模式介绍
建造者模式(Builder Pattern)使用多个简单的对象一步一步构建成一个复杂的对象,主要解决在软件系统中,有时候面临着"一个复杂对象"的创建工作,其通常由各个部分的子对象用一定的算法构成;由于需求的变化,这个复杂对象的各个部分经常面临着剧烈的变化,但是将它们组合在一起的算法却相对稳定。
模式组成部分
- Product (产品类):是一个较为复杂的类,给这个类创建对象的过程比较复杂,会有比较多的代码量。
- Abstract Builder (抽象建造者):引入抽象建造者的目的,是为了将建造的具体过程交与它的子类来实现。这样更容易扩展。一 般至少会有两个抽象方法,一个用来建造产品,一个是用来返回产品。
- ConcreteBuilder (具体建造者):实现抽象类的所有未实现的方法,具体来说一般是两项任务:组建产品,返回组建好的产品。
- Director (资源调动者):负责调用适当的建造者来组建产品,资源调动者一般不与产品类发生依赖关系,与资源调动者直接交互的是建造者类。一般来说,资源调动者被用来封装程序中易变的部分。
代码
/** "Product" */
class Pizza {
private String dough = "";
private String sauce = "";
private String topping = "";
public void setDough (String dough) { this.dough = dough; }
public void setSauce (String sauce) { this.sauce = sauce; }
public void setTopping (String topping) { this.topping = topping; }
}
/** "Abstract Builder" */
abstract class PizzaBuilder {
protected Pizza pizza;
public Pizza getPizza() { return pizza; }
public void createNewPizzaProduct() { pizza = new Pizza(); }
public abstract void buildDough();
public abstract void buildSauce();
public abstract void buildTopping();
}
/** "ConcreteBuilder" */
class HawaiianPizzaBuilder extends PizzaBuilder {
public void buildDough() { pizza.setDough("cross"); }
public void buildSauce() { pizza.setSauce("mild"); }
public void buildTopping() { pizza.setTopping("ham+pineapple"); }
}
/** "ConcreteBuilder" */
class SpicyPizzaBuilder extends PizzaBuilder {
public void buildDough() { pizza.setDough("pan baked"); }
public void buildSauce() { pizza.setSauce("hot"); }
public void buildTopping() { pizza.setTopping("pepperoni+salami"); }
}
/** "Director" */
class Waiter {
private PizzaBuilder pizzaBuilder;
public void setPizzaBuilder (PizzaBuilder pb) { pizzaBuilder = pb; }
public Pizza getPizza() { return pizzaBuilder.getPizza(); }
public void constructPizza() {
pizzaBuilder.createNewPizzaProduct();
pizzaBuilder.buildDough();
pizzaBuilder.buildSauce();
pizzaBuilder.buildTopping();
}
}
/** A customer ordering a pizza. */
class BuilderExample {
public static void main(String[] args) {
Waiter waiter = new Waiter();
PizzaBuilder hawaiian_pizzabuilder = new HawaiianPizzaBuilder();
PizzaBuilder spicy_pizzabuilder = new SpicyPizzaBuilder();
waiter.setPizzaBuilder ( hawaiian_pizzabuilder );
waiter.constructPizza();
Pizza pizza = waiter.getPizza();
}
}