Timeline for Do wildcards in Java generics restrict or increase flexibility?
Current License: CC BY-SA 3.0
18 events
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| Feb 9, 2015 at 18:10 | history | tweeted | twitter.com/#!/StackProgrammer/status/564848942316539904 | ||
| Feb 8, 2015 at 6:14 | history | edited | InformedA | CC BY-SA 3.0 |
add an answer in the foot note
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| Feb 8, 2015 at 6:04 | history | edited | InformedA | CC BY-SA 3.0 |
added 108 characters in body
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| Feb 8, 2015 at 5:57 | vote | accept | InformedA | ||
| Feb 6, 2015 at 14:23 | answer | added | Doval | timeline score: 7 | |
| Feb 6, 2015 at 4:32 | comment | added | InformedA |
@Doval Just check with JDK, T super E does not even compile.
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| Feb 6, 2015 at 4:19 | comment | added | InformedA |
@Doval please elaborate with an example in a proper answer. I can use T extends E for T super E, and if needed simply E for T super E .
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| Feb 5, 2015 at 15:39 | comment | added | Doval |
Yes, and you can change ? super E for T super E, but not for T extends E. super != extends. That is my point.
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| Feb 5, 2015 at 15:36 | comment | added | InformedA | There is a duality between type parameters and wildcards | |
| Feb 5, 2015 at 15:34 | comment | added | Doval |
I don't see anything in ggovan's answer that's relevant. ? super E stands for any type that's a superclass of E while T extends E stands for a type that's a subclass of E. Let's say E is Number. popAll(List<? super E>) makes sense because it makes sense to put Numbers into a list of Objects. If you change that to <T extends E> ... List<T>, it doesn't make sense to put Numbers into a List<Integer> because the Number you add may not be an Integer at all.
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| Feb 5, 2015 at 15:10 | comment | added | InformedA | @Doval Or you can read the second quoted block in the answer from ggovan | |
| Feb 5, 2015 at 15:07 | comment | added | InformedA | @Doval Try it yourself and see where the idea is from. | |
| Feb 5, 2015 at 14:14 | comment | added | Doval |
"But List<List<?>> is not flexible" you've got it the wrong way around. The more restrictions you put on the implementer, the more freedom you're giving the caller. The fact that the implementer can't make any assumptions about the contents of the inner Lists means the caller can give them any list-of-lists. That aside, I don't know where you're getting this idea that you can substitute ? super E with T extends E.
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| Feb 5, 2015 at 13:35 | answer | added | ggovan | timeline score: 3 | |
| Feb 5, 2015 at 6:01 | comment | added | InformedA |
@Thomas Eding But List<List<?>> is not flexible (cannot insert other than null) as <E extends Object> List<List<E>>. The latter one is equally permissive.
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| Feb 5, 2015 at 5:37 | comment | added | Thomas Eding |
They increase flexibility. They are useful to accept code you cannot accept with normal type parameters in java. Example would be List<List<T>> is not as permissive as List<List<?>>. en.wikipedia.org/wiki/…
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| Feb 5, 2015 at 3:48 | history | edited | Stephen | CC BY-SA 3.0 |
Changed it to a question.
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| Feb 5, 2015 at 3:38 | history | asked | InformedA | CC BY-SA 3.0 |