Builder Design Pattern

Nishan Pantha — Sun, 28 May 2017 15:20:24 +0000

Main Points

use builder design pattern when the constructor is very much populated by arguments.
it becomes tedious for creating new instances of a class if constructor is accepting so much arguments.

example

constructor over population

public class Burger {
    private int size;

    private boolean cheese = false;
    private boolean tomato = false;
    private boolean lettuce = false;
    private boolean pepperoni = false;

    public Burger(int size, boolean cheese, boolean tomato, boolean lettuce, boolean pepperoni) {
        this.size = size;
        this.cheese = cheese;
        this.tomato = tomato;
        this.lettuce = lettuce;
        this.pepperoni = pepperoni;
    }
}

Burger burger = new Burger(14, true, true, false, false);

As it can be seen, as the number of items to be added to the burger grows, we have to increase the number of arguments in the constructor too.

This is a very bad design practice because it becomes difficult to remember the order of arguments as well as what type of arguments are there in the arguments.

builder pattern

public class Burger {
    private int size;

    private boolean cheese = false;
    private boolean pepperoni = false;
    private boolean lettuce = false;
    private boolean tomato = false;

    public Burger(BurgerBuilder builder) {
        this.size = builder.size;
        this.cheese = builder.cheese;
        this.pepperoni = builder.pepperoni;
        this.lettuce = builder.lettuce;
        this.tomato = builder.tomato;
    }
}

public class BurgerBuilder {
    public int size;

    public boolean cheese = false;
    public boolean pepperoni = false;
    public boolean lettuce = false;
    public boolean tomato = false;

    public BurgerBuilder(int size) {
        this.size = size;
    }

    public BurgerBuilder addPepperoni() {
        this.pepperoni = true;
        return this;
    }

    public BurgerBuilder addLettuce() {
        this.lettuce = true;
        return this;
    }

    public BurgerBuilder addCheese() {
        this.cheese = true;
        return this;
    }

    public BurgerBuilder addTomato() {
        this.tomato = true;
        return this;
    }

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


Burger burger = (new BurgerBuilder(14))
                    .addPepperoni()
                    .addLettuce()
                    .addTomato()
                    .build();

In the BurgerBuilder class, all the add method returns the builder type so that we can form the chain for subsequent addition.

Finally, build method returns the Burger which is what we want.

Make sure you implement this design pattern according to the context otherwise it will be an overkill. :D

Forem: Nishan Pantha

Builder Design Pattern

Main Points

example