If it's a normal stand-alone application (not a library or something like that), then you should have a class with a public static void main(String args) method somewhere, which can be used as the starting point of the application.
It's probably better to ask people who know more about the specific project you're trying to use.
I think that you can define a "default" class for the project and that class' main() method is what gets called. Alternately, you can often right-click on a specific class and say to run it, in which case its main() method gets called. This is based on my experiences with Eclipse, I suspect that NetBeans is similar.
Just now verified this behavior in NetBeans 6.9. For the "default" class, look in the Projects Properties, the Run entry, Main Class.
There is a script, on the start of the script it will invoke a java class and after that remaining classes are invoked .
my application contains diffrent classes with main methods.
when i asked my senior, he told me there are different scripts which will initiate different java classes.
same application is used in different scenarios.