Help with homework

[GooeyG]

Here is the problem:Change the clock from a 24 hour clock to a 12 hour clock. Be careful: this is not as easy as it might at first seem. In a 12 hour clock the hours after midnight and after noon are not shown as 00:30, but as 12:30. Thus the minute display shown values from 0 to 59, while the hour display shows values from 1 to 12!

The way of how i went to solve this problem was to change the actual parameter in the constructors (24 to 12).Then i modify the setTime() to accommodate the additional features. When hour == 12 implement hour.setValue(00),hour.setValue(30) and call the increment() functions.The problem is that when hour equals 12, the minutes don't display 30. Do i need to call the updateDisplay() within that block?

Thanks!

public class ClockDisplay
{
    private NumberDisplay hours;
    private NumberDisplay minutes;
    private String displayString;    // simulates the actual display
    
    //clockdisplay constuctor
    public ClockDisplay()
    {
        hours = new NumberDisplay(12);
        minutes = new NumberDisplay(60);
        updateDisplay();
    }
    //clockdisplay constuctor
    public ClockDisplay(int hour, int minute)
    {
        hours = new NumberDisplay(12);
        minutes = new NumberDisplay(60);
        setTime(hour, minute);
    }

    /**
     * This method should get called once every minute - it makes
     * the clock display go one minute forward.
     */
    public void timeTick()
    {
        minutes.increment();
        if(minutes.getValue() == 0) {  // it just rolled over!
            hours.increment();
        }
        updateDisplay();
    }

    /**
     * Set the time of the display to the specified hour and
     * minute.
     */
    public void setTime(int hour, int minute)
    {
        hours.setValue(hour);
        minutes.setValue(minute);
        
        //programmer made          
        if (hour >= 12)                    
        {
            hours.setValue(00);
            minutes.setValue(30);
            hours.increment();
            minutes.increment();
        }
        updateDisplay();
    }

    /**
     * Return the current time of this display in the format HH:MM.
     */
    public String getTime()
    {
        return displayString;
    }
    
    /**
     * Update the internal string that represents the display.
     */
    private void updateDisplay()
    {
        //computer made
        displayString = hours.getDisplayValue() + ":" + 
                        minutes.getDisplayValue();     
    }
}