Why main() in java is declared as public static void main? What if the main method is declared as private?

Public - main method is called by JVM to run the method which is outside the scope of project therefore the access specifier has to be public to permit call from anywhere outside the application

Static - When the JVM makes are call to the main method there is not object existing for the class being called therefore it has to have static method to allow invocation from class.

Void - Java is platform independent language therefore if it will return some value then the value may mean different to different platforms so unlike C it can not assume a behavior of returning value to the operating system.

Private - If main method is declared as private then - Program will compile properly but at run-time it will give "Main method not public." error.