CS 342 - 3/29/16

Design Patterns - Result of research into code re-use

  "Gang of Four" Book
  Design Patterns: Elements of Reusable Object-Oriented Software
  by Erich Gamma, Richard Helm, Ralph Johnson and John Vlisses

    - Describes 23 Design patterns

  Adaptor Design Pattern

     Two sections of code that were developed separately
       that now need to work together.


       Client Class    Adaptor Class       Vendor Class




Assume we have a method that uses the Duck class

     public void   methodX ( Duck d )
       {
          ...
          d.quack();
          ...
          d.fly();
          ...
        }

  //   original code uses the Duck interface
  
  Duck d1  = new MallardDuck();
  methodX (d1);

  // we want to call methodX with a parameter of Turkey
  Turkey t1 = new WildTurkey();
  methodX (t1);    // this would fail  

  // but the following will succeed!!
  Duck td1 = new TurkeyAdaptor ( t1  );
  methodX ( td1 );


  The basics of the Adaptor Design Pattern is the create a
     wrapper class for the "turkey" class

  class TurkeyAdaptor implements Duck
   {
      private Turkey t;

      public TurkeyAdaptor ( Tuckey tparam )
       {
          t = tparam;
       }

      public void quack ()
       {
          t.gobble();  
       }

     public void fly()
       {
         for (int i = 0 ; i < 5 ; i++)
            t.fly();
       }
   }


Singleton - When only one instance of a class is ever created.

 - Often occurs with a GUI
 - Also used with shared data


class Singleton
{
	private static Singleton instance = null;

        private int sharedValue1;
        private int sharedValue2;

	private Singleton()
	{
		...
	}

	public static synchronized Singleton getInstance()
	{
		if (instance == null)
			instance = new Singleton();

		return instance;
	}
	...
	public void doSomething()
	{
		...	
	}
}