// OpenList.java
// Name:
// Date:
// Comments


/* OpenList is an open linked list that can hold any Java Objects as data
 */
class OpenList
{
  // the data members are private, only
  // to be accessed by the class itself
  private Object first;
  private OpenList rest;

  /**  this is _the_ empty list
    *  there is only one, because it is static*/
  public static OpenList emptyList = new OpenList(null,null);

  /** method: OpenList constructor
    * It is equivalent to a static call to cons */
  public OpenList(Object first, OpenList rest)
  {
    this.first = first;
    this.rest = rest;
  }

  /** method: isEmpty
   *  inputs: none
   *  outputs: true if the calling list is empty; false otherwise
   */
  public boolean isEmpty()
  {
    return first == null && rest == null;
  }

  /** method: isEmpty, static version
   *  inputs: an OpenList, L
   *  outputs: true if the input list is empty; false otherwise
   */
  public static boolean isEmpty(OpenList L)
  {
    return L.isEmpty(); 
  }

  /** method: printItems()
   *  inputs: none
   *  outputs: a String representing the items of this OpenList
   */
  private String printItems()
  {
    if (this.isEmpty())
    {
      return "";
    }
    else if (this.rest.isEmpty())   // handle the case of 1 element
    {
      return this.first.toString(); // so that there is no extra comma
    }
    else
    {
      return "" + this.first + ", " + this.rest.printItems();
    }
  }

  /** method: toString
   *  inputs: none
   *  outputs: a string representing this OpenList
   */
  public String toString()
  {
    String output = "[" + this.printItems() + "]";
    return output;
  }


  /** method: main, the starting point for this class's tests
   *  inputs: a String array not being used right now
   *  outputs: none
   */
  public static void main(String[] args)
  {
    System.out.println("Starting main...");

    /* tests for the constructors
    */
    OpenList greet1 = new OpenList( "Hello", OpenList.emptyList );
    OpenList greet2 = new OpenList( "Hey", greet1 );
    System.out.println(greet1); // should be ["Hello"]
    System.out.println(greet2); // should be ["Hey", "Hello"]

    /* more tests for the constructors
    */
    OpenList numericStrings = OpenList.emptyList;
    System.out.println("numericStrings is " + numericStrings); // should be []
    for (int i=0 ; i<5 ; ++i)
    {
      numericStrings = new OpenList( i , numericStrings );
    }
    System.out.println("numericStrings is " + numericStrings); // should be [4, 3, 2, 1, 0]

    /* Be sure to include tests for all of your methods here !!
    */

    System.out.println("Finishing main...");
  } // end of main

} // end of the OpenList class