Invoke java class static initialization via VM option

Question

Is there any way to force static initialization of some class B before entering the main() method of class A, without changing class A, using only VM options?

Explain better what you're trying to achieve. There's no VM option for that (what would be the use?) though. — Kayaman, Jan 06 '14 at 14:32
No, there's a reason why you wonder that. Tell us the reason. — Kayaman, Jan 06 '14 at 16:03

score 1 · Answer 1 · answered Jan 06 '14 at 14:36

I'm not aware of any way to do it without code. In code it's easy of course.

public class C {
   static {
      // Fetch and throw away an instance of B to make sure it is loaded
      B.getInstance();
   }

   static void main(String[] args) {
      // Do stuff, B is initialized
      A.main(args);
   }
}

In fact you could just do

public class C {
   static void main(String[] args) {
      B.getInstance();
      A.main(args);
   }
}

Your request doesn't make a lot of sense though. Ask a question about the problem you are trying to solve by doing this and you will hopefully get a much more useful answer.

Thanks for reply. I didn't consider the option to use other class so it might be helpful. — FireFry, Jan 06 '14 at 15:22

score 0 · Accepted Answer · answered Jan 06 '14 at 21:36

you could create a class that initializes other classes and then calls the real main method, e.g:

public static void main(String[] args) throws Exception {
    Class<?> mainClass = Class.forName(System.getProperty("mainClass"));

    for (String className : System.getProperty("initClasses").split(";")) {
        Class.forName(className);
    }

    Method main = mainClass.getMethod("main", String[].class);
    main.invoke(null, new Object[] { args });
}

Then you would start the application with that class as the main class and specify the real main class and the classes to be initialized via properties.

Invoke java class static initialization via VM option

2 Answers2