// Represents a time span of hours and minutes elapsed.
// Class invariant: minutes < 60

public class TimeSpan {
	private int minutes;
	
	// Constructs a time span with the given interval
	// Precondition: hours >= 0 and minutes >= 0
	public TimeSpan () {
		minutes = 0;
	}
	
	// Constructs a time span with the given interval
	// Precondition: hours >= 0 and minutes >= 0
	public TimeSpan (int hrs, int min) {
		minutes = 0;
		add(hrs, min);
	}
	
	//-------------------------------
	// Sets the time span to the given interval
	// Precondition: hours >= 0 and minutes >= 0
	public void set(int hrs, int min) {
		minutes = 0;
		add(hrs, min);
	}
	
	//-------------------------------
	// Resets the time span to zero
	public void reset() {
		minutes = 0;
	}
	
	//----------------------------------
	// Add the given interval to the time span
	// Precondition: hours >= 0 and minutes >= 0
	public void add(int hrs, int min) {
		minutes += hrs * 60 + min;
	}
	
	//-----------------------------------
	// Returns whether obj is a TimeSpan representing the same
	// number of hours and minutes as this TimeSpan object
	public boolean equals(Object obj) {
		if (obj instanceof TimeSpan) {
			TimeSpan candidate = (TimeSpan) obj;
			return (minutes == candidate.minutes);
		} else {
			return false;
		}
	}
	
	//---------------------------------------
	// Returns a String for this time span, e.g. "6h15m"
	public String toString() {
		int hours = minutes / 60;
		return hours + "h" + (minutes % 60) + "m";
	}

}