Adapter in Java

class SquarePeg {                     /*** The OLD ***/

   private double width;

   public SquarePeg( double w )       { width = w; }

   public double getWidth()           { return width; }

   public void   setWidth( double w ) { width = w; }

}

 

class RoundHole {                     /*** The NEW ***/

   private int radius;

   public RoundHole( int r ) {

      radius = r;

      System.out.println( "RoundHole: max SquarePeg is " + r * Math.sqrt(2) );

   }

   public int getRadius() { return radius; }

}

 

//Design a "wrapper" class that can "impedance match" the old to the new

class SquarePegAdapter {

 

   //The adapter/wrapper class "has a" instance of the legacy class

   private SquarePeg sp;

 

   public SquarePegAdapter( double w ) { sp = new SquarePeg( w ); }

 

   //Identify the desired interface

   public void makeFit( RoundHole rh ) {

      //The adapter/wrapper class delegates to the legacy object

      double amount = sp.getWidth() - rh.getRadius() * Math.sqrt(2);

      System.out.println( "reducing SquarePeg " + sp.getWidth() + " by "

         + ((amount < 0) ? 0 : amount) + " amount" );

      if (amount > 0) {

         sp.setWidth( sp.getWidth() - amount );

         System.out.println( "   width is now " + sp.getWidth() );

}  }  }

 

class AdapterDemoSquarePeg {

   public static void main( String[] args ) {

      RoundHole        rh = new RoundHole( 5 );

      SquarePegAdapter spa;

 

      for (int i=6; i < 10; i++) {

         spa = new SquarePegAdapter( (double) i );

         //The client uses (is coupled to) the new interface

         spa.makeFit( rh );

}  }  }