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In software engineering, creational design patterns are design patterns that we’re using in object creation. Creational design patterns solve this problem by somehow controlling this object creation.

Here is the list of creational design patterns:

• Abstract Factory
• Builder
• Factory Method
• Prototype
• Singleton

Now let’s get back to Builder pattern.
here is UML

The intention of Builder Pattern is to abstract steps of construction of object so that different implementations of these steps can construct different representations of objects.
Often, the Builder Pattern is used to build Products in accordance to the Composite pattern, a structure pattern.
Example

public class Director
{
  // Builder uses a complex series of steps
  public void Construct(VehicleBuilder vehicleBuilder)
  {
    vehicleBuilder.BuildFrame();
    vehicleBuilder.BuildEngine();
    vehicleBuilder.BuildWheels();
    vehicleBuilder.BuildDoors();
  }
}

public abstract class VehicleBuilder {
    protected Vehicle vehicle;
    // Property
    public Vehicle getVehicle()
    {
    	return vehicle;
    }

    public abstract void BuildFrame();
    public abstract void BuildEngine();
    public abstract void BuildWheels();
    public abstract void BuildDoors();
}

public class ScooterBuilder extends VehicleBuilder {

	public void BuildFrame()
    {
      vehicle = new Vehicle("Scooter");
      vehicle.AddObject("frame", "Scooter Frame");
    }

    public void BuildEngine()
    {
      vehicle.AddObject("engine", "50 cc");
    }

    public void BuildWheels()
    {
      vehicle.AddObject("wheels", "2");
    }

    public void BuildDoors()
    {
      vehicle.AddObject("doors", "0");
    }
}

public class MotorCycleBuilder extends VehicleBuilder {

	public void BuildFrame()
    {
      vehicle = new Vehicle("MotorCycle");
      vehicle.AddObject("frame", "MotorCycle Frame");
    }

    public void BuildEngine()
    {
      vehicle.AddObject("engine", "500 cc");
    }

    public void BuildWheels()
    {
      vehicle.AddObject("wheels", "2");
    }

    public void BuildDoors()
    {
      vehicle.AddObject("doors", "0");
    }
}

public class CarBuilder extends VehicleBuilder {

	public void BuildFrame()
    {
      vehicle = new Vehicle("Car");
      vehicle.AddObject("frame", "Car Frame");
    }

    public void BuildEngine()
    {
      vehicle.AddObject("engine", "2500 cc");
    }

    public  void BuildWheels()
    {
      vehicle.AddObject("wheels", "4");
    }

    public void BuildDoors()
    {
      vehicle.AddObject("doors", "4");
    }
}

import java.util.*;

//"Product"
public class Vehicle {
	 private String type;
	    private Hashtable parts = new Hashtable();

	    // Constructor
	    public Vehicle(String type)
	    {
	      this.type = type;
	    }

	    public void AddObject(String key, String value)
	    {
	    	parts.put(key, value);
	    }

	    public String GetObject(String key)
	    {
	    	return parts.get(key);
	    }	    

	    public void Show()
	    {
	      System.out.println("\n---------------------------");
	      System.out.println("Vehicle Type: " + type);
	      System.out.println(" Frame : " + parts.get("frame"));
	      System.out.println(" Engine : " + parts.get("engine"));
	      System.out.println(" #Wheels: " + parts.get("wheels"));
	      System.out.println(" #Doors : " + parts.get("doors"));
	    }
}

and for the end, here is the client to show how all of this works together!

public class Client {

    public static void main(String[] args)
    {
      // Create shop with vehicle builders
      Director director = new Director();
      VehicleBuilder b1 = new ScooterBuilder();
      VehicleBuilder b2 = new CarBuilder();
      VehicleBuilder b3 = new MotorCycleBuilder();

      // Construct and display vehicles
      director.Construct(b1);
      b1.getVehicle().Show();

      director.Construct(b2);
      b2.getVehicle().Show();

      director.Construct(b3);
      b3.getVehicle().Show();

    }
}