Here is the “usual” implementation of this design pattern.
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package pt.joaobrito.builder; /** * This is the main class */ public class BuilderExample { public static void main(String[] args) { Vehicle v1 = new Client(new CarBuilder()).constructVehicle(); System.out.println(v1); Vehicle v2 = new Client(new BikeBuilder()).constructVehicle(); System.out.println(v2); Vehicle v3 = new Client(new CarBuilder()).constructVehicleWithoutWindowsOrSeats(); System.out.println(v3); Vehicle v4 = new Client(new BikeBuilder()).constructVehicleWithoutWindowsOrSeats(); System.out.println(v4); } } /** * The Client class has the responsability of building the vehicles */ class Client { private final VehicleBuilder vehicleBuilder; public Client(VehicleBuilder vehicleBuilder) { this.vehicleBuilder = vehicleBuilder; } /** * Builds a complete vehicle * @return a vehicle */ public Vehicle constructVehicle() { return vehicleBuilder.buildType().buildSeats().buildWindows().get(); } /** * Builds a vehicle without parts * @return a vehicle */ public Vehicle constructVehicleWithoutWindowsOrSeats() { return vehicleBuilder.buildType().get(); } } /** * This class is the abstract builder */ abstract class VehicleBuilder { protected Vehicle vehicle; public VehicleBuilder() { this.vehicle = new Vehicle(); } /** * Vehicle get method * @return the vehicle */ public Vehicle get() { return vehicle; } /** * The 3 following lines are the methods that must be implemented on the concrete builders * @return */ public abstract VehicleBuilder buildType(); public abstract VehicleBuilder buildSeats(); public abstract VehicleBuilder buildWindows(); } /** * This is a concrete builder for Bikes */ class BikeBuilder extends VehicleBuilder { @Override public VehicleBuilder buildType() { vehicle.setType("Bike"); return this; } @Override public VehicleBuilder buildWindows() { vehicle.setWindows(0); return this; } @Override public VehicleBuilder buildSeats() { vehicle.setSeats(2); return this; } } /** * This is the concrete builder for Cars */ class CarBuilder extends VehicleBuilder { @Override public VehicleBuilder buildType() { vehicle.setType("Car"); return this; } @Override public VehicleBuilder buildSeats() { vehicle.setSeats(5); return this; } @Override public VehicleBuilder buildWindows() { vehicle.setWindows(4); return this; } } /** * This is the vehicle class */ class Vehicle { private String type; private int seats; private int windows; public void setType(String type) { this.type = type; } public void setSeats(int seats) { this.seats = seats; } public void setWindows(int windows) { this.windows = windows; } /** * @return a printable vehicle */ @Override public String toString() { return "Vehicle[Type: " + type + "; Seats: " + seats + "; Windows: " + windows + "]"; } } |
The result is:
UML
