SourceMaking

import java.util.*;

 

class IntSet {

   private Hashtable ht = new Hashtable();

 

   // 1. Design an internal "iterator" class for the "collection" class

   public static class Iterator {

      private IntSet      set;

      private Enumeration e;

      private Integer     current;

      public Iterator( IntSet in ) { set = in; }

      public void    first()       { e = set.ht.keys();  next(); }

      public boolean isDone()      { return current == null; }

      public int     currentItem() { return current.intValue(); }

      public void    next()        {

         try { current = (Integer) e.nextElement(); }

         catch (NoSuchElementException e) { current = null; }

   }  }

 

   public void      add( int in )     { ht.put( new Integer( in ), "null" ); }

   public boolean   isMember( int i ) { return ht.containsKey(new Integer(i)); }

   public Hashtable getHashtable()    { return ht; }

   // 2. Add a createIterator() member to the collection class

   public Iterator  createIterator()  { return new Iterator( this ); }

}

 

class IteratorDemo {

   public static void main( String[] args ) {

      IntSet set = new IntSet();

      for (int i=2; i < 10; i += 2) set.add( i );

      for (int i=1; i < 9; i++)

         System.out.print( i + "-" + set.isMember( i ) + "  " );

 

      // 3. Clients ask the collection object to create many iterator objects

      IntSet.Iterator it1 = set.createIterator();

      IntSet.Iterator it2 = set.createIterator();

 

      // 4. Clients use the first(), isDone(), next(), currentItem() protocol

      System.out.print( "\nIterator:    " );

      for ( it1.first(), it2.first();  ! it1.isDone();  it1.next(), it2.next() )

         System.out.print( it1.currentItem() + " " + it2.currentItem() + "  " );

 

      // Java uses a different collection traversal "idiom" called Enumeration

      System.out.print( "\nEnumeration: " );

      for (Enumeration e = set.getHashtable().keys(); e.hasMoreElements(); )

         System.out.print( e.nextElement() + "  " );

      System.out.println();

}  }