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Fluent interfaces while trying to make sense of Prototype Pattern

Sometimes I don’t have great opportunities to apply some nice concepts, but I have some time to learn them.

While trying to make some sense of the Prototype Pattern, I was doing some experiments and I needed, of course, the tests to prove my experiments.

It was when coding the tests, trying to define the client interface (not user interface :)), that to my mind came this article from Martin Fowler: Fluent Interface.

Well, what it matters are these two points:

  • Making your tests first helps you, a lot, to define not only the behavior, but also importantly, the client API.
  • Using Fluent Interface with a Builder, it’s a great way to send our message to the objects implementing the API.

Example of using a fluent interface:

package eu.jpereira.trainings.designpatterns.creational.prototype;

import static org.junit.Assert.*;

import java.util.List;
import java.util.Properties;

import org.junit.Test;

import eu.jpereira.trainings.designpatterns.creational.prototype.exception.CannotHaveZeroPartsException;
import eu.jpereira.trainings.designpatterns.creational.prototype.exception.CouldNotCloneLastObjectException;
import eu.jpereira.trainings.designpatterns.creational.prototype.exception.NeedToPackLastVehicleException;
import eu.jpereira.trainings.designpatterns.creational.prototype.exception.VehicleDoesNotHavePartsException;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.Shell;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.Tire;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.Vehicle;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.VehiclePartEnumeration;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.VehiclePartPropertiesEnumeration;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.Window;
/**
 * @author jpereira
 *
 */

public class ClientTest {

	
	/**
	 * Integration Test
	 * @throws CouldNotCloneLastObjectException
	 * @throws CannotHaveZeroPartsException
	 * @throws NeedToPackLastVehicleException
	 * @throws VehicleDoesNotHavePartsException
	 */
	@Test
	public void testCreateBUS() throws CouldNotCloneLastObjectException, CannotHaveZeroPartsException, NeedToPackLastVehicleException, VehicleDoesNotHavePartsException {
		Client client = new Client();
		
		//create a bus car
		//Create props for tire
		Properties tiresProps = new Properties();
		tiresProps.put(VehiclePartPropertiesEnumeration.SIZE,10);

		//Create props for shell
		Properties shellProps = new Properties();
		shellProps.put(VehiclePartPropertiesEnumeration.COLOR,"blue");

		
		Properties windowProps = new Properties();
		windowProps.put(VehiclePartPropertiesEnumeration.WIDTH,20);
		windowProps.put(VehiclePartPropertiesEnumeration.WIDTH,20);

		//client.createVehicle().with(new Tires()).times(4).
		Vehicle vehicle = client.vehicleBuilder().createVehicle().with(new Tire(tiresProps)).times(3).with(new Window(windowProps)).times(8).with(new Shell(shellProps)).times(1).packIt();
		
		//Get all windows
		List<VehiclePart> parts = vehicle.getParts(VehiclePartEnumeration.WINDOW);
		assertEquals(8, parts.size());
		 
	}
}

A hypothetical Builder implementation with a fluent interface:

package eu.jpereira.trainings.designpatterns.creational.prototype;

import java.util.ArrayList;
import java.util.List;

import eu.jpereira.trainings.designpatterns.creational.prototype.exception.CouldNotCloneLastObjectException;
import eu.jpereira.trainings.designpatterns.creational.prototype.exception.CannotHaveZeroPartsException;
import eu.jpereira.trainings.designpatterns.creational.prototype.exception.NeedToPackLastVehicleException;
import eu.jpereira.trainings.designpatterns.creational.prototype.model.Vehicle;

/**
 * @author jpereira
 *
 */
public class SimpleVehicleBuilder implements VehicleBuilder {

	private List<VehiclePart> vehicleParts;
	
	public SimpleVehicleBuilder() {
		this.vehicleParts = createNewPartsBag();
	}
	
	@Override
	public VehicleBuilder createVehicle() throws NeedToPackLastVehicleException{
		//Just check this is allways the first call on the builder
		if (vehicleParts.size()!= 0) {
			throw new NeedToPackLastVehicleException();
		}
		return this;
	}

	
	@Override
	public VehicleBuilder with(VehiclePart part) {
		this.vehicleParts.add(part);
		return this;
	}

	
	@Override
	public VehicleBuilder times(int times) throws CouldNotCloneLastObjectException, CannotHaveZeroPartsException {
		if (times==0) {
			throw new CannotHaveZeroPartsException();
		}
		//get the last one and clone it xtimes 
		if ( this.vehicleParts.size()>0) {
			
			VehiclePart lastObject = this.vehicleParts.get(this.vehicleParts.size()-1);
			//add it xtimes
			for (int i=0; i< times-1; i++) {
				//new object
				try {
					this.vehicleParts.add((VehiclePart)lastObject.clone());
				} catch (CloneNotSupportedException e) {
					//Could not clone it. Wrap exception
					throw new CouldNotCloneLastObjectException(e);
				}
			}
		}
		return this;
		
	}

	
	@Override
	public Vehicle packIt() {
		Vehicle vehicle = new Vehicle(); 
		vehicle.setParts(this.vehicleParts);
		//clear this reference for the chicle parts.
		this.vehicleParts = createNewPartsBag();
		return vehicle;
		
		
	}
	
	//Can be overriden by subclasses
	protected List<VehiclePart> createNewPartsBag() {
		return new ArrayList<VehiclePart>();
	}

}

That’s it



jpereira

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