Why can’t a Generic Type Parameter have a lower bound in Java?

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Basically, its not useful enough.

I think your example points out the only advantage of a lower bound, a feature the FAQ calls Restricted Instantiation:

The bottom line is: all that a ” super ” bound would buy you is the restriction that only supertypes of Number can be used as type arguments. ….

But as the other posts point out, the usefulness of even this feature can be limited.

Due to the nature of polymorphism and specialization, upper bounds are far more useful than lower bounds as described by the FAQ (Access To Non-Static Members and Type Erasure). I suspect the complexity introduced by lower bounds aren’t worth its limited value.

OP: I want to add I think you did show it is useful, just not useful enough. Come up with the irrefutable killer use cases and I’ll back the JSR. 🙂

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