How do I go about adding my own method to the class Calendar?

Question

I want to add a method to the class Calendar that will parse a string and set it's date and time with what it parsed from the string. I allready have the parsing code written but I want to know how I can add this to the Calendar class.
I thought I could extend the Calendar class with something like this...
public abstract class myCalendar extends Calendar{
    public myCalendar() {
    public int parseDaytime(String givenLine){
        int flag = 1; //used to report errors
     //do some parsing
        return flag;
}But then in my main program I cannot use any of the Calendar methods...
            myCalendar timeFromServer;
         timeFromServer = timeFromServer.getInstance(); //error, it won't let me use the Calendar methods
            if(timeFromServer.parseDaytime(readFromServer) == 0){
                System.out.println("Error parsing time data from server.");
            }

Answer 1

Aside from my original question, I do not understand why extending Java classes is over kill. You listed the example of extending Thread as a big one. Everytime I create a worker Thread the class I create extends Threads because thats what I learned from every example I have looked at.
Okay. I should be good at writing this by now, so here goes....
You only get to inherit from a superclass once. You can implement as many interfaces as desired. As such, whenever you inherit from a class, you are limiting any other possible inheritance from another superclass. So, all things being equal, you should prefer interfaces to inheritance.
This is why java.lang.Runnable exists. There is almost never a reason to extend Thread. The normal 'is a' test is somewhat misleading in this case when determining whether to extend Thread or not. You may say, "My class is threaded, so I should extend Thread." However, while there exists an 'is a' relationship here, it is not salient. Your class undoubtedly is something else as well. The fact that it is threaded should be thought of as an aspect of feature of your class.
So, in general, you should implement Runnable and not extend Thread.
public class Foo implements Runnable {
   final public void run() {
       // cool asynchronous code goes here
public class FooUser {
   private void someMethod() {
       Thread thread = new Thread(new Foo());
       thread.start();
}- Saish