jtulach@368: package org.apidesign.cloneproblem;
jtulach@368: 
jtulach@368: import java.util.Date;
jtulach@368: 
jtulach@368: // BEGIN: interval.api
jtulach@368: /** Quiz: Anyone can come up with a JUnit test to generate
jtulach@368:  * {@link NullPointerException} directly from the code of 
jtulach@368:  * the <code>Interval</code> class?
jtulach@368:  *
jtulach@368:  * @author Jaroslav Tulach <jaroslav.tulach@apidesign.org>
jtulach@368:  */
jtulach@368: public final class Interval {
jtulach@368:     private final Date from, to;
jtulach@368:     
jtulach@368:     /** Constructs interval between two dates.
jtulach@368:      * 
jtulach@368:      * @param from the 'sooner' date
jtulach@368:      * @param to the 'later' date
jtulach@369:      * @throws IllegalArgumentException 
jtulach@369:      *      if <code>from</code> is not less then <code>to</code>
jtulach@368:      */
jtulach@368:     public Interval(Date from, Date to) {
jtulach@368:         if (from == null) {
jtulach@368:             throw new IllegalArgumentException("'from' cannot be null!");
jtulach@368:         }
jtulach@368:         if (to == null) {
jtulach@368:             throw new IllegalArgumentException("'to' cannot be null!");
jtulach@368:         }
jtulach@368:         // shield us from Date's mutability
jtulach@368:         this.from = (Date) from.clone();
jtulach@368:         this.to = (Date)to.clone();
jtulach@368:         if (from.compareTo(to) >= 0) {
jtulach@369:             throw new IllegalArgumentException(
jtulach@369:                 "'from' must be lower than 'to'!"
jtulach@369:             );
jtulach@368:         }
jtulach@368:     }
jtulach@368:     
jtulach@368:     /** The length of the interval in milliseconds 
jtulach@368:      * 
jtulach@368:      * @return amount of milliseconds between 'from' and 'to' dates.
jtulach@368:      */
jtulach@368:     public long getLength() {
jtulach@368:         return to.getTime() - from.getTime();
jtulach@368:     }
jtulach@368: }
jtulach@368: // END: interval.api