Why a class containg a main method doesn't need to be public in Java? [duplicate]

Answer 1

Here's a similar question with quite a straightforward answer.

Basically, the JVM can access the main in any class that is either of default access or of public access because it is the entry point. If the class is private or protected you will get a compile error.

Answer 2

I don't think the specification says that the class has to be Public. Refer to the examples on the official java tutorial. None of the classes with main method in the examples are declared as Public.

This was discussed previously on stackoverflow. Refer: Package-private class within a .java file - why is it accessible? Explains it well.

Answer 3

Just for kicks, a demo that private classes can also hold main:

class Outer {
    private static class Inner {
        public static void main(String[] args) {
            System.out.println("Hello from Inner!");
        }
    }
}

Compiles and runs fine from the command line:

C:\junk>javac Outer.java
C:\junk>java Outer$Inner
Hello from Inner!

C:\junk>

Answer 4

Mind that main is an early language feature. My guess is that it was thought that a private method could disappear in the .class file, maybe inlined, maybe given a shorter name. So it is a simple overrestricting (?) convention for retrieval of the correct method:

static void main(String[])

Answer 5

if JVM spec mandates that main method should be public since "it can't see main otherwise"

It can see but it doesn't see it as the entry point and that is why it gives NoSuchMethodError: main if you try to execute a class having no such method.

By classic design, the main entry point-

1. Must be named main
2. Must be public
3. Must be static
4. Must be void
5. Must have one argument that is an array of string

Hence,

public static void main(String args[])

Being static, JVM can call it without creating any instance of class which contains the main method. Not sure if it is the main reason for main being static by design.

A class with default access like Hello in your example is only visible to other classes in the same package.

Answer 6

the default access specifier is package.Classes can access the members of other classes in the same package.but outside the package it appears as private but JVM has access to all the classes thus JVM can alter the visibility just to find the beginning of the program thus it makes it default by default