package org.apidesign.cloneproblem;

import java.util.Date;

// BEGIN: interval.api

/** Quiz: Anyone can come up with a JUnit test to generate

 * {@link NullPointerException} directly from the code of 

 * the <code>Interval</code> class?

 *

 * @author Jaroslav Tulach <jaroslav.tulach@apidesign.org>

 */

public final class Interval {

    private final Date from, to;

    /** Constructs interval between two dates.

     * 

     * @param from the 'sooner' date

     * @param to the 'later' date

     * @throws IllegalArgumentException if <code>from</code> is not less then <code>to</code>

     */

    public Interval(Date from, Date to) {

        if (from == null) {

            throw new IllegalArgumentException("'from' cannot be null!");

        }

        if (to == null) {

            throw new IllegalArgumentException("'to' cannot be null!");

        }

        // shield us from Date's mutability

        this.from = (Date) from.clone();

        this.to = (Date)to.clone();

        if (from.compareTo(to) >= 0) {

            throw new IllegalArgumentException("'from' must be lower than 'to'!");

        }

    }

    /** The length of the interval in milliseconds 

     * 

     * @return amount of milliseconds between 'from' and 'to' dates.

     */

    public long getLength() {

        return to.getTime() - from.getTime();

    }

}

// END: interval.api