public class ClockDisplay {
   private NumberDisplay hours;
   private NumberDisplay minutes;
   private String displayString;

   public ClockDisplay()
   {
       hours = new NumberDisplay(24);
       minutes = new NumberDisplay(60);
       updateDisplay();

   }

   public ClockDisplay(int hour, int minute)
   {
       hours = new NumberDisplay(24);
       minutes = new NumberDisplay(60);
       setTime(hour, minute);

   }

   public void timeTick()
   {
       minutes.increment();
       if(minutes.getValue() == 0)
       {
           hours.increment();

       }
       updateDisplay();
   }

   public void setTime(int hour, int minute)
   {
       hours.setValue(hour);
       minutes.setValue(minute);
       updateDisplay();
   }

   public String getTime()
   {
       return displayString;
   }

   private void updateDisplay()
   {
       displayString = hours.getDisplayValue() + ":" + minutes.getDisplayValue();
   }

}