//----------------------------------------------------------------------------
// List.java                by Dale/Joyce/Weems                      Chapter 3
//
// Defines all constructs for an array based list that do not depend
// on whether or not the list is sorted
//----------------------------------------------------------------------------

package ch03.genericLists;

public abstract class List
{
  protected Listable[] list;          // Array to hold this list’s elements
  protected int numItems;             // Number of elements in this list
  protected int currentPos;           // Current position for iteration

  public List(int maxItems)
  // Instantiates and returns a reference to an empty list object with room for maxItems elements.
  {	
    numItems = 0;
    list = new Listable[maxItems];
  }

  public boolean isFull()
  // Returns whether this list is full. 
  {
    return (list.length == numItems);
  }

  public int lengthIs()
  // Returns the number of elements in this list. 
  {
    return numItems;
  }

  public abstract boolean isThere (Listable item);
  // Returns true if an element with the same key as item is on this list, otherwise returns false.
  
  public abstract Listable retrieve(Listable item);
  // Returns a copy of the list element with the same key as item

  public abstract void insert (Listable item);
  // Adds a copy of item to this list. 
  
  public abstract void delete (Listable item);
  // Deletes the element with the same key as  item from this list. 
  
  public void reset()
  // Initializes current position for an iteration through this list. 
  {
    currentPos  = 0;
  }

  public Listable getNextItem ()
  // Returns copy of the next element in this list. 
  {
    Listable next = list[currentPos];
    if (currentPos == numItems-1)
      currentPos = 0;
    else
      currentPos++;
    return next.copy();
  }

}