// package classes;

public class TimeSpan {

	private int hours;
	private int minutes;

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

	// this methods throws an error if invalid hours and minutes 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";
	}

	
		
	public static void main(String[] args) {

		TimeSpan elapsed = new TimeSpan(3, 56);
		

		System.out.println("elapsed time before adding: " + elapsed);
		
		elapsed.add(2, 78);

		System.out.println("elapsed time after adding: " + elapsed);

	}

}

Output:

elapsed time before adding: 3h 56m
elapsed time after adding: 7h 14m