Correct way to prevent instantiation in Java [clos

Question

If we want to prevent instantiation of object in Java we can use several approaches and most obvious of them:

1. abstract keyword
2. private/protected constructor

Let's say class doesn't contain abstract methods and we use abstract keyword to prevent creation of the object. Is this approach incorrect(I mean not syntax correctness, but semantic )? Or it's better to use private constructor in such cases?

Thanks

UPD Class will be a base class for other, though it doesn't contain abstract methods. In my case it some "AbstractTestBase" which contains some common data and utility methods which can be used by some group of integration/unit tests.

Answer 1

As you want to use the class as subclass, the suggestion 'final class with private constructor' will not work obviously, so you'll have to go the 'abstract' way. From the definition of 'abstract class', this is legetimate, as the definition exactly states what you want:

An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.

http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html