Class 36: Implementing Lists with Arrays

/**
 * The start of an implementation of Lists, using arrays
 * as the underlying implementation structure.
 *
 * @author Samuel A. Rebelsky
 * @version 1.1 of November 2000
 */
public class ArrayBasedList
  implements List
{
  /** The elements of the list. */
  // +--------+--------------------------------------------------
  // | Fields |
  // +--------+

  protected Object[] elements;

  /** 
   * The length of the list (different from the length of
   * the array).  Also used as the index of the next element
   * to add.
   */
  protected int length;

  // +--------------+--------------------------------------------
  // | Constructors |
  // +--------------+

  /** Create a new list of specified capacity. */
  public ArrayBasedList(int capacity) {
    this.elements = new Object[capacity];
    this.length = 0;
  } // ArrayBasedSimpleList(int)

  // +---------+-------------------------------------------------
  // | Methods |
  // +---------+

  /** 
   * Add an element to the end of the list.  See the interface for
   * other preconditions and postconditions.
   * Pre: The list has space available for another element. [Unchecked]
   */
  public void addToEnd(Object element) {
    // Add the element.
    this.elements[this.length] = element;
    // Note the increase in length.
    ++this.length;
  } // addToEnd(Object)

  /**
   * Add an element to the end of the list.  See the interface for
   * preconditions and postconditions.
   * Pre: The list has space available for another element. [Unchecked]
   */
  public void addToFront(Object element) {
    // Shift everything to the right one space.
    for(int i = this.length; i > 0; i--) {
      this.elements[i] = this.elements[i-1];
    }
    // Add the new element.
    this.elements[0] = element;
    // Note the increase in length.
    ++this.length;
  } // addToFront(Object)

  /**
   * Delete the first element of the list.
   * See interface for preconditions and postconditions.
   */
  public Object deleteFirst() {
    // Remember the first element.
    Object oldFirst = elements[0];
    // Shift everything left.
    for (int i = 0; i < this.length-1; i++) {
      this.elements[i] = this.elements[i+1];
    }
    // Clear the last element.
    this.elements[this.length] = 0;
    // Note the decrease in length.
    --this.length;
    // Return the deleted thing.
    return oldFirst;
  } // deleteFirst()

  /**
   * Delete the last element of the list.
   * See interface for preconditions and postconditions.
   */
  public Object deleteLast() {
    // Remember the last element.
    Object oldLast = this.elements[this.length];
    // Clear the last element.
    this.elements[this.length] = 0;
    // Note the decrease in length.
    --this.length;
    // Return the deleted element.
    return oldLast;
  } // deleteLast()

  /**
   * Get a new iterator for this list.
   */
  public Iterator getIterator() {
    return new ArrayBasedListIterator(this);
  } // getIterator()

  /**
   * Determine the length of the list.  See the interface
   * for preconditions and postconditions.
   */
  public int length() {
    return this.length;
  } // length()

  /**
   * Determine whether there is space available.  See the
   * interface for preconditions and postconditions.
   */
  public boolean spaceAvailable() {
    // There is space available if the length of the list is
    // less than the length of the array.
    return this.length < this.elements.length;
  } // spaceAvailable()

} // class ArrayBasedList