package scheme;
/**
 * Represents the empty list.
 * Implemented as a singleton, using the singleton pattern.
 *
 * @author Dung X. Nguyen
 * @version 1.0
 * @since 09/10/00
 * @Custom Copyright 2000 -All rights reserved
 */
public class EmptyList extends AList {
    public final static EmptyList Singleton = new EmptyList ();

    private EmptyList() {
        // NOTE: the constructor is private so that no external client can
        // instantiate an EmptyList.
    }

    /**
     * Throws an IllegalArgumentException.
     * @return does not return.
     * @exception IllegalArgumentException.
     */
    public Object getFirst() {
        throw new IllegalArgumentException ("EmptyList.getFirst()");
    }

    /**
     * Throws an IllegalArgumentException
     * @return does not return.
     * @exception IllegalArgumentException.
     */
    public AList getRest() {
        throw new IllegalArgumentException ("EmptyList.getRest()");
    }

    public String toString() {
        return "";
    }

    /**
     * @return 0.
     */
    public int length() {
        return 0;
    }

    /**
     * @return 0.
     */
    public int getLength() {
        return 0;
    }

    /**
     * Returns the accumulated length, since this is the end of the list.
     *
     * @return int >= 0.
     */
    protected int helpGetLength(int acc) {
        return acc;
    }

    /**
     *  Returns Integet.MAX_VALUE representing +infinity.
     */
    public int getMin() {
        return Integer.MAX_VALUE;
    }

    /**
     * Returns the temporary minimum, since this is the end of the list.
     */
    protected int helpGetMin(int tempMin) {
        return tempMin;
    }
}