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Other Required Methods

In addition to the required methods for any applet, DragonClock requires other methods to display and update a clock. We will now examine these additional methods. If you remember from lesson 2, these are the first three lines of DragonClock:

The first line says we have an applet instead of an application. The second line gives us access to the Graphics class, and the third line gives us access to the Calendar class. We need the Graphics class because that will paint the clock display. Graphics has one method we will use: paint.

You may wonder why we do not use the Date class to read the current time. Date has been depreciated. Calendar is now the preferred class to use. Calendar has three methods we will use: HOUR_OF_DAY, MINUTE, and SECOND. We will now examine these classes and methods in more detail.

paint()

In paint() we do some initialization, get the current time, and build a string that will display the time. Lets examine the code.

The code will be in red and comments will be in blue. Any commentary will be in regular text.

public void paint(Graphics g)
  {
	/**
	  GRAPHICS method.  This is what paints the clock on the screen.  Uses
	  CALENDAR method for grabbing current time instead of DATE.
	**/
	g.setFont(f);
	d = Calendar.getInstance();
	s = "";
	chour = d.get(Calendar.HOUR_OF_DAY);
	cminute = d.get(Calendar.MINUTE);
	csecond = d.get(Calendar.SECOND);
	AorPM = "AM";

OK, we have defined our font (always a good idea!), created an instance of Calendar, cleared the string that will be our clock display, and finally grabbed the current time. We have a flag to indicate AM or PM which we will initialize to AM.

Now, lets get down to business! Take the current hour and do some tests on it. If the hour is under '10', that is to say one digit, then add a '0' in front of the digit. We want a 12-hour display instead of a 24-hour, so if the hour is over '12' we subtract '12' from the number and set the flag to 'PM'.

About the only manipulation needed for current minutes and seconds is adding a '0' if the number is only one digit.

We want the display to look like this:
hours : minutes : seconds 'AM or PM'
It is a simple matter to add the colon and the AMorPM flag to the string we are building.

	// Get current HOUR
	if (chour < 10)
	{
	  s += "0";
	}
	if (chour > 11)
	{
	  AorPM = "PM";
	}
	if (chour > 12)
	{
	  chour -= 12;
	}
	s += chour + ":";

	// Get current MINUTE
	if (cminute < 10)
	{
	  s += "0";
	}
	s += cminute + ":";

	// Get current SECONDS
	if (csecond < 10)
	{
	  s += "0";
	}
	s += csecond + " " + AorPM;

Now, we are ready to actually draw the clock display. Graphics.drawString is the method we employ. drawString takes three attributes. The first is the string to draw. The second and third are the X and Y offset (in integers) of the beginning of the string.

	g.drawString(s,2,14);
} // end of PAINT method

run()

run() is a method of the Runnable class. All run() does is put the thread to sleep for .2 second to allow the computer to attend to other matters. Sometimes you will want to put error-checking code into your programs. Sometimes you must enter the code. Error checking is required for putting a thread to sleep.

public void run()
  
	/**
	  THREAD method.
	  Basically, we say "If the THREAD is active (Duh, that means the
	  darn thing is working), then put the THREAD to sleep for 200
	  milliseconds and then repaint the screen.
	**/
	while (thread != null)
	{
	  try
	  {
		Thread.sleep(200);
	  }
	  /**
		If there is a problem with putting the THREAD to sleep,
		then we want to CATCH the error code and print it to
		the screen.
	  **/
	  catch (InterruptedException e)
	  {
		String err = e.toString();
		System.out.println(err);
	  }
	  repaint();
	}
	thread = null;
} // end of RUN method

This concludes the examination of the methods used in DragonClock. In the next lesson we will attach the applet to the webpage.

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How to Add Java Applets to Your Site

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