package inheritance;

public class TimeSpan {

	private int hours;
	private int minutes;

	// Construtor to pass hours and minutes
	public TimeSpan(int hours, int minutes) {
		this.hours = 0;
		this.minutes = 0;
		add(hours, minutes);
	}

	// this methods thorws an error if invalid hours and miutes passes into the
	// argument
	public void add(int hours, int minutes) {
		if (hours < 0 || minutes < 0) {
			throw new IllegalArgumentException();
		}

		this.hours += hours;
		this.minutes += minutes;

		// converts each 60 minutes into one hour
		this.hours += this.minutes / 60;
		this.minutes = this.minutes % 60;
	}

	// returns a String for this time span, such as "6h 15m"
	public String toString() {
		return hours + "h " + minutes + "m";
	}

	// this method overrides the equals method in the Object class
	@Override
	public boolean equals(Object obj) {

		if (obj == null) {
			return false;
		}

		if (obj.getClass() != this.getClass()) {
			return false;
		}

		final TimeSpan ts = (TimeSpan) obj;
		if ((Integer.valueOf(this.hours) == null) ? (Integer.valueOf(ts.minutes) != null)
				: !((Integer.valueOf(this.hours)).equals(Integer.valueOf(ts.hours)))) {
			return false;
		}

		if (this.minutes != ts.minutes) {
			return false;
		}

		return true;
	}

    // if we override equals we should override hashcode() method too
	@Override
	public int hashCode() {

      // chose a random prime number for better hash functionality		
		int hash = 31;
		hash = 17 * hash + (Integer.valueOf(this.hours) != null ? Integer.valueOf(this.hours).hashCode() : 0);
		hash = 17 * hash + this.minutes;
		return hash;
	}

	public static void main(String[] args) {

		TimeSpan elapsed = new TimeSpan(3, 56);
		TimeSpan elapsed1 = new TimeSpan(4, 124);
		TimeSpan elapsed2 = new TimeSpan(3, 56);

		System.out.println(elapsed.equals(elapsed2));
		System.out.println(elapsed1.equals(elapsed2));

	}

}

Output:

true
false