builder

生成器模式

1 意图

生成器模式是创建性模式，为了解决类与变量的耦合问题

2 问题

当一个类中变量众多，生成的对象所需变量的数量不同。需要的构造方法是杂乱无章的，。

3 解决办法

可以为每个变量单独进行赋予值，并可以将赋值的顺序和流程记录作为单独的方法

4 生成器模式组件

1. 生成器: 接口中声明所需的构造步骤
2. 具体生成器: 包含构造步骤中的变量，提供构造过程中的不同实现。
3. 产品: 最终生成的产品类。
4. 主管：类调用构造步骤的顺序
5. 客户端： 将具体生成器放入主管中，按照指定构造步骤进行构造生成最终的产品对象

5 生成器方法结构

6 实现步骤

1. 设计所有需要的组件
2. 生成器中定义构造方法
3. 定义具体生成器进行实现
4. 主管类构造组装方法
5. 客户端创建主管类创造所需对象

7 实现效果

package com.ichenxing.builder.components;

/**
 * @date 2023/5/16
 * @description 引擎
 */

public class Engine {
    private final double volume;
    private double mileage;
    private boolean started;

    public Engine(double volume, double mileage) {

        this.volume = volume;
        this.mileage = mileage;
    }

    public void on() {
        started = true;
    }

    public void off() {
        started = false;
    }

    public boolean isStarted() {
        return started;
    }

    public void go(double mileage) {
        if (started) {
            this.mileage += mileage;
        } else {
            System.err.println("Cannot go(), you must start engine first!");
        }
    }

    public double getVolume() {
        return volume;
    }

    public double getMileage() {
        return mileage;
    }
}

package com.ichenxing.builder.components;

/**
 * @date 2023/5/16
 * @description GPS定位
 */
public class GPSNavigator {
    private String route;

    public GPSNavigator() {
        this.route = "221b, Baker Street, London  to Scotland Yard, 8-10 Broadway, London";
    }

    public GPSNavigator(String manualRoute) {
        this.route = manualRoute;
    }

    public String getRoute() {
        return route;
    }
}

/**
 * @date 2023/5/16
 * @description
 */
public enum Transmission {
    SINGLE_SPEED, MANUAL, AUTOMATIC, SEMI_AUTOMATIC
}

package com.ichenxing.builder.components;

import com.ichenxing.builder.Car;

/**
 * @date 2023/5/16
 * @description
 */
public class TripComputer {
    private Car car;

    public void setCar(Car car) {
        this.car = car;
    }

    public void showFuelLevel() {
        System.out.println("Fuel level: " + car.getFuel());
    }

    public void showStatus() {
        if (this.car.getEngine().isStarted()) {
            System.out.println("Car is started");
        } else {
            System.out.println("Car isn't started");
        }
    }
}

public interface Builder {
    void setCarType(CarType type);
    void setSeats(int seats);
    void setEngine(Engine engine);
    void setTransmission(Transmission transmission);
    void setTripComputer(TripComputer tripComputer);
    void setGPSNavigator(GPSNavigator gpsNavigator);
}

public class Car {

    private final CarType carType;
    private final int seats;
    private final Engine engine;
    private final Transmission transmission;
    private final TripComputer tripComputer;
    private final GPSNavigator gpsNavigator;
    private double fuel = 0;

    public Car(CarType carType, int seats, Engine engine, Transmission transmission,
               TripComputer tripComputer, GPSNavigator gpsNavigator) {
        this.carType = carType;
        this.seats = seats;
        this.engine = engine;
        this.transmission = transmission;
        this.tripComputer = tripComputer;
        if (this.tripComputer != null) {
            this.tripComputer.setCar(this);
        }
        this.gpsNavigator = gpsNavigator;
    }

    public CarType getCarType() {
        return carType;
    }

    public double getFuel() {
        return fuel;
    }

    public void setFuel(double fuel) {
        this.fuel = fuel;
    }

    public int getSeats() {
        return seats;
    }

    public Engine getEngine() {
        return engine;
    }

    public Transmission getTransmission() {
        return transmission;
    }

    public TripComputer getTripComputer() {
        return tripComputer;
    }

    public GPSNavigator getGpsNavigator() {
        return gpsNavigator;
    }
}

public enum CarType {
    CITY_CAR, SPORTS_CAR, SUV
}

public class Manual {
    private final CarType carType;
    private final int seats;
    private final Engine engine;
    private final Transmission transmission;
    private final TripComputer tripComputer;
    private final GPSNavigator gpsNavigator;

