For my assignment we are suppose to make a clock. We need variables of hours, minutes, and seconds and methods like setHours/getHours, setMinutes/getMinutes, setSeconds/getSeconds. Now the parts of the assignment that I am having trouble on is that we need a addClock() method to make the sum of two clock objects and a tickDown() method which decrements the clock object and a tick() method that increments a Clock object by one second. 
Lastly, the part where I am really confused on is, I need to write a main() method in the Clock class to test the functionality of your objects with a separate Tester class with a main() method.
Here is what I have so far... 
public class Clock {
    private int hr; //store hours
    private int min; //store minutes
    private int sec; //store seconds
    //Default constructor
    public Clock ()
    {
        setClock (0, 0, 0);
    }
    public Clock (int hours, int minutes, int seconds)
    {
        setTimes (hours, minute, seconds);
    }
    public void setClock (int hours, int minutes, int seconds)
    {
        if(0 <= hours && hours < 24) {
            hr = hours;
        } else {
            hr = 0;
        }
        if(0 <= minutes && minutes < 60) {
            min = minutes;
        } else {
            min = 0;
        }
        if(0 <= seconds && seconds < 60) {
            sec = seconds;
        } else {
            sec = 0;
        }
    }
    public int getHours ( )
    {
        return hr;
    }
    public int getMinutes ( )
    {
        return min;
    }
    public int getSeconds ( )
    {
        return sec;
    }
    //Method to increment the time by one second
    //Postcondition: The time is incremented by one second
    //If the before-increment time is 23:59:59, the time
    //is reset to 00:00:00
    public void tickSeconds ( )
    {
        sec++;
        if(sec > 59)
        {
            sec = 0;
            tickMinutes ( ); //increment minutes
        }
    }
    public void tickMinutes()
    {
        min++;
        If (min > 59) {
            min = 0;
            tickHours(); //increment hours
        }
    }
    public void tickHours()
    {
        hr++;
        If (hr > 23)
        hr = 0;
    }
}