第五章 装饰模式

一，何为装饰模式？

其目的是包装一个目标对象，从而可以在运行时动态添加新的职责。每个装饰器都可以包装另一个装饰器，这样从理论上来说可以对目标对象进行无限次的修饰

二，用普通代码实现装饰模式

//Order接口
public interface Order {
	public double getPrice();

	public String getLabel();
}
//被装饰的类要实现Order接口
public class Pizza implements Order {
	private String label;
	private double price;

	public Pizza(String label, double price) {
		this.label = label;
		this.price = price;
	}

	public double getPrice() {
		return this.price;
	}

	public String getLabel() {
		return this.label;
	}
}

如下用代码创建了一个披萨

Order pizza = new Pizza("newPizza",10);

接下来需要创建一个装饰器，它会通过额外的配料来装饰披萨。这里使用了一个抽象类，这样具体类就不必实现接口中所有的业务方法了。抽象装饰器会创建一个可供其它装饰器继承的蓝图

抽象装饰器

ublic abstract class Extra implements Order {
	protected Order order;
	protected String label;
	protected double price;

	public Extra(String label, double price, Order order) {
		this.label = label;
		this.price = price;
		this.order = order;
	}

	// Price can be a big issue, so delegate this to concrete implementation
	public abstract double getPrice();

	// Should be okay to provide standard labeling
	public String getLabel() {
		return order.getLabel() + ", " + this.label;
	}
}

创建具体装饰器1

public class RegularExtra extends Extra {
	public RegularExtra(String label, double price, Order order) {
		super(label, price, order);
	}

	public double getPrice() {
		return this.price + order.getPrice();
	}
}

创建具体装饰器2

public class NoCostExtra extends Extra {
	public NoCostExtra(String label, double price, Order order) {
		super(label, price, order);
	}

	public double getPrice() {
		return order.getPrice();
	}
}

创建具体装饰器3

public class DoubleExtra extends Extra {
public DoubleExtra(String label, double price, Order order) {
super(label, price, order);
}
public double getPrice() {
return (this.price*2)+order.getPrice();
}
public String getLabel() {
return order.getLabel()+ ", Double " + this.label;
}
}

测试

Order fourSeasonsPizza = new Pizza("Four Seasons Pizza", 10);
fourSeasonsPizza = new RegularExtra("Pepperoni", 4, fourSeasonsPizza );
fourSeasonsPizza = new DoubleExtra("Mozzarella", 2, fourSeasonsPizza );
fourSeasonsPizza = new NoCostExtra("Chili", 2, fourSeasonsPizza );
System.out.println(fourSeasonsPizza.getPrice());
System.out.println(fourSeasonsPizza.getLabel());