Java Example

• builders

  • builders/Builder.java

    package refactoring_guru.builder.example.builders;
    
    import refactoring_guru.builder.example.cars.CarType;
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
     * Builder interface defines all possible ways to configure a product.
    */
    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);
    }

  • builders/CarBuilder.java

    package refactoring_guru.builder.example.builders;
    
    import refactoring_guru.builder.example.cars.Car;
    import refactoring_guru.builder.example.cars.CarType;
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
     * Concrete builders implement steps defined in the common interface.
    */
    public class CarBuilder implements Builder {
        private CarType type;
        private int seats;
        private Engine engine;
        private Transmission transmission;
        private TripComputer tripComputer;
        private GPSNavigator gpsNavigator;
    
        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);
        }
    }

  • builders/CarManualBuilder.java

    package refactoring_guru.builder.example.builders;
    
    import refactoring_guru.builder.example.cars.Manual;
    import refactoring_guru.builder.example.cars.CarType;
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
     * Unlike other creational patterns, Builder can construct unrelated products,
    * which don't have the common interface.
    *
    * In this case we build a user manual for a car, using the same steps as we
    * built a car. This allows to produce manuals for specific car models,
    * configured with different features.
    */
    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);
        }
    }

• cars

  • cars/Car.java

    package refactoring_guru.builder.example.cars;
    
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
     * Car is a product class.
    */
    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;
        }
    }

  • cars/CarType.java

    package refactoring_guru.builder.example.cars;
    
    public enum CarType {
        CITY_CAR, SPORTS_CAR, SUV
    }

  • cars/Manual.java

    package refactoring_guru.builder.example.cars;
    
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
    * Car manual is another product. Note that it does not have the same ancestor
    * as a Car. They are not related.
    */
    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;
        }
    }

• components

  • components/Engine.java

    package refactoring_guru.builder.example.components;
    
    /**
     * Just another feature of a car.
    */
    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;
        }
    }

  • components/GPSNavigator.java

    package refactoring_guru.builder.example.components;
    
    /**
     * Just another feature of a car.
    */
    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;
        }
    }

  • components/Transmission.java

    package refactoring_guru.builder.example.components;
    
    /**
     * Just another feature of a car.
    */
    public enum Transmission {
        SINGLE_SPEED, MANUAL, AUTOMATIC, SEMI_AUTOMATIC
    }

  • components/TripComputer.java

    package refactoring_guru.builder.example.components;
    
    import refactoring_guru.builder.example.cars.Car;
    
    /**
     * Just another feature of a car.
    */
    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");
            }
        }
    }

• director

  • director/Director.java

    package refactoring_guru.builder.example.director;
    
    import refactoring_guru.builder.example.builders.Builder;
    import refactoring_guru.builder.example.cars.CarType;
    import refactoring_guru.builder.example.components.Engine;
    import refactoring_guru.builder.example.components.GPSNavigator;
    import refactoring_guru.builder.example.components.Transmission;
    import refactoring_guru.builder.example.components.TripComputer;
    
    /**
     * Director defines the order of building steps. It works with a builder object
    * through common Builder interface. Therefore it may not know what product is
    * being built.
    */
    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());
        }
    }

• Demo.java

package refactoring_guru.builder.example;

import refactoring_guru.builder.example.builders.CarBuilder;
import refactoring_guru.builder.example.builders.CarManualBuilder;
import refactoring_guru.builder.example.cars.Car;
import refactoring_guru.builder.example.cars.Manual;
import refactoring_guru.builder.example.director.Director;

/**
 * Demo class. Everything comes together here.
 */
public class Demo {

    public static void main(String[] args) {
        Director director = new Director();

        // Director gets the concrete builder object from the client
        // (application code). That's because application knows better which
        // builder to use to get a specific product.
        CarBuilder builder = new CarBuilder();
        director.constructSportsCar(builder);

        // The final product is often retrieved from a builder object, since
        // Director is not aware and not dependent on concrete builders and
        // products.
        Car car = builder.getResult();
        System.out.println("Car built:\n" + car.getCarType());


        CarManualBuilder manualBuilder = new CarManualBuilder();

        // Director may know several building recipes.
        director.constructSportsCar(manualBuilder);
        Manual carManual = manualBuilder.getResult();
        System.out.println("\nCar manual built:\n" + carManual.print());
    }

}

Car built:
SPORTS_CAR

Car manual built:
Type of car: SPORTS_CAR
Count of seats: 2
Engine: volume - 3.0; mileage - 0.0
Transmission: SEMI_AUTOMATIC
Trip Computer: Functional
GPS Navigator: Functional