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Post what you have so far (with the main method) as an SSCCE

You need a main method application entry point, which you don't seem to have.

public class MyClass{
public static void main(String[] args){

}
}


Back to the basics:

Have you defined an application entry point (main method)? If so the launch configuration needs to know about it (if you have a class which contains main open it should automatically do this for you)

What error? It often helps to post the message in their entirety. From what it looks like, I'm guessing its something like uncaught exception - as the last few lines can throw an IOException. See...