/**
 * Represents the empty list.  Uses the Singleton pattern to model the
 * uniqueness of the empty list.
 * @author Dung X. Nguyen
 * @version 1.1
 * @since 01/25/02
 * @Custom Copyright 2002 -All rights reserved
 */
public class EmptyList extends AList {

    /**
     * Singleton pattern.
     */
    public final static EmptyList Singleton = new EmptyList();

    /**
     * Disables public instantiation of EmptyList.
     */
    private EmptyList() {
    }

    /**
     * Throws an IllegalArgumentException.
     * @return does not return.
     * @exception IllegalArgumentException.
     */
    public Object getFirst() {
        throw new IllegalArgumentException ("EmptyList has no first!");
    }

    /**
     * Throws an IllegalArgumentException
     * @return does not return.
     * @exception IllegalArgumentException.
     */
    public AList getRest() {
        throw new IllegalArgumentException ("EmptyList has no rest!");
    }

    /**
     * Computes a String representation of this EmptyList.
     * @return "()".
     */
    public String toString() {
        return "()";
    }

    /**
    * Computes the length of this EmptyList.
    * @return 0
    */
    public int getLength() {
        return 0;
    }

    /**
     * Computes the length of this EmptyList.
     * @return 0.
     */
    public int getLen() {
        return 0;
    }

    /**
     *  The minimum of the Empty list can be thought of as +infinity.
     *  @return Integet.MAX_VALUE representing +infinity.
     */
     public int getMinimum() {
        return Integer.MAX_VALUE;
     }

    /**
     * Returns the accumulated length, since this is the end of the list.
     * @param acc the length of the list preceding this EmptyList.
     * @return acc.
     */
    protected int helpGetLen(int acc) {
        return acc;
    }

    /**
     *  The minimum of the Empty list can be thought of as +infinity.
     *  @return Integet.MAX_VALUE representing +infinity.
     */
    public int getMin() {
        return Integer.MAX_VALUE;
    }

    /**
    * Returns the accumlated minimum, since this is the end of the list.
    * @param accMin the smallest int containing in the list preceding this NEList.
    * @return tempMin.
    */
    protected int helpGetMin(int tempMin) {
        return tempMin;
    }
}