这些，咖啡店可以开张了。

public static void main(String args[]) {
Beverage beverage = new Espresso();
System.out.println(beverage.getDescription()
+ " $" + beverage.cost());

Beverage beverage2 = new DarkRoast();
beverage2 = new Mocha(beverage2);
beverage2 = new Moch
3ff0
a(beverage2);
beverage2 = new Whip(beverage2);
System.out.println(beverage2.getDescription()
+ " $" + beverage2.cost());

Beverage beverage3 = new HouseBlend();
beverage3 = new Soy(beverage3);
beverage3 = new Mocha(beverage3);
beverage3 = new Whip(beverage3);
System.out.println(beverage3.getDescription()
+ " $" + beverage3.cost());
}
}

以上例子中，不断对同一种饮料加其他东西（用装饰者进行包装。改变对象的原本属性。）特点就是不改变原对象的任何属性！！