Clock.java

/* *****************************************************************************
 *  Name:              Ada Lovelace
 *  Coursera User ID:  123456
 *  Last modified:     October 16, 1842
 **************************************************************************** */

public class Clock {
    private int hour, min;

    // Creates a clock whose initial time is h hours and m minutes.
    public Clock(int h, int m) {
        if (h < 0 || h > 23)
            throw new IllegalArgumentException("hour must be between 0 and 23");
        if (m < 0 || m > 59)
            throw new IllegalArgumentException("min must be between 0 and 59");
        hour = h;
        min = m;
    }

    // Creates a clock whose initial time is specified as a string, using the format HH:MM.
    public Clock(String s) {
        int indexOfcolon = s.indexOf(':');

        if (indexOfcolon != 2)
            throw new IllegalArgumentException("format should be HH:MM ");

        String hr = s.substring(0, indexOfcolon);
        String m = s.substring(indexOfcolon + 1);

        if (m.length() != 2)
            throw new IllegalArgumentException("format should be HH:MM ");

        hour = Integer.parseInt(hr);
        min = Integer.parseInt(m);

        if (hour < 0 || hour > 23)
            throw new IllegalArgumentException("hour must be between 0 and 23");
        if (min < 0 || min > 59)
            throw new IllegalArgumentException("min must be between 0 and 59");
    }

    // Returns a string representation of this clock, using the format HH:MM.
    public String toString() {
        String h = String.valueOf(hour);
        String m = String.valueOf(min);
        if (h.length() == 1) h = "0" + h;
        if (m.length() == 1) m = "0" + m;
        return h + ":" + m;
    }

    // Is the time on this clock earlier than the time on that one?
    public boolean isEarlierThan(Clock that) {
        int t1 = hour * 60 + min;
        int t2 = that.hour * 60 + that.min;
        if (t2 > t1) return true;
        return false;
    }

    // Adds 1 minute to the time on this clock.
    public void tic() {
        hour = (hour + (min + 1) / 60) % 24;
        min = (min + 1) % 60;
    }

    // Adds Δ minutes to the time on this clock.
    public void toc(int delta) {
        if (delta < 0)
            throw new IllegalArgumentException("delta should be positive");
        hour = (hour + (min + delta) / 60) % 24;
        min = (min + delta) % 60;
    }

    public static void main(String[] args) {
        Clock clock1 = new Clock(2, 59);
        Clock clock2 = new Clock("03:30");
        System.out.println(clock1.isEarlierThan(clock2));
        clock1.tic();
        System.out.println(clock1);
        clock2.toc(50);
        System.out.println(clock2);
    }
}