    public Manual(CarType carType, int seats, Engine engine, Transmission transmission,
                  TripComputer tripComputer, GPSNavigator gpsNavigator) {
        this.carType = carType;
        this.seats = seats;
        this.engine = engine;
        this.transmission = transmission;
        this.tripComputer = tripComputer;
        this.gpsNavigator = gpsNavigator;
    }

    public String print() {
        String info = "";
        info += "Type of car: " + carType + "\n";
        info += "Count of seats: " + seats + "\n";
        info += "Engine: volume - " + engine.getVolume() + "; mileage - " + engine.getMileage() + "\n";
        info += "Transmission: " + transmission + "\n";
        if (this.tripComputer != null) {
            info += "Trip Computer: Functional" + "\n";
        } else {
            info += "Trip Computer: N/A" + "\n";
        }
        if (this.gpsNavigator != null) {
            info += "GPS Navigator: Functional" + "\n";
        } else {
            info += "GPS Navigator: N/A" + "\n";
        }
        return info;
    }
}

public class CarBuilder implements Builder{

    private CarType type;
    private int seats;
    private Engine engine;
    private Transmission transmission;
    private TripComputer tripComputer;
    private GPSNavigator gpsNavigator;

    @Override
    public void setCarType(CarType type) {
        this.type = type;
    }

    @Override
    public void setSeats(int seats) {
        this.seats = seats;
    }

    @Override
    public void setEngine(Engine engine) {
        this.engine = engine;
    }

    @Override
    public void setTransmission(Transmission transmission) {
        this.transmission = transmission;
    }

    @Override
    public void setTripComputer(TripComputer tripComputer) {
        this.tripComputer = tripComputer;
    }

    @Override
    public void setGPSNavigator(GPSNavigator gpsNavigator) {
        this.gpsNavigator = gpsNavigator;
    }

    public Car getResult() {
        return new Car(type, seats, engine, transmission, tripComputer, gpsNavigator);
    }
}

public class CarManualBuilder implements Builder{

    private CarType type;
    private int seats;
    private Engine engine;
    private Transmission transmission;
    private TripComputer tripComputer;
    private GPSNavigator gpsNavigator;

    @Override
    public void setCarType(CarType type) {
        this.type = type;
    }

    @Override
    public void setSeats(int seats) {
        this.seats = seats;
    }

    @Override
    public void setEngine(Engine engine) {
        this.engine = engine;
    }

    @Override
    public void setTransmission(Transmission transmission) {
        this.transmission = transmission;
    }

    @Override
    public void setTripComputer(TripComputer tripComputer) {
        this.tripComputer = tripComputer;
    }

    @Override
    public void setGPSNavigator(GPSNavigator gpsNavigator) {
        this.gpsNavigator = gpsNavigator;
    }

    public Manual getResult() {
        return new Manual(type, seats, engine, transmission, tripComputer, gpsNavigator);
    }
}

public class Director {

    public void constructSportsCar(Builder builder) {
        builder.setCarType(CarType.SPORTS_CAR);
        builder.setSeats(2);
        builder.setEngine(new Engine(3.0, 0));
        builder.setTransmission(Transmission.SEMI_AUTOMATIC);
        builder.setTripComputer(new TripComputer());
        builder.setGPSNavigator(new GPSNavigator());
    }

    public void constructCityCar(Builder builder) {
        builder.setCarType(CarType.CITY_CAR);
        builder.setSeats(2);
        builder.setEngine(new Engine(1.2, 0));
        builder.setTransmission(Transmission.AUTOMATIC);
        builder.setTripComputer(new TripComputer());
        builder.setGPSNavigator(new GPSNavigator());
    }

    public void constructSUV(Builder builder) {
        builder.setCarType(CarType.SUV);
        builder.setSeats(4);
        builder.setEngine(new Engine(2.5, 0));
        builder.setTransmission(Transmission.MANUAL);
        builder.setGPSNavigator(new GPSNavigator());
    }
}

public class BuilderMain {

    public static void main(String[] args) {
        CarBuilder carBuilder = new CarBuilder();
        Director director = new Director();
        director.constructCityCar(carBuilder);
        Car car = carBuilder.getResult();
        System.out.println(car.getCarType());

        CarManualBuilder carManualBuilder = new CarManualBuilder();
        Director manualDirector = new Director();
        manualDirector.constructSportsCar(carManualBuilder);
        Manual manual = carManualBuilder.getResult();
        System.out.println(manual.print());
    }
}

生成器模式: https://refactoringguru.cn/design-patterns/builder