Calling a method outside of the main() method

I'm trying to call this method outside of main() in order to assign a variable by chance. The compiler gives "invalid method declaration". How can I get this if statement to run in the class? Thank you for the help.

I have tried to write the if statement directly into the class but then the reference to num in the if statement isn't recognized.

(if(20 <= num))

pseudocode:

public class Class{

    private static int num = numGen(); //random num

    method(num);

    private static void method(int chance){
        if(20 <= chance){
        //stuff happens here
        }
    }
}