• Factory pattern example
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Survey of Design Patterns

• Repeating patterns - ``Her garden is like mine, except that in mine I use astilbe.''
• Recurring solutions to design problems you see over and over.
• A set of rules describing how to accomplish certain tasks in the realm of software development.
• Made famous by the text ``Design Patterns'', by Gamma, Helm, et al.
• A list of some of the most well-known design patterns:

  Factory	Abstract Factory
  Singleton	Builder
  Prototype	Adapter
  Bridge	Composite
  Decorator	Facade
  Flyweight	Proxy
  Chain of Responsibility	Command
  Interpreter	Iterator
  Mediator	Memento
  Observer	State
  Strategy	Template
  Visitor

Factory pattern example

• The code and diagram that follow demonstrate a small, simple example of the Factory pattern

  public abstract class Dog {
    public abstract void speak ();
  }
  
  public class Poodle extends Dog {
    public void speak() {
      System.out.println("The poodle says \"arf\"");
    }
  }
  
  public class SiberianHusky extends Dog {
    public void speak() {
      System.out.println("The husky says \"Whazzup?!!\"");
    }
  }
  
  public class Rottweiler extends Dog {
    public void speak() {
      System.out.println("The Rottweiler says (in a very deep voice) \"WOOF!\"");
    }
  }
  

  public class Main {
    public Main() {
      // create a small dog
      Dog dog = DogFactory.getDog("small");
      dog.speak();
  
      // create a big dog
      dog = DogFactory.getDog("big");
      dog.speak();
  
      // create a working dog
      dog = DogFactory.getDog("working");
      dog.speak();
    }
  
    public static void main(String[] args) {
      new Main();
    }
  }
  

  public class DogFactory {
  
    public static Dog getDog(String criteria) {
      if ( criteria.equals("small") )
        return new Poodle();
      else if ( criteria.equals("big") )
        return new Rottweiler();
      else if ( criteria.equals("working") )
        return new SiberianHusky();
  
      return null;
    }
  }
  

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