Can the class containing `main` be private?

#java #help #watercooler

I realize, that, in some cases, main shall not be private (and sometimes not protected), and in other cases, it may compile.

But, I was wondering if the class containing main can look like this:

private final class Main {
    public static void main(String[] args) { /* ... */ }
}

Top comments (12)

Stefan Drl • Nov 23 '20

Hi! I'm not an expert, but I've never seen a private Main class. In my experience it is always 'public static void main'. Also, I've found this short and logic explanation.

linehammer • Nov 23 '21

In Java, each application must have the main method. The main method is the entry point of every java program. The java program searches for the main method while running. This error occurred when the main method is not available. The reason that the compiler don't complain about the public is because it doesn't care about the main method. It doesn't take difference for it if a main exists or not. It's the JVM which need a start point public and static to launch your application.

So you should make your main method as public:

public static void main(String[] args)

The JVM is programmed to look for a specific signature for the main method before executing the program. It finds this signature by looking for a specific series of bytes in the bytecode. That signature only results from compiling a method that is - public static void main. If any of the three modifiers (public, static and void) are omitted the bytecode code will look different and the JVM will not be able to find your main method.

net-informations.com/java/basics/m...

Calin Baenen • Nov 23 '20

Thanks for the recommendation you provided, but, for some reason, when I try to open it, it just closes, as if window.close() was invoked(??).

Stefan Drl • Nov 23 '20

Hmm, works fine for me. Here is the raw link to the source (tutorialspoint.com/can-we-declare-....)

Calin Baenen • Nov 23 '20

Weird. Whenever I click on links to this website, it brings me to the website homepage (index.htm), when I right click, and try to use one of the Open in ... options, it brings me to a smartredirect.de URL, specifically; this one.

Stefan Drl • Nov 23 '20 • Edited

Let me just write it down here for you, there is no that much content.

Yes, we can declare the main method as private in Java.

It compiles successfully without any errors but at the runtime, it says that the main method is not public.

class PrivateMainMethod {
   private static void main(String args[]){
       System.out.println("Welcome to Tutorials Point");
    }
}

The above code is working successfully at compile time but it will throw an error at the runtime.

Output:

Error: Main method not found in class PrivateMainMethod, 
please define the main
method as:
public static void main(String[] args)
or a JavaFX application class must extend j
avafx.application.Application

Calin Baenen • Nov 23 '20

Thank you.

Nishchal Gautam • Nov 23 '20

Yes, you can make it private, but your JRE (runtime) calls YourJar.main() which isn't available and will fail (its like what happens when you try to invoke a private method) I think it should have exact same error message (because main is called on runtime, compiler doesn't complain, because no one is calling that method, yet)

Calin Baenen • Nov 23 '20

Ol, wb the class containing main inside it?

Nishchal Gautam • Nov 23 '20

I'm not sure if I follow,
basically your java vm will simply call your class.main method, and when it finds that it's private or doesn't even exist, then it'll throw up