Design Patterns Cont. CSE 110 Discussion - Week 9

Transcription

1 Design Patterns Cont. CSE 110 Discussion - Week 9

2 Factory Method - Decouple object creation from implementation details - Allows you to use an object ( product ) without knowing about creation - Often used to implement Frameworks Core Idea - Define an interface for creating an object, but let subclasses decide which class ( concrete product ) to instantiate - Four participants: Creator, ConcreteCreator, Product, ConcreteProduct

3 Factory Method Example abstract class FruitPicker { protected abstract Fruit createfruit(); Creator public void pickfruit() { Fruit fruit = createfruit();... Product public class OrangePicker extends FruitPicker protected Fruit createfruit() { return new Orange(); ConcreteCreator Factory Method ConcreteProduct

4 Factory Method: Question (Take 7 mins) Apply the Factory Method to clean up the Pizza Store class below. Hint: NY and Chicago should be different types of stores. public class PizzaStore { public Pizza createpizza(string style) { Pizza pizza = null; if (style.equals( NY )) { pizza = new NYStylePizza(); else if (style.equals( Chicago )) { pizza = new ChicagoStylePizza(); return pizza; public Pizza orderpizza(string style) { Pizza pizza = createpizza( NY );...

5 Factory Method: Answer abstract class PizzaStore { protected abstract Pizza createpizza(); public void orderpizza() { Pizza pizza = createpizza();... public class NYPizzaStore extends PizzaStore protected Fruit createpizza() { return new new NYStylePizza();

6 Adapter - When you have two things that are incompatible, what do you do? Make an adapter! - Convert the incompatible interface of a class we want to use into another interface that works for our class Core Idea - We have a Client class that understands how to use a Target interface - The client wants to use a class that is incompatible (the Adaptee) - Bridge the two with an Adapter class - Implements the target interface and delegates to the adaptee

7 Adapter Example Target Adaptee Client Adapter

8 Adapter: Question (Take 7 mins) Consider that you work for a company called iplayer and you create software for DVRs. Every DVR vendor provides you with a SDK with an API to control their DVR. You need to be able to perform basic functions (play, stop, pause, etc.) on every DVR. How do you solve this problem using an Adapter pattern? Show a target interface and your Adapter for a sample vendor below. public class MotorolaVIP1200 { public void beginplayback(long starttime); public long pausevideo();

9 Adapter: Answer public interface IDVRController { public void play(datetime starttime); public DateTime pause(); public class MotorolaVIP1200Adapter implements IDVRController { MotorolaVIP1200 dvr; public MotorolaVIP1200Adapter(MotorolaVIP1200 dvr) { this.dvr = dvr; public void play(datetime starttime) { dvr.beginplayback(starttime.getmillis()); public DateTime pause(datetime starttime) { return new Date(dvr.pauseVideo());

10 Facade Intent: 1. Provide a unified interface to a set of interfaces in a subsystem. 2. Wrap a complicated subsystem with a simpler interface. Advantages: 1. This reduces the learning curve necessary to successfully leverage the subsystem. 2. It also promotes decoupling the subsystem from its potentially many clients. When? A segment of the client community needs a simplified interface to the overall functionality of a complex subsystem.

11 Facade Example SubsystemOne and SubsystemThree do not interact with the internal components of SubsystemTwo. They use the SubsystemTwoWrapper "facade" (i.e. the higher level abstraction).

12 Facade: Question (Take 5 mins) We want to create a Shape and these shapes can be of different kinds like Circle, Rectangle, Square, etc. The objective is to have a ShapeMaker which will use the concrete classes to delegate the user calls of creating a particular kind of shape. The user only knows about the high level interface of calling the ShapeMaker to create a desired kind of shape. Draw the UML diagram with code/pseudocode to depict your design.

13 Facade: Answer (UML)

14 Facade: Answer (Code) public interface Shape { void draw(); public class Rectangle implements Shape public void draw() { System.out.println("Rectangle::draw()"); // Similarly for Square, Circle or other shapes public class FacadePatternDemo { public static void main(string[] args) { ShapeMaker shapemaker = new ShapeMaker(); shapemaker.drawcircle(); shapemaker.drawrectangle(); shapemaker.drawsquare(); public class ShapeMaker { private Shape circle; private Shape rectangle; private Shape square; public ShapeMaker() { circle = new Circle(); rectangle = new Rectangle(); square = new Square(); public void drawcircle(){ circle.draw(); public void drawrectangle(){ rectangle.draw(); public void drawsquare(){ square.draw();