设计模式2--装饰模式（the decorator design pattern）

允许多次实现一种方法，避免每次改动代码。

没有使用装饰模式：

Computer description()
Computer new_description()
Computer newer_description()

使用了装饰模式：

Computer description()


Computer description()
Disk description()


Computer description()
Disk description()
Monitor description()

public class Computer
{
	public Computer(){}
	
	public String description() {
		return "You're getting a computer.";
	}
}

public class Computer
{
	public Computer(){}
	
	public String description() {
		return "You're getting a computer and a disk.";
	}
}

public class Computer
{
	public Computer(){}
	
	public String description() {
		return "You're getting a computer and a disk and a monitor.";
	}
}


public class Computer
{
	public Computer(){}
	
	public String description() {
		return "computer";
	}
}

public abstract class ComponentDecorator extends Computer
{
	public abstract String description();
}

public class Disk extends ComponentDecorator
{
	Computer computer;
	
	public Disk(Computer c)
	{
		computer = c;
	}
	
	public String description()
	{
		return computer.description()+" and a disk";
	}
}

public class Monitor extends ComponentDecorator
{
	Computer computer;
	
	public Monitor(Computer c)
	{
		computer = c;
	}
	
	public String description()
	{
		return computer.description()+" and a monitor";
	}
}

public class Test
{
	public static void main(String args[]) {
		Computer computer = new Computer();
		computer = new Disk(computer);
		computer = new Monitor(computer);
		computer = new Monitor(computer);
		System.out.println("You're getting a " + computer.description() + ".");	
	}
}