Builder pattern

Today i want to introduce Builder Pattern.

1. First we need to know the Builder Pattern class diagram:
Class diagram:

Now we will explain the meaning of those class:

Builder: An interface used to create complex object.

Concrete Builder: An implementation of Builder. Builder give us the way to construct object. And Concrete Builder show us how to do in detail.

Director: The Director class is responsible for managing the correct sequence of object creation. It receives a Concrete Builder as a parameter and executes the necessary operations on it.

Explanation:
We have a complex object with many part. To create object, we have to create many sub item in it. For example: We have a pizza. There are many type of pizza. Each type has its own way to do pizza.
For Hawaiian pizza: it make from cross, mild, ham+pineapple
For Spicy pizza: it make from pan baked, hot, pepperoni+salami


So we design as below:
+ Builder define how to create pizza. It provide the mean to create pizza:
public void setDough(String dough)
public void setSauce(String sauce)
public void setTopping(String topping)

For each kind of pizza( a concrete builder) , we will give pizza a suitable thing

/** "Product" */
class Pizza
{
    private String dough = "";
    private String sauce = "";
    private String topping = "";
 
    public void setDough(String dough)
    { this.dough = dough; }
    public void setSauce(String sauce)
    { this.sauce = sauce; }
    public void setTopping(String topping)
    { this.topping = topping; }
}

/** "Abstract Builder" */
abstract class PizzaBuilder
{
    protected Pizza pizza;
 
    public Pizza getPizza()
    { 
        return pizza; 
    }
    public void createNewPizzaProduct()
    { 
        pizza = new Pizza(); 
    }
 
    public abstract void buildDough();
    public abstract void buildSauce();
    public abstract void buildTopping();
}
 
/** "ConcreteBuilder" */
class HawaiianPizzaBuilder extends PizzaBuilder
{
    public void buildDough()
    { 
        pizza.setDough("cross"); 
    }
    public void buildSauce()
    { 
        pizza.setSauce("mild"); 
    }
    public void buildTopping()
    { 
        pizza.setTopping("ham+pineapple"); 
    }
}
 
/** "ConcreteBuilder" */
class SpicyPizzaBuilder extends PizzaBuilder
{
    public void buildDough()
    { 
        pizza.setDough("pan baked"); 
    }
    public void buildSauce()
    { 
        pizza.setSauce("hot"); 
    }
    public void buildTopping()
    { 
        pizza.setTopping("pepperoni+salami"); 
    }
}

But we need to describe the sequence to do pizza(step by step)
so we need to implement Director and give it Builder as parameter

class Waiter
{
    private PizzaBuilder pizzaBuilder;
 
    public void setPizzaBuilder(PizzaBuilder pb)
    {
        pizzaBuilder = pb; 
    }
    public Pizza getPizza()
    { 
        return pizzaBuilder.getPizza(); 
    }
 
    public void constructPizza()
    {
        pizzaBuilder.createNewPizzaProduct();
        pizzaBuilder.buildDough();
        pizzaBuilder.buildSauce();
        pizzaBuilder.buildTopping();
    }
}

Finally: We use it:

class BuilderExample
{
    public static void main(String[] args)
    {
        Waiter waiter = new Waiter();
        PizzaBuilder hawaiianPizzaBuilder = new HawaiianPizzaBuilder();
        PizzaBuilder spicyPizzaBuilder = new SpicyPizzaBuilder();
 
        waiter.setPizzaBuilder( hawaiianPizzaBuilder );
        waiter.constructPizza();
 
        Pizza pizza = waiter.getPizza();
    }
}

Hope it can help you to understand builder pattern