Java设计模式（四）建造者模式

定义：

建造者模式：将一个复杂的对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示。

角色：

在这样的设计模式中，有以下几个角色：

1. Builder：为创建一个产品对象的各个部件指定抽象接口。
2. ConcreteBuilder：实现Builder的接口以构造和装配该产品的各个部件，定义并明确它所创建的表示，并提供一个检索产品的接口。
3. Director：构造一个使用Builder接口的对象，指导构建过程。
4. Product：表示被构造的复杂对象。ConcreteBuilder创建该产品的内部表示并定义它的装配过程，包含定义组成部件的类，包括将这些部件装配成最终产品的接口。

实例：

（不得不说自己画的UML还真是蠢，还是直接上代码吧……）

package Builder;

public interface Item {
    String name();
	int price();
	Packing packing();
}

package Builder;

public abstract class Burger implements Item {
    public abstract String name();
	public abstract int price();
	public Packing packing(){return new Wrapper();}	
}

class Vegburger extends Burger{
	public String name(){return "vegburger";}
	public int price(){return 10;}
}

class Checkburger extends Burger{
	public String name(){return "checkburger";}
	public int price(){return 20;}
		
}

package Builder;

public abstract class Drink  implements Item{
    public abstract String name();
	public abstract int price();
	public Packing packing(){return new Buttle();}
}

class ColdDrink extends Drink{
	public String name(){return "colddrink";}
	public int price(){return 3;}
		
}

class HotDrink extends Drink{
	public String name(){return "hotdrink";}
	public int price(){return 6;}
}

package Builder;

public interface Packing {
	String pack();
}

class Wrapper implements Packing{
	public String pack(){return "wrapper";}
}

class Buttle implements Packing{
	public String pack(){return "buttle";}
}

package Builder;

import java.util.ArrayList;
import java.util.List;

public class Meal {
	List<Item> list = new ArrayList<Item>();
	public void show(){
		for(Item it:list){
			System.out.print(it.name());
			System.out.print("," +it.price());
			System.out.print(","+it.packing().pack());
			System.out.println();
		}

	}
}

package Builder;

public class MealBuilder {
	static int totalcost;
	public void vegmeal() throws InstantiationException, IllegalAccessException{
		Meal meal = new Meal();
		int cost=0;
		meal.list.add(new Vegburger());
		cost += Vegburger.class.newInstance().price();
		meal.list.add(new Vegburger());
		cost += Vegburger.class.newInstance().price();
		meal.list.add(new HotDrink());
		cost += HotDrink.class.newInstance().price();
		System.out.println("show vegmeal");
		meal.show();
		System.out.println("vegmeal花了"+ cost);
		System.out.println();
		totalcost += cost;
	}	
	public void nonvegmeal() throws InstantiationException, IllegalAccessException{
		Meal meal = new Meal();
		int cost=0;
		meal.list.add(new Checkburger());
		cost += Checkburger.class.newInstance().price();
		meal.list.add(new Checkburger());
		cost += Checkburger.class.newInstance().price();
		meal.list.add(new ColdDrink());
		cost += ColdDrink.class.newInstance().price();
		System.out.println("show nonvegmeal");
		meal.show();
		System.out.println("nonvegmeal花了"+ cost);
		System.out.println();
		totalcost += cost;
	}	
}

package Builder;

public class Client {
	public static void main(String[] args) throws InstantiationException, IllegalAccessException{
		MealBuilder mb = new MealBuilder();
		mb.vegmeal();
		mb.vegmeal();
		mb.nonvegmeal();
		System.out.println("一共花了"+mb.totalcost +"元");
	}
}

//输出结果：
show vegmeal
vegburger,10,wrapper
vegburger,10,wrapper
hotdrink,6,buttle
vegmeal花了26

show vegmeal
vegburger,10,wrapper
vegburger,10,wrapper
hotdrink,6,buttle
vegmeal花了26

show nonvegmeal
checkburger,20,wrapper
checkburger,20,wrapper
colddrink,3,buttle
nonvegmeal花了43

一共花了95元