checking class type alternative to instanceof

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Timasmith - 13 Nov 2006 21:56 GMT

Hi,

Can I check if a class is an implementation of an interface by name
without instantiating it?

So I can do this:

if (Class.forName("com.company.package.myclass").newInstance()
instanceof MyInterface) {
// class implements interface
}

but it seems create an instance of it by reflection is suboptimal.

Can I do the same thing without calling newInstance()?

thanks

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Thomas Hawtin - 13 Nov 2006 22:28 GMT

> if (Class.forName("com.company.package.myclass").newInstance()
> instanceof MyInterface) {
[quoted text clipped - 4 lines]
>
> Can I do the same thing without calling newInstance()?

Class.isAssignableFrom

I believe you can also get away without initialising the class with
Class.forName(String,false,ClassLoader).

Tom Hawtin

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Eric Sosman - 13 Nov 2006 22:43 GMT

Timasmith wrote On 11/13/06 16:56,:

> Hi,
>
[quoted text clipped - 11 lines]
>
> Can I do the same thing without calling newInstance()?

You could use getInterfaces() on the Class object and rummage
through the array it returns.

I'm worried about your use of the word "suboptimal," though.
If you're making so many of these inquiries that optimality is
a concern, you're probably making too many. What is it about
the design that requires you to do this so often?

Signature

Eric.Sosman@sun.com

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Timasmith - 13 Nov 2006 22:48 GMT

> You could use getInterfaces() on the Class object and rummage
> through the array it returns.
[quoted text clipped - 6 lines]
> --
> Eric.Sosman@sun.com

It is not so much that I do it so often in the code, I just do it
somewhere which is called a large number of times and I try to avoid
extra object creation where feasible.

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checking class type alternative to instanceof

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