If you remove the static modifier from the standard main() method it becomes an instance method. If you then try to execute class the Java runtime system will fail and report:
Exception in thread "main" java.lang.NoSuchMethodError: main.
If you restore the static modifier and change the return type to int, for example, you get the same error. The runtime system expects a static main() method with the void return type, if you change either of these properties you may create a valid method but it will not be executed by the java command.
