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Generics and polymorphism in K&B book

 
Greenhorn
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Although I think I've got a reasonable understanding of generics and polymorphism, one thing I don't understand is - why is


allowed when the K&B book says

"The type of the variable declaration must match the type you pass to the actual object type. If you declare List<Foo> foo then whatever you assign to the foo reference MUST be of the generic type <Foo>. Not a subtype of <Foo>. Not a supertype of <Foo>. Just <Foo>"

(ch 7. p.608)

The example above is not "Just <Integer" - it's <?> which is different from <Integer> as far as I can see.

Any explanation gratefully received.
 
Rancher
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Using the wildcard (<?>) you are asking the compiler to relax the rule(check) you quoted from the book. Essentially, with that statement, you are saying: "x" is a list of(or that can hold) any data type and so the assignment is valid.

You wont be allowed to add to this list though.
 
matt freake
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Thanks - that makes sense to me.

Cheers
 
Monu Tripathi
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you're welcome.
 
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