CSC15 Lab 8
			      
			   Due in one week
  
    For this lab you will write a class that will form the
computational part of a program that displays a countdown timer as
demonstrated in class.  The most important function of the class
will involve a nested loop that decrements the timer appropriately.
You will also be writing a class and further practice oop skills.


0.  download the file "timergui.java" from the class homepage. This is
    my part of the program. DO NOT TOUCH THIS FILE AT ALL!  Just make
    sure it's in the same directory as your program.

1.  You are to produce a file called timer.java, with a class timer.
    You will not be writing a main function (that's in my code).

2.  Using the following code as template, define the class.  This
    class needs to have 4 variables (m1,m0,s1,s0) because the
    graphical display shows the time using four separately managed
    digits.  The minute value will consist of digits m1 and m0, with
    m1 ranging from 0 to 5 and m0 ranging from 0 to 9, and similarly
    for s1 and s0.

3.  One of the variables in the timer class you'll define (see skeleton
    below) will be a variable called "gui", which is a link to the graphical
    display component of the program.  This object has two methods you
    can call: void displayUpdate(int m1, int m0, int s1, int s0) and
    void delay(int approx_millesconds) have been predefined.  The first one 
    updates the graphical display with the parameters passed to it.  The
    second one delays by a number of milliseconds.  The exact time is 
    approximate, so you'll NEED TO adjust it so that your timer synchronizes
    with real time.  For example:

      gui.displayUpdate(3,4,2,0); will display 34 minutes and 20 seconds
      gui.delay(1000);   will delay NOT EXACTLY 1000 milliseconds.

   
   See additional instructions in comments below.


4.  After you get the basic count-down timer working, following the 
    instructions and get the reset button to work.


   Sketch the nested loop on paper before coding.


/* 
   Copy the following into a file called timer.java, 
   and follow instructions. 
*/


class timer extends Thread  // a Thread is a concurrently running program.
{
  private int m1, m0, s1, s0;  // minute and second values
  private mywindow gui;      // (link to graphical display in timergui.java)

  // you'll be defining other variables later.

public timer(int a, int b, int c, int d, mywindow g) // constructor
    {
      m1 = a;  m0 = b;  s1 = c;  s0 = d;
      gui = g;
    } // constructor


/* Here is the principal function you'll need to define. Don't change
   the name - it must be called 'run'. It should count down from the
   values the user typed in towards zero using nested loops (4
   levels).  In the body of the innermost loop, you need to call
   displayUpdate and delay after updating the appropriate (s0) value.
   Think carefully and in a structured manner.  figuring out how exactly
   to reset the numbers inside the loops can be tricky and you need to
   also experiment.  Your function should terminate when all 4 values 
   are zero.
*/

public void run()
    {
   
    } // run

// see part II below:
public synchronized void reset()
{
}

} // end class timer


/*
    To run the program, do the following:

    javac timergui.java  
    javac timer.java     
    java timergui


                   PART II : THE RESET BUTTON

   This program actually uses a fairly advanced technique called
multi-threading.  The two parts of the program, the graphical display
and your nested loop, are actually running simultaneously!  This is
why your class "extends Thread".  Without this being the case, you will
not be able to get the reset button to work.  

  To make reset work, you first must define INSIDE the CLASS an
  additional 4 variables that are used to hold the ORIGINAL values of
  the time when the timer object is first created (i.e. when the
  constructor was called).  You then need to modify your constructor
  to set the initial values of these variables to be the same as m1 m0
  s0 s1 (you won't need additional parameters for the constructor -
  think about what you're doing).

  You also need to add the following definition:

  private boolean running.

  And in your constructor function, you need to add the line:
   
     running = false;


  Now, complete the reset function of the timer class:

  public synchronized void reset()
  { 
    // this function should set running to false, set m1, m0, s1 and s0 back
    // to their original values, and call gui.displayUpdate to set the
    // display appropriately.
  }


  Are you done yet?  Not quite!  Your while loop doesn't know when to 
  stop!  You need to modify the run function as follows:
  
     At the very begining of the function, you need to set 

      running = true.

     Then, you need to modify ALL your while loops so that they will
     terminate whenever running is set to false.  That's easy, just
     add the condition while (... && running) to the continuation 
     condition of each of your while loops. 

     If you want, you can look at timergui.java to see how things 
     really work.
*/