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Java Forum / First Aid / April 2005

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Bounded generics

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Brian - 22 Apr 2005 18:42 GMT
Hi -

I'm trying to extend Vector.  I want it to accept any generic class
that implements a particular interface.

This is my best attempt:

interface MyInterface {
}

class Type1 implements MyInterface {
}

class Type2 implements MyInterface {
}

class MyVector<T implements MyInterface> extends Vector<T> {
}

I want MyVector to accept both Type1 and Type2 as classes but nothing
else which does not implement MyInterface.

I based this code on an O'Reilly book which apparently was written
before 1.5 was released.  I've also tried wildcards without luck.

Thanks in advance.
Daniel Dyer - 22 Apr 2005 19:24 GMT
> Hi -
>
[quoted text clipped - 22 lines]
>
> Thanks in advance.

Try this:

    class MyVector<T extends MyInterface> extends Vector<T> {

You have to use 'extends' rather than 'implements', even with interfaces.  
This one got me the first time too.

Dan.

Signature

Daniel Dyer
http://www.footballpredictions.net

Brian - 22 Apr 2005 21:47 GMT
> Try this:

>     class MyVector<T extends MyInterface> extends Vector<T> {

> You have to use 'extends' rather than 'implements', even with interfaces.  
> This one got me the first time too.

> Dan.

That was it! Thanks Dan.


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