无涯教程-Java 建造者模式

无涯教程
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构建器模式(Builder Pattern)使用简单对象并使用逐步方法来构建复杂对象，这种设计模式属于创建模式，Builder类逐步构建最终对象。

建造者模式实例

无涯教程考虑了一家快餐店的商业案例，其中典型的一餐可能是汉堡和冷饮。汉堡可以是蔬菜汉堡或鸡肉汉堡，并且可以用包装纸包装。冷饮可以是可乐或百事可乐，可以装在瓶中。

将创建一个 Item 接口，该接口代表诸如汉堡和冷饮之类的食品，以及实现 Item 接口和 Package 接口的具体类，食品的包装和实现包装接口的具体类，如将汉堡包装在包装纸中，将冷饮包装在瓶中。

然后，创建一个 Meal 类，该类具有 Item 的 ArrayList 和一个 MealBuilder 来构建不同类型的 Meal 对象(通过组合 Item ) ，演示类将使用 MealBuilder 来构建 Meal 。

Builder Pattern UML Diagram

第1步  -  创建一个代表食品和包装的物料接口。

Item.java 

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

Packing.java 

public interface Packing {
   public String pack();
}

第2步  -  创建实现Packing接口的具体类。

Wrapper.java 

public class Wrapper implements Packing {

@Override
public String pack() {
return "Wrapper";
}
}

Bottle.java 

public class Bottle implements Packing {

@Override
public String pack() {
return "Bottle";
}
}

第3步  -  创建实现提供默认函数的item接口的抽象类。

Burger.java 

public abstract class Burger implements Item {

@Override
public Packing packing() {
return new Wrapper();
}


@Override
public abstract float price();
}

ColdDrink.java 

public abstract class ColdDrink implements Item {

</span><span class="lit">@Override</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="typ">Packing</span><span class="pln"> packing</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">return</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Bottle</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">

</span><span class="lit">@Override</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">abstract</span><span class="pln"> </span><span class="kwd">float</span><span class="pln"> price</span><span class="pun">();</span><span class="pln">



}

第4步  -  创建扩展Burger和ColdDrink类的具体类

VegBurger.java 

public class VegBurger extends Burger {

@Override
public float price() {
return 25.0f;
}


@Override
public String name() {
return "Veg Burger";
}
}

ChickenBurger.java 

public class ChickenBurger extends Burger {

@Override
public float price() {
return 50.5f;
}


@Override
public String name() {
return "Chicken Burger";
}
}

Coke.java 

public class Coke extends ColdDrink {

@Override
public float price() {
return 30.0f;
}


@Override
public String name() {
return "Coke";
}
}

Pepsi.java 

public class Pepsi extends ColdDrink {

@Override
public float price() {
return 35.0f;
}


@Override
public String name() {
return "Pepsi";
}
}

第5步  -  创建具有上面定义的Item对象的Meal类。

Meal.java 

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

public class Meal {
private List<Item> items=new ArrayList<Item>();


public void addItem(Item item){
items.add(item);
}


public float getCost(){
float cost=0.0f;


  </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="typ">Item</span><span class="pln"> item </span><span class="pun">:</span><span class="pln"> items</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     cost </span><span class="pun">+=</span><span class="pln"> item</span><span class="pun">.</span><span class="pln">price</span><span class="pun">();</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">		
  </span><span class="kwd">return</span><span class="pln"> cost</span><span class="pun">;</span><span class="pln">



}


public void showItems(){


  </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="typ">Item</span><span class="pln"> item </span><span class="pun">:</span><span class="pln"> items</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Item : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> item</span><span class="pun">.</span><span class="pln">name</span><span class="pun">());</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">", Packing : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> item</span><span class="pun">.</span><span class="pln">packing</span><span class="pun">().</span><span class="pln">pack</span><span class="pun">());</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">", Price : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> item</span><span class="pun">.</span><span class="pln">price</span><span class="pun">());</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">		



}
}

第6步  -  创建一个MealBuilder类，实际的构建器类负责创建Meal对象。

MealBuilder.java 

public class MealBuilder {

public Meal prepareVegMeal (){
Meal meal=new Meal();
meal.addItem(new VegBurger());
meal.addItem(new Coke());
return meal;
}


public Meal prepareNonVegMeal (){
Meal meal=new Meal();
meal.addItem(new ChickenBurger());
meal.addItem(new Pepsi());
return meal;
}
}

第7步  -  BuiderPatternDemo使用MealBuider演示了构建器模式。

BuilderPatternDemo.java 

public class BuilderPatternDemo {
   public static void main(String[] args) {

  </span><span class="typ">MealBuilder</span><span class="pln"> mealBuilder</span><span class="pun">=</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">MealBuilder</span><span class="pun">();</span><span class="pln">

  </span><span class="typ">Meal</span><span class="pln"> vegMeal</span><span class="pun">=</span><span class="pln">mealBuilder</span><span class="pun">.</span><span class="pln">prepareVegMeal</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Veg Meal"</span><span class="pun">);</span><span class="pln">
  vegMeal</span><span class="pun">.</span><span class="pln">showItems</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Total Cost: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> vegMeal</span><span class="pun">.</span><span class="pln">getCost</span><span class="pun">());</span><span class="pln">

  </span><span class="typ">Meal</span><span class="pln"> nonVegMeal</span><span class="pun">=</span><span class="pln">mealBuilder</span><span class="pun">.</span><span class="pln">prepareNonVegMeal</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"\n\nNon-Veg Meal"</span><span class="pun">);</span><span class="pln">
  nonVegMeal</span><span class="pun">.</span><span class="pln">showItems</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Total Cost: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> nonVegMeal</span><span class="pun">.</span><span class="pln">getCost</span><span class="pun">());</span><span class="pln">



}
}

第8步  -  验证输出。

Veg Meal
Item : Veg Burger, Packing : Wrapper, Price : 25.0
Item : Coke, Packing : Bottle, Price : 30.0
Total Cost: 55.0

Non-Veg Meal
Item : Chicken Burger, Packing : Wrapper, Price : 50.5
Item : Pepsi, Packing : Bottle, Price : 35.0
Total Cost: 85.5

参考链接

www.learnfk.com/design-patt…

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