how to avoid the inheritance to our class without using final keyword?

Question

class a
{
----
}
class b extends a
{

}

But my class a not inherited into b how

Why do you not want to use the `final` keyword? That's specifically what the `final` keyword _does_. — David, Jul 20 '12 at 12:39
@David Yes, it's a bit like asking how to make a field static without using the `static` keyword. It's doable but why? — biziclop, Jul 20 '12 at 12:42
@biziclop: It tangentially reminds me of this question: http://stackoverflow.com/q/4464291/328193 Just an odd use of the language, and makes me think that there's something _behind_ the question that we're not seeing. Like the OP is trying to solve a higher-level problem and needs to step back for a moment to actually solve it, instead of trying to get SO to help with the current attempted "solution." — David, Jul 20 '12 at 12:46
exact duplicate http://stackoverflow.com/questions/451182/stopping-inheritance-without-using-final — Nandkumar Tekale, Jul 20 '12 at 12:51
@David or this was an interview question to test the applicant's knowledge of the programming language. — Jesper, Jul 20 '12 at 12:57
@Jesper: Ah, could be. And interview questions _always_ make me wonder what is the core reason behind it, because they're _always_ contrived and have no core reason :) So many times I've wanted to hear a candidate say, "Why would you even do it that way?" — David, Jul 20 '12 at 13:00

score 9 · Answer 1 · answered Jul 20 '12 at 12:38

9

What exactly is your question? How to prevent class a from being subclassed, but without making class a final?

Make all constructors of class a private. Provide a factory method for creating instances of a.

class a {
    // Private constructor
    private a() {
    }

    // Factory method
    public static a createA() {
        return new a();
    }
}

answered Jul 20 '12 at 12:38

Jesper

its wow .. I've learnt something new today :-) – Maher Abuthraa Apr 30 '14 at 19:41

Nandkumar Tekale · Answer 2 · 2012-07-20T12:44:45.443

2

Use following in your class constructor :

if (this.getClass() != A.class) {
    throw new RuntimeException("Subclassing not allowed");
}

But using this way, you will restrict inheritance at run time.

edited Jul 20 '12 at 12:44

answered Jul 20 '12 at 12:38

Nandkumar Tekale

1

Note though that this isn't a 100% safe method. If someone **really** wants to instantiate a subclass of A, they will be able to. – biziclop Jul 20 '12 at 12:58

2 Answers2