Builder Pattern

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Builder Pattern   Creational Patterns (Java)

• When to use: If your application needs similar, but distinct, object types, then the builder pattern is a good choice.
•  Builder pattern is used to construct a complex object step by step and the final step will return the object .
•  This pattern allows a client object to construct a complex object by specifying only its type and content, being shielded from the details related to the object’s representation. This way the construction process can be used to create different representations. The logic of this process is isolated from the actual steps used in creating the complex object, so the process can be used again to create a different object form the same set of simple objects as the first one.

The builder design pattern delegates the construction of an object to a builder class that, depending on the input, constructs an object on your application’s behalf. The Builder Pattern consists of a Builder, ConcreteBuilder, Director and Product.

• The Director object is responsible for the construction process of the complex object but delegates the actual creation and assembly to the Builder interface.
• The Builder object specifies the interface for creating parts of the complex object.
• The Product represents the complex object that is created by the ConcreteBuilder objects. The Product consists of multiple parts that are created separately by the ConcreteBuilder objects.
• The ConcreteBuilder objects create and assemble the parts that make up the Product through the Builder interface.

A client object creates an instance of the Director object and passes it the appropriate Builder object. The Director object invokes the methods on the Builder object to create and initialize specific parts of the Product object. The Builder receives content from the Director object and adds these to the Product object. The Client object has a reference to the Builder object and retrieves the created Product object from it.

Car.java

 public class Car {

 private String engine;

 private String tires;

 private String exhaust;

 public void setEngine( String engine ) {

 this.engine = engine;

 }

 public void setTires( String tires ) {

 this.tires = tires;

 }

 public void setExhaust( String exhaust ) {

 this.exhaust = exhaust;

 }

}

CarBuilder.java

public abstract class CarBuilder {

 protected Car car;

 public Car getCar() {

 return car;

 }

 public void createNewCar() {

 car = new Car();

 }

 public abstract void buildEngine();

 public abstract void buildTires();

 public abstract void buildExhaust();

}

 FastAndFuriousCarBuilder.java

public class FastAndFuriousCarBuilder extends CarBuilder {

 public void buildEngine() {

 car.setEngine( "Twin Turbo with NOS" );

 }

 public void buildTires() {

 car.setTires( "19 inch low profile racing tires" );

 }

  public void buildExhaust() {

 car.setExhaust( "Deafening!" );

 }

}

EconomyCarBuilder.java

public class EconomyCarBuilder extends CarBuilder {

 public void buildEngine() {

 car.setEngine( "4 cylinder" );

 }

 public void buildTires() {

 car.setTires( "15 inch with plenty of air" );

 }

  public void buildExhaust() {

 car.setExhaust( "Quiet and efficient" );

 }

}

Mechanic.java

public class Mechanic {

 private CarBuilder carBuilder;

 public void setCarBuilder( CarBuilder carBuilder ) {

 this.carBuilder = carBuilder;

 }

  public Car getCar() {

 return carBuilder.getCar();

 }

  public void constructCar() {

 carBuilder.createNewCar();

 carBuilder.buildEngine();

 carBuilder.buildTires();

 carBuilder.buildExhaust();

 }

}

CarExample.java

public class CarExample {

 public static void main( String[] args ) {

 Mechanic mechanic = new Mechanic();

 CarBuilder performanceBuilder = new FastAndFuriousCarBuilder();

 CarBuilder economyBuilder = new EconomyCarBuilder();

 mechanic.setCarBuilder( performanceBuilder );

 mechanic.constructCar();

 Car porsche = mechanic.getCar();

 mechanic.setCarBuilder( economyBuilder );

 mechanic.constructCar();

 Car civic = mechanic.getCar();

 }

}