The Builder Pattern is a software design pattern. The intention is to separate the construction of a complex object from its representation so that the same construction process can create different representations.

Often, the Builder Pattern is used to build Products in accordance to the Composite pattern, a structure pattern.

Class Diagram

Builder Structure

Builder

Abstract interface for creating objects(product).

Concrete Builder

Provide implementation for Builder. Construct and assemble parts to build the objects.

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.

Product

The complex object under construction.

Useful tips

• Builder focuses on constructing a complex object step by step. Abstract Factory emphasizes a family of product objects (either simple or complex). Builder returns the product as a final step, but as far as the Abstract Factory is concerned, the product gets returned immediately.
• Builder often builds a Composite.
• Often, designs start out using Factory Method (less complicated, more customizable, subclasses proliferate) and evolve toward Abstract Factory, Prototype, or Builder (more flexible, more complex) as the designer discovers where more flexibility is needed.
• Sometimes creational patterns are complementary: Builder can use one of the other patterns to implement which components get built. Abstract Factory, Builder, and Prototype can use Singleton in their implementations.

Examples

Java

/** "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");
	}
}

/** "Director" */
class Cook {
	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();
	}
}

/** A given type of pizza being constructed. */
public class BuilderExample {
	public static void main(String[] args) {
		Cook cook = new Cook();
		PizzaBuilder hawaiianPizzaBuilder = new HawaiianPizzaBuilder();
		PizzaBuilder spicyPizzaBuilder = new SpicyPizzaBuilder();

		cook.setPizzaBuilder(hawaiianPizzaBuilder);
		cook.constructPizza();

		Pizza pizza = cook.getPizza();
	}
}

C#

//Implementation in C#.
class Pizza
{
    string dough;
    string sauce;
    string topping;
    public Pizza() {}
    public void SetDough( string d){ dough = d;}
    public void SetSauce( string s){ sauce = s;}
    public void SetTopping( string t){ topping = t;}
}

//Abstract Builder
abstract class PizzaBuilder
{
    protected Pizza pizza;
    public PizzaBuilder(){}
    public Pizza GetPizza(){ return pizza; }
    public void CreateNewPizza() { pizza = new Pizza(); }

    public abstract void BuildDough();
    public abstract void BuildSauce();
    public abstract void BuildTopping();
}

//Concrete Builder
class HawaiianPizzaBuilder : PizzaBuilder
{
    public override void BuildDough()   { pizza.SetDough("cross"); }
    public override void BuildSauce()   { pizza.SetSauce("mild"); }
    public override void BuildTopping() { pizza.SetTopping("ham+pineapple"); }
}

//Concrete Builder
class SpicyPizzaBuilder : PizzaBuilder
{
    public override void BuildDough()   { pizza.SetDough("pan baked"); }
    public override void BuildSauce()   { pizza.SetSauce("hot"); }
    public override void BuildTopping() { pizza.SetTopping("pepparoni+salami"); }
}

/** "Director" */
class Waiter {
    private PizzaBuilder pizzaBuilder;

    public void SetPizzaBuilder (PizzaBuilder pb) { pizzaBuilder = pb; }
    public Pizza GetPizza() { return pizzaBuilder.GetPizza(); }

    public void ConstructPizza() {
        pizzaBuilder.CreateNewPizza();
        pizzaBuilder.BuildDough();
        pizzaBuilder.BuildSauce();
        pizzaBuilder.BuildTopping();
    }
}

/** A customer ordering a pizza. */
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();
    }
}

C++

Visual Prolog

Product

interface pizza 
   predicates 
      setDough : (string Dough). 
      setSauce : (string Sauce). 
      setTopping : (string Topping). 
end interface pizza 
  
class pizza : pizza 
end class pizza 
  
implement pizza 
   facts 
      dough : string := "". 
      sauce : string := "". 
      topping : string := "". 
   clauses 
      setDough(Dough) :- dough := Dough. 
   clauses 
      setSauce(Sauce) :- sauce := Sauce. 
   clauses 
      setTopping(Topping) :- topping := Topping. 
end implement pizza 
   

Abstract Builder

interface pizzaBuilder 
   predicates 
      getPizza : () -> pizza Pizza. 
      createNewPizzaProduct : (). 
   predicates 
      buildDough : (). 
      buildSauce : (). 
      buildTopping : (). 
end interface pizzaBuilder 
  

