SimpleTime5.java

public final class SimpleTime5 {
  
   final int hour, minute;

   static final int HOURS_IN_DAY = 24;
   static final int MINUTES_IN_HOUR = 60;
   static final int MINUTES_IN_DAY = HOURS_IN_DAY*MINUTES_IN_HOUR;

   SimpleTime5 (final int h)              { this (h, 0); }
   SimpleTime5 (final int h, final int m) {
      assert 0<=h && h<HOURS_IN_DAY;
      assert 0<=m && m<MINUTES_IN_HOUR;
      this.hour=h; this.minute=m;
   }

   @java.lang.Override
   public String toString () {
      if (hour==0 && minute==0) {
         return ("midnight");
      } else if (hour==12 && minute==0) {
         return ("noon");
      } else {
         return String.format ("%02d:%02d", hour, minute);
      }
   }

   /*
     Design for immutabililty.
   */
   public SimpleTime5 add (final int m) {
      // Wrap around to the next day.
      final int totalMinutes = Math.floorMod (MINUTES_IN_HOUR*hour + minute + m, MINUTES_IN_DAY);
      assert 0<=totalMinutes && totalMinutes<MINUTES_IN_DAY;
      // Integer division truncates
      return new SimpleTime5 (totalMinutes/MINUTES_IN_HOUR, totalMinutes%MINUTES_IN_HOUR);
   }

   public boolean before (final SimpleTime5 t) {
      return ((this.hour < t.hour)
         || ((this.hour == t.hour) && (this.minute < t.minute)));
   }

   public static void main (final String[] args) {
      final SimpleTime5 time = new SimpleTime5 (9, 30);
      final SimpleTime5 ten  = new SimpleTime5 (10);
      System.out.println (time.before(ten));
      System.out.println (time.add(45).add(30));
      System.out.println (time.before(ten));
   }
}