运行Java程序的NetBeans，其main为非公共类

Question

I know that there were plenty of questions like this, but in all of them, the answers were " you cannot run a Java program with main method in a non-public class ". ( What if main method is inside "non public class" of java file? )

However, I tried such a situation in NetBeans, and it ran perfectly fine. Why?

Is having a main in a public class a convention or a strict rule ?

Answer 1

The rule is the following

The method main must be declared public , static , and void . It must specify a formal parameter (§8.4.1) whose declared type is array of String .

There is however no restriction on the accessibility of the enclosing class. Note however that top level classes cannot be private or protected . Maybe that's where your confusion arises.

You can very well have

class Example {
    private static class Other {
        public static void main(String[] args) throws Exception {
            System.out.println("main in Other");
        }
    }
}

and execute

> java Example$Other

That would show

main in Other

I don't know why you would , but you can .