Question

I want to make a convenient super class that will make an instance of whatever subclass it is ran from, without having to hard-code the name of the sub class. What is the fastest way to do this?

We can assume that the subclasses’ constructors will have same signature, e.g. no parameters.

class Main {
    public static void main (String [] args) {
        Main m = new NAME-OF-SUBCLASS();
    }
} 

class MainSub1 extends Main { /*...*/ } 
class MainSub2 extends Main { /*...*/ } 

So when invoking main from MainSub1 ($ java MainSub1 from the command line), a MainSub1 object is created, etc.

As I wrote this, i found this thread where the accepted answer says it can’t be done, but of course it can, somehow, through reflection or something, right?

Answer 1

Not that I’d really recommend it, but there’s a dirty trick to it:

class Main {
    static Main m;
    public static void main (String [] args) {
        // use m
    }
} 

class MainSub1 extends Main { static { m = new MainSub1(); } } 
class MainSub2 extends Main { static { m = new MainSub2(); } }

A serious answer would be to write a separate main for each subclass, but let it call a common inherited method that accepts an appropriate instance.