Visual Prolog does not support abstract classes, but we can create a support class instead:

interface pizzaBuilderSupport 
   predicates from pizzaBuilder 
      getPizza, createNewPizzaProduct 
end interface pizzaBuilderSupport 
  
class pizzaBuilderSupport : pizzaBuilderSupport 
end class pizzaBuilderSupport 
  
implement pizzaBuilderSupport 
   facts 
      pizza : pizza := erroneous. 
   clauses 
      getPizza() = pizza. 
   clauses 
      createNewPizzaProduct() :- pizza := pizza::new(). 
end implement pizzaBuilderSupport 
  

ConcreteBuilder #1

class hawaiianPizzaBuilder :  pizzaBuilder 
end class hawaiianPizzaBuilder 
  
implement hawaiianPizzaBuilder 
   inherits pizzaBuilderSupport 
  
   clauses 
      buildDough() :- getPizza():setDough("cross"). 
   clauses 
      buildSauce() :- getPizza():setSauce("mild"). 
   clauses 
      buildTopping() :- getPizza():setTopping("ham+pineapple"). 
end implement hawaiianPizzaBuilder 
  

ConcreteBuilder #2

class spicyPizzaBuilder :  pizzaBuilder 
end class spicyPizzaBuilder 
  
implement spicyPizzaBuilder 
   inherits pizzaBuilderSupport 
  
   clauses 
      buildDough() :- getPizza():setDough("pan baked"). 
   clauses 
      buildSauce() :- getPizza():setSauce("hot"). 
   clauses 
      buildTopping() :- getPizza():setTopping("pepperoni+salami"). 
end implement spicyPizzaBuilder 
  

Director

interface waiter 
   predicates 
      setPizzaBuilder : (pizzaBuilder PizzaBuilder). 
      getPizza : () -> pizza Pizza. 
   predicates 
      constructPizza : (). 
end interface waiter 
  
class waiter : waiter 
end class waiter 
  
implement waiter 
   facts 
      pizzaBuilder : pizzaBuilder := erroneous. 
   clauses 
      setPizzaBuilder(PizzaBuilder) :- pizzaBuilder := PizzaBuilder. 
   clauses 
      getPizza() = pizzaBuilder:getPizza(). 
   clauses 
      constructPizza() :- 
         pizzaBuilder:createNewPizzaProduct(), 
         pizzaBuilder:buildDough(), 
         pizzaBuilder:buildSauce(), 
         pizzaBuilder:buildTopping(). 
end implement waiter 
  

A customer ordering a pizza.

goal 
   Hawaiian_pizzabuilder = hawaiianPizzaBuilder::new(), 
   Waiter = waiter::new(), 
   Waiter:setPizzaBuilder(Hawaiian_pizzabuilder), 
   Waiter:constructPizza(), 
   Pizza = Waiter:getPizza().

perl

PHP

/** Product **/
class Pizza{
  private $dough;
  private $sauce;
  private $topping;
  public function setDough($dough){
    $this->dough = $dough;
  }
  public function setSauce($sauce){
    $this->sauce = $sauce;
  }
  public function setTopping($topping){
    $this->topping = $topping;
  }
}

/** Abstract builder **/
abstract class PizzaBuilder{
  protected $pizza;
  public function __construct(){
    $this->pizza = new Pizza();
  }
  public function getPizza(){
    return $this->pizza;
  }
  abstract function buildDough();
  abstract function buildSauce();
  abstract function buildTopping();
}

/** Concrete builder  **/
class SpicyPizza extends PizzaBuilder{
  public function buildDough(){
    $this->pizza->setDough('crispy');
  }
  public function buildSauce(){
    $this->pizza->setSauce('hot');
  }
  public function buildTopping(){
    $this->pizza->setTopping('pepperoni+salami');
  }
}

/** Director **/
class Chef{
  private $pizza_builder;
  public function setPizzaBuilder(PizzaBuilder $pizza_builder){
    $this->pizza_builder = $pizza_builder;
  }
  public function cookPizza(){
    $this->pizza_builder->buildDough();
    $this->pizza_builder->buildSauce();
    $this->pizza_builder->buildTopping();
  }
  public function getPizza(){
    return $this->pizza_builder->getPizza();
  }
}

//Customer orders a Pizza.
$chef = new Chef();

$order = new SpicyPizza();
$chef->setPizzaBuilder($order);
$chef->cookPizza();
$pizza = $chef->getPizza();

print_r($pizza);

External links

• Jt J2EE Pattern Oriented Framework
• What is the difference between Factory pattern and Builder Pattern ?

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