SourceMaking

class Stack {                  //    Create an interface/wrapper class that

   protected StackImp imp;     //    "hasa" implementation object and delegates

   public Stack( String s ) {  //    all requsts to it

      if (s.equals("java")) imp = new StackJava();

      else                  imp = new StackMine(); }

   public Stack()                { this( "java" ); }

   public void    push( int in ) { imp.push( new Integer(in) ); }

   public int     pop()          { return ((Integer)imp.pop()).intValue(); }

   public boolean isEmpty()      { return imp.empty(); }

}

 

class StackHanoi extends Stack {   //    Embellish the interface class with

   private int totalRejected = 0;  //     derived classes if desired

   public StackHanoi()           { super( "java" ); }

   public StackHanoi( String s ) { super( s ); }

   public int reportRejected()   { return totalRejected; }

   public void push( int in ) {

      if ( ! imp.empty()  &&  in > ((Integer)imp.peek()).intValue())

         totalRejected++;

      else imp.push( new Integer(in) );

}  }

 

interface StackImp {           //    Create an implementation/body base class

   Object  push( Object o );   Object  peek();

   boolean empty();            Object  pop(); }

 

class StackJava extends java.util.Stack implements StackImp { }

 

class StackMine implements StackImp {        //    Derive the separate impl's

   private Object[] items = new Object[20];  //    from the common abstraction

   private int      total = -1;

   public Object push( Object o ) { return items[++total] = o; }

   public Object peek()           { return items[total]; } 

   public Object pop()            { return items[total--]; }

   public boolean empty()         { return total == -1; }

}

 

class BridgeDemo {

   public static void main( String[] args ) {

      Stack[] stacks = { new Stack("java"), new Stack("mine"), 

         new StackHanoi("java"), new StackHanoi("mine") };

      for (int i=0, num; i < 20; i++) {

         num = (int) (Math.random() * 1000) % 40;

         for (int j=0; j < stacks.length; j++) stacks[j].push( num );

      }

      for (int i=0, num; i < stacks.length; i++) {

         while ( ! stacks[i].isEmpty())

            System.out.print( stacks[i].pop() + "  " );

         System.out.println();

      }

      System.out.println( "total rejected is "

         + ((StackHanoi)stacks[3]).reportRejected() );

}  }