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Groups > comp.lang.java.programmer > #14045

Re: generics

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On 4/29/2012 4:13 PM, Neil Morris wrote:
> Dear newsgroup
>
> With the following code, what is the difference from one written with
> Bounded Type Parameters? the code has type 'Number' with the 'add'

I'm not sure what you are asking here.  Bounded type parameters place a 
bound on the type.  Can you give an example for us to compare with?

> method using the 'Integer' type. How can I stop a subtype from being
> passed to the 'add' method?

As pointed out, Number is abstract.  You can't usefully restrict the 
programmer from using subclasses of Number.

But even if you do this:

class Test {
   private Number t;
   public void add( Number n ) { t = n; }
...
}

The user can STILL pass a subclass.  Any normal test you do 
("instanceof") will still pass off an Integer as a Number.

If you own the hierarchy, you can restrict subclassing:

final class MyNumber {...

But don't try to restrict the type if someone else owns the hierarchy. 
They have already determined that a class and its subclasses ARE THE 
SAME THING, and you should treat them as such.

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generics Neil Morris <neil.morris4@googlemail.com> - 2012-04-30 00:13 +0100
  Re: generics Arne Vajhøj <arne@vajhoej.dk> - 2012-04-29 19:39 -0400
    Re: generics Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-04-29 16:48 -0700
  Re: generics markspace <-@.> - 2012-04-29 17:48 -0700

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