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Thread: Generics and Wildcards
- 01-30-2009, 11:44 AM #1
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Generics and Wildcards
Hi,
Am trying to understand wildcards (bounded) in java generics. I have method say:
Java Code:public static void someMethod(List <? extends Number> list) { list.add(0, new Integer(9)); //compile error }
- 01-30-2009, 06:31 PM #2
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Found this interesting, since I haven't worked with generics in quite some time, and did a little search. Basically, it's not safe to add an Integer to a list of objects that extend Number because we do not know what ? is. That is, ? is a subtype of Number, but we do not know if it is Rectangle or a supertype of Rectangle.
More info can be found in pages 6-7 in this pdf file:
http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf
Anyways, you should just use List<Number>, as all classes that extend Number can be put into the list anyways.
- 01-30-2009, 11:00 PM #3
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