// file:    OpenListEnumeration.java
// author:  Robert M. Keller
// purpose: Illustrate implementation of an Enumeration, one for OpenLists

import java.util.*;

/**
 * An OpenListEnumeration is a class implementing the java.util.Enumeration
 * interface.  This allows the creation of Enumeration objects for OpenLists.
 */

class OpenListEnumeration implements java.util.Enumeration
{
/**
 * Error message for NoSuchElementException
 */

String noSuchElement = "No such element in OpenListEnumeration";

/**
 * the remainder of the OpenList being enumerated
 */

private OpenList remainder;


/**
 * Create an OpenListEnumeration for the OpenList.
 * @param theList the OpenList to be enumerated
 */

public OpenListEnumeration(OpenList theList)
  {
  remainder = theList;
  }


/**
 * Indicate whether there are elements remaining in the enumeration.
 * @return true if there are elements remaining, false otherwise
 */

public boolean hasMoreElements()
  {
  return remainder.nonEmpty();
  }


/**
 * Get the next element in the enumeration
 */

public Object nextElement() throws NoSuchElementException
  {
  if( remainder.isEmpty() )
    {
    throw new NoSuchElementException(noSuchElement);
    }

  Object result = remainder.first();
  remainder = remainder.rest();
  return result;
  }

/**
 * Test OpenListEnmeration
 */

public static void main(String arg[])
  {
  OpenList L = OpenList.list("a", "b", "c", "d");

  Enumeration it = new OpenListEnumeration(L);
  
  while( it.hasMoreElements() )
    {
    System.out.println(it.nextElement());
    }

  it = new OpenListEnumeration(L);

  OpenList M = OpenList.solidify(it);

  System.out.println(M);

  System.out.println(it.nextElement());	// Intentionally cause exception
  }
}