Builder Pattern

Builder pattern builds a complex object using simple objects and using a step by step approach. This type of design pattern comes under creational pattern as this pattern provides one of the best ways to create an object.

A Builder class builds the final object step by step. This builder is independent of other objects.

House Class

public class House {

    //Primary
    private String roof, wall, kitchen, bathroom, bedroom, livingRoom;

    //Optional
    private String basement, garage, diningRoom;

    public House(HouseBuilder houseBuilder) {
        this.roof = houseBuilder.roof;
        this.wall = houseBuilder.wall;
        this.kitchen = houseBuilder.kitchen;
        this.bathroom = houseBuilder.bathroom;
        this.bedroom = houseBuilder.bedroom;
        this.garage = houseBuilder.garage;
        this.livingRoom = houseBuilder.livingRoom;
        this.diningRoom = houseBuilder.diningRoom;
        this.basement = houseBuilder.basement;
    }

    public String getRoof() {
        return roof;
    }

    public String getWall() {
        return wall;
    }

    public String getKitchen() {
        return kitchen;
    }

    public String getBathroom() {
        return bathroom;
    }

    public String getBedroom() {
        return bedroom;
    }

    public String getGarage() {
        return garage;
    }

    public String getLivingRoom() {
        return livingRoom;
    }

    public String getDiningRoom() {
        return diningRoom;
    }

    public String getBasement() {
        return basement;
    }

    public static class HouseBuilder {
        //Primary
        private String roof, wall, kitchen, bathroom, bedroom, livingRoom;

        //Optional
        private String basement, garage, diningRoom;

        public HouseBuilder(String roof, String wall, String kitchen, String bathroom, String bedroom, String livingRoom) {
            this.roof = roof;
            this.wall = wall;
            this.kitchen = kitchen;
            this.bathroom = bathroom;
            this.bedroom = bedroom;
            this.livingRoom = livingRoom;
        }

        public HouseBuilder addBasement(String basement) {
            this.basement = basement;
            return this;
        }

        public HouseBuilder addGarage(String garage) {
            this.garage = garage;
            return this;
        }

        public HouseBuilder addDiningRoom(String diningRoom) {
            this.diningRoom = diningRoom;
            return this;
        }

        public House build() {
            return new House(this);
        }

    }

}

Main Class

import BuilderPatternTwo.House;

public class Main {
    public static void main(String[] args) {

        //Builder
        House type1 = new House.HouseBuilder("1", "1", "1", "2", "2", "1").build();
        House type2 = new House.HouseBuilder("1", "1", "1", "2", "2", "1").addGarage("1").build();
        House type3 = new House.HouseBuilder("1", "1", "1", "2", "2", "1").addGarage("1").addBasement("1").build();

        System.out.println("Type 1 = " + type1.getBasement());
        System.out.println("Type 2 = " + type2.getBasement());
        System.out.println("Type 3 = " + type3.getBasement());

    }
}

Result

Type 1 = null
Type 2 = null
Type 3 = 1