设计模式：创建型模式：建造模式（Builder Pattern）

来源：互联网发布：胡歌人品知乎编辑：程序博客网时间：2024/05/01 01:04

本文是下面文章的剪辑，深表感谢：

1）Builder模式的误区：将复杂对象的构建进行封装，就是Builder模式了吗？ http://www.cnblogs.com/happyhippy/archive/2010/09/01/1814287.html

2）深入浅出设计模式 by AI92

3）Example of `builder' design pattern in C++ https://gist.github.com/pazdera/1121152

根据UML，整个过程有4个类参与

1）抽象建造者角色：这个角色用来规范产品对象的各个组成成分的建造。一般而言，此角色独立于应用程序的业务逻辑；

2）具体建造者角色：担任这个角色的是于应用程序紧密相关的类，它们在指导者的调用下创建产品实例。这个角色在实现抽象建造者角色提供的方法的前提下，达到完成产品组装，提供成品的功能；

3）指导者角色：调用具体建造者角色以创建产品对象。指导者并没有产品类的具体知识，真正拥有产品类的具体知识的是具体建造者对象。

4）产品角色：建造中的复杂对象。它要包含那些定义组件的类，包括将这些组件装配成产品的接口。

首先客户程序创建一个指导者对象，一个建造者角色，并将建造者角色传入指导者对象进行配置。然后，指导者按照步骤调用建造者的方法创建产品。最后客户程序从建造者或者指导者那里得到产品。从建造模式的工作流程来看，建造模式将产品的组装“外部化”到了建造者角色中来。这是和任何正规的工厂模式不一样的——产品的创建是在产品类中完成的。

代码例子：车

* Example of `builder' design pattern.

* Copyright (C) 2011 Radek Pazdera

* This program is free software: you can redistribute it and/or modify

* it under the terms of the GNU General Public License as published by

* the Free Software Foundation, either version 3 of the License, or

* (at your option) any later version.

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

* You should have received a copy of the GNU General Public License

* along with this program. If not, see <http://www.gnu.org/licenses/>.

*/

#include <iostream>

#include <string>

/* Car parts */

class Wheel

public:

    int size;

};

class Engine

public:

    int horsepower;

};

class Body

public:

    std::string shape;

};

/* Final product -- a car */

class Car

public:

    Wheel* wheels[4];

    Engine* engine;

    Body* body;

    void specifications()

        std::cout << "body:" << body->shape << std::endl;

        std::cout << "engine horsepower:" << engine->horsepower << std::endl;

        std::cout << "tire size:" << wheels[0]->size << "'" << std::endl;

};

/* Builder is responsible for constructing the smaller parts */

class Builder

public:

    virtual Wheel* getWheel() = 0;

    virtual Engine* getEngine() = 0;

    virtual Body* getBody() = 0;

};

/* Director is responsible for the whole process */

class Director

private:

    Builder* builder;

public:

    void setBuilder(Builder* newBuilder)

        builder = newBuilder;

    Car* getCar()

        Car* car = new Car();

        car->body = builder->getBody();

        car->engine = builder->getEngine();

        car->wheels[0] = builder->getWheel();

        car->wheels[1] = builder->getWheel();

        car->wheels[2] = builder->getWheel();

        car->wheels[3] = builder->getWheel();

        return car;

};

/* Concrete Builder for Jeep SUV cars */

class JeepBuilder : public Builder

public:

    Wheel* getWheel()

        Wheel* wheel = new Wheel();

        wheel->size = 22;

        return wheel;

    Engine* getEngine()

        Engine* engine = new Engine();

        engine->horsepower = 400;

        return engine;

    Body* getBody()

        Body* body = new Body();

        body->shape = "SUV";

        return body;

};

/* Concrete builder for Nissan family cars */

class NissanBuilder : public Builder

public:

    Wheel* getWheel()

        Wheel* wheel = new Wheel();

        wheel->size = 16;

        return wheel;

    Engine* getEngine()

        Engine* engine = new Engine();

        engine->horsepower = 85;

        return engine;

    Body* getBody()

        Body* body = new Body();

        body->shape = "hatchback";

        return body;

};

int main()

    Car* car; // Final product

    /* A director who controls the process */

    Director director;

    /* Concrete builders */

    JeepBuilder jeepBuilder;

    NissanBuilder nissanBuilder;

    /* Build a Jeep */

    std::cout << "Jeep" << std::endl;

    director.setBuilder(&jeepBuilder); // using JeepBuilder instance

    car = director.getCar();

    car->specifications();

    std::cout << std::endl;

    /* Build a Nissan */

    std::cout << "Nissan" << std::endl;

    director.setBuilder(&nissanBuilder); // using NissanBuilder instance

    car = director.getCar();

    car->specifications();

    return 0;

感悟：

其实director知道product的组成是什么样的，比如说知道car有body, engine, wheels。但是director不知道是具体是什么body engine wheels。

不过builder知道，利用多态实现不同的产品

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