Builder · 建造者 — Design Patterns

UML 类图

classDiagram class builder { <<interface>> +reset() +setseats(n int) +setengine(engine string) +settripcomputer() +setgps() +getresult() car } class carbuilder { -car car +reset() +setseats(n int) +setengine(engine string) +settripcomputer() +setgps() +getresult() car } class director { <<stateless>> +constructsportscar(builder builder) +constructsuv(builder builder) } class car { +seats int +engine string +tripcomputer boolean +gps boolean +tostring() string } builder <|.. carbuilder director ..> builder carbuilder --> car : builds

director 编排构建步骤，具体 builder 负责创建和返回复杂产品

案例演示

点击 Run 查看汽车构建过程...

          
          
          
          
          
        
/** 建造者接口：定义构建复杂对象的各个步骤 */
public interface Builder {
    void reset();
    void setSeats(int n);
    void setEngine(String engine);
    void setTripComputer();
    void setGPS();
    Car getResult();
}
/** 具体建造者：负责构建 Car 对象 */
public class CarBuilder implements Builder {
    private Car car;

    public void reset() {
        car = new Car();
    }

    public void setSeats(int n) { car.seats = n; }

    public void setEngine(String e) { car.engine = e; }

    public void setTripComputer() { car.tripComputer = true; }

    public void setGPS() { car.gps = true; }

    public Car getResult() { return car; }
}
/** 导演者：控制构建步骤顺序，对客户端隐藏构建细节 */
public class Director {

    /** 构建运动款汽车：2座、运动引擎、含车载电脑和GPS */
    public void constructSportsCar(Builder builder) {
        builder.reset();
        builder.setSeats(2);
        builder.setEngine("Sport Engine");
        builder.setTripComputer();
        builder.setGPS();
    }

    /** 构建 SUV：7座、柴油引擎 */
    public void constructSUV(Builder builder) {
        builder.reset();
        builder.setSeats(7);
        builder.setEngine("Diesel Engine");
        builder.setGPS();
    }
}
/** 复杂产品：汽车 */
public class Car {
    public int seats;
    public String engine;
    public boolean tripComputer;
    public boolean gps;

    public String toString() {
        return "Car{seats=" + seats + ", engine=" + engine
            + ", tripComputer=" + tripComputer + ", gps=" + gps + "}";
    }
}
public class Demo {
    public static void main(String[] args) {
        Director director = new Director();
        CarBuilder builder = new CarBuilder();
        director.constructSportsCar(builder);
        Car car = builder.getResult();
        System.out.println(car.toString());
    }
}

核心要点

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分步骤构建复杂对象

Builder 将对象构建的各个步骤抽象为独立方法，支持中途暂停、参数校验、逐步构建。

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Director 控制构建流程

Director 定义高层构建顺序（如 constructSportsCar），客户端通过 Director 而非直接操作 Builder。

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同一流程，不同表示

CarBuilder 产出 Car，ManualBuilder 实现同一 Builder 接口产出 Manual，Director 复用同一流程。

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建造者 vs. 抽象工厂

抽象工厂产出产品族，建造者分步构建单一复杂对象；建造者更擅长构造有多种可选参数的对象（如 StringBuilder/Lombok @Builder）。