import java.text.SimpleDateFormat;
import java.util.Calendar;

public class Main {
	public static void main(String[] args) {
		// Test
		String text = getTimeString(6, 30);
		System.out.println(text);

		text = getTimeString(18, 30);
		System.out.println(text);
	}

	static String getTimeString(int hour, int minute) {
		Calendar calendar = Calendar.getInstance();
		calendar.set(Calendar.HOUR_OF_DAY, hour);
		calendar.set(Calendar.MINUTE, minute);

		return new SimpleDateFormat("HH:mm").format(calendar.getTime());
	}
}