ClockDisplay12

/**
 * The ClockDisplay class implements a digital clock display for a
 * European-style 24 hour clock. The clock shows hours and minutes. The
 * range of the clock is 00:00 (midnight) to 23:59 (one minute before
 * midnight).
 *
 * The clock display receives "ticks" (via the timeTick method) every minute
 * and reacts by incrementing the display. This is done in the usual clock
 * fashion: the hour increments when the minutes roll over to zero.
 *
 * @author Michael Kölling and David J. Barnes
 * @version 2016.02.29
 */
public class ClockDisplay12
{
    public static final String AM = "a.m.";
    public static final String PM = "p.m.";
    private NumberDisplay hours;
    private NumberDisplay minutes;
    private String amOrPm = AM;
    private String displayString;    // simulates the actual display

    /**
     * Constructor for ClockDisplay objects. This constructor
     * creates a new clock set at 00:00.
     */
    public ClockDisplay12()
    {
        hours = new NumberDisplay(12);
        minutes = new NumberDisplay(60);
        updateDisplay();
    }

    /**
     * Constructor for ClockDisplay objects. This constructor
     * creates a new clock set at the time specified by the
     * parameters.
     */
    public ClockDisplay12(int hour, int minute, String amPm)
    {
        hours = new NumberDisplay(12);
        minutes = new NumberDisplay(60);
        setTime(hour, minute, amPm);
    }

    /**
     * This method should get called once every minute - it makes
     * the clock display go one minute forward.
     */
    public void timeTick()
    {
        minutes.increment();
        if(minutes.getValue() == 0) {  // it just rolled over!
            if (hours.getValue() == 0){
                if (amOrPm.equals(AM)){
                    amOrPm = PM;
                }   else {
                    amOrPm = AM;
                }
            }
            hours.increment();
        }
        updateDisplay();
    }


    /**
     * Set the time of the display to the specified hour and
     * minute.
     */
    public void setTime(int hour, int minute, String amPm)
    {
        if (hour == 12)
        {
            hour = 0;
        }
        hours.setValue(hour);
        minutes.setValue(minute);
        if (amPm.equals(ClockDisplay12.AM) || amPm.equals(ClockDisplay12.PM))
        {
            amOrPm = amPm;
            updateDisplay();
            return;
        }
        amOrPm = ClockDisplay12.AM;
        updateDisplay();
        return;
    }

    /**
     * Return the current time of this display in the format HH:MM.
     */
    public String getTime()
    {
        return displayString;
    }

    /**
     * Update the internal string that represents the display.
     */
    private void updateDisplay()
    {
        if (hours.getDisplayValue().equals("00")){
            displayString = "12" + ":" +
                        minutes.getDisplayValue() + amOrPm;
            return;
        }
        displayString = hours.getValue() + ":" +
                        minutes.getDisplayValue() + amOrPm;
    }
}