建造者设计模式学习

1.介绍

建造者模式是一种创建型设计模式，它将一个复杂对象的构建过程与它的表示分离，使得相同的构建过程可以创建不同的表示。通过分步骤地构建对象，建造者模式提供了更细粒度的控制和灵活性，特别适合需要灵活创建复杂对象的场景。

Builder（建造者接口）：定义创建对象不同部分的抽象接口。
ConcreteBuilder（具体建造者）：实现 Builder 接口，负责构建复杂对象的各个部分，并最终返回完整对象。
Director（指挥者）：指定复杂对象的构建顺序和步骤，协调 Builder 的调用。【指挥者可以简略】
Product（产品）：由多个部件组成的复杂对象，是建造的最终结果。

2.简单例子

标准的例子：

#include <iostream>
#include <string>

// Product: 复杂对象
class Computer {
private:
    std::string CPU;
    std::string GPU;
    std::string RAM;
    std::string Storage;

public:
    void setCPU(const std::string& cpu) { CPU = cpu; }
    void setGPU(const std::string& gpu) { GPU = gpu; }
    void setRAM(const std::string& ram) { RAM = ram; }
    void setStorage(const std::string& storage) { Storage = storage; }

    void show() const {
        std::cout << "Computer Configuration:\n"
                  << "CPU: " << CPU << "\n"
                  << "GPU: " << GPU << "\n"
                  << "RAM: " << RAM << "\n"
                  << "Storage: " << Storage << "\n";
    }
};

// Builder: 抽象建造者
class ComputerBuilder {
public:
    virtual ~ComputerBuilder() = default;
    virtual void buildCPU() = 0;
    virtual void buildGPU() = 0;
    virtual void buildRAM() = 0;
    virtual void buildStorage() = 0;
    virtual Computer* getResult() = 0;
};

// ConcreteBuilder: 具体建造者
class GamingComputerBuilder : public ComputerBuilder {
private:
    Computer* computer;

public:
    GamingComputerBuilder() { computer = new Computer(); }
    ~GamingComputerBuilder() { delete computer; }

    void buildCPU() override { computer->setCPU("Intel i9"); }
    void buildGPU() override { computer->setGPU("NVIDIA RTX 4090"); }
    void buildRAM() override { computer->setRAM("32GB DDR5"); }
    void buildStorage() override { computer->setStorage("2TB SSD"); }

    Computer* getResult() override {
        Computer* result = computer;
        computer = nullptr; // 防止重复释放
        return result;
    }
};

// Director: 指挥者
class Director {
private:
    ComputerBuilder* builder;

public:
    void setBuilder(ComputerBuilder* b) { builder = b; }

    Computer* construct() {
        builder->buildCPU();
        builder->buildGPU();
        builder->buildRAM();
        builder->buildStorage();
        return builder->getResult();
    }
};

// 客户端代码
int main() {
    Director director;
    GamingComputerBuilder gamingBuilder;

    // 设置建造者
    director.setBuilder(&gamingBuilder);

    // 构建计算机
    Computer* gamingComputer = director.construct();

    // 显示结果
    gamingComputer->show();

    delete gamingComputer;
    return 0;
}

// 其实director有点死板，它每次都要使用不同的builder，才能创建不同的对象，直接把创建产品的任务交给builder自己也行。

2.1 链式编程

https://zhuanlan.zhihu.com/p/143101326

关键点是builder的函数直接返回产品对象。

// 产品类
public class KFC {
    //套餐必点
    private String hamburger;
    private String chips;

    //套餐选点
    private String chicken;
    private String cola;
    private String pizza;
    public KFC(String hamburger,String chips){
        this.hamburger = hamburger;
        this.hamburger = chips;
    }
    public void setChicken(String chicken) {
        this.chicken = chicken;
    }

    public void setCola(String cola) {
        this.cola = cola;
    }

    public void setPizza(String pizza) {
        this.pizza = pizza;
    }
};

// 抽象builder
public abstract class Builder {
        abstract Builder setChicken();
        abstract Builder setCola();
        abstract Builder setPizza();
        abstract KFC getKFC();
}

// 具体builder
public class ConcreteBuilder extends Builder {
    KFC kfc;
    public ConcreteBuilder(String hamburger,String chips){
        kfc = new KFC(hamburger,chips);
    }
    @Override
    Builder setChicken() {
        kfc.setChicken("鸡腿");
        return this; // 返回自己，可以链式调用
    }

    @Override
    Builder setCola() {
        kfc.setCola("可乐");
        return this;
    }

    @Override
    Builder setPizza() {
        kfc.setPizza("披萨");
        return this;
    }

    @Override
    KFC getKFC() {
        return kfc;
    }
}

// main函数
public class BTest {
    public static void main(String[] args) {
                // 实例化一个具体的builder类，通过它返回一个具体对象
       KFC kfc = new ConcreteBuilder("汉堡","薯条").setChicken().setCola().getKFC();
    }
}