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);}@OverrideBuilder setChicken() {kfc.setChicken("鸡腿");return this; // 返回自己，可以链式调用}@OverrideBuilder setCola() {kfc.setCola("可乐");return this;}@OverrideBuilder setPizza() {kfc.setPizza("披萨");return this;}@OverrideKFC 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();}
}