Question

Assume I obtained a Class object by loading a class dynamically using Class.forName("Foo"). Foo is abstract in this case, so I cannot call newInstance() on it. (How) is it possible to declare a concrete subclass of Foo?

Answer 1

You declare it as not abstract e.g.

class Bar extends Foo {
    // implement methods are required.
}

In short, just because you loaded the class dynamically doesn’t mean the rules change 😉

Foo is not available at compile-time

If you don’t have Foo available at compile time, you still need to have a sub-class of this class which is concrete to create it. To do this you have two options.

• find a concrete class and create that. You can use the Reflections library to find such a class.
• generate code and compile it using the Compiler API, or BeanShell.
• generate byte code for the subclass using ObjectWeb’s ASM.

I suspect the first option is what you need because unless there is a subclass provided for you, you still need to generate the code for the abstract methods.