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| 11:00 |
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kk joined ##friendlyjava |
| 11:00 |
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kk |
hello |
| 11:00 |
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kk |
i'm learning java |
| 11:01 |
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kk |
want to know when to use nested class |
| 11:34 |
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pulsar |
usually, when you need the nested class not very often and just in the containing class |
| 11:37 |
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pulsar |
for instance event listeners which cant be inlined / anonymized or simple data containers to group a bunch of properties in a nice object with no relevance to the "outside world" |
| 11:52 |
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pdurbin |
I use a nested classed called TestUser within a integration test class. I think of it as a very simplified mock user that has just enough information need for the test to execute: https://github.com/IQSS/dataverse/blob/e6df62a569057411b625ae8ebc250133b12a1193/src/test/java/edu/harvard/iq/dataverse/api/SearchIT.java#L1057 |
| 12:26 |
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kk |
i still dont get it |
| 12:26 |
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kk |
when to use nested class |
| 12:26 |
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kk |
static or non static |
| 12:26 |
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pdurbin |
kk: if you can't think of a reason to use them, don't bother using them. don't worry about it |
| 12:27 |
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kk |
i saw singleton pattern using it |
| 12:28 |
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pdurbin |
kk: can you link to it? |
| 12:29 |
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kk |
okay |
| 12:29 |
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pulsar |
there are some rare situation when you want to access the outer-class "this" pointer inside a nested class. iirc you can only do that when nesting. |
| 12:30 |
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pulsar |
so, class Inner { ..... Outer.this.outersPrivateFieldOrMethod } |
| 12:31 |
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pulsar |
but as pdurbin said, you shoudl not worry about that. 90% of the use cases boil down to personal preference in terms of code / file structure |
| 12:31 |
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kk |
https://en.wikipedia.org/wiki/Singleton_pattern#Initialization-on-demand_holder_idiom |
| 12:31 |
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pulsar |
8% can be omitted as anonymous implementaions will also work |
| 12:31 |
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pulsar |
and 2% would be very obscure |
| 12:35 |
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pulsar |
IMHO that singleton example is rather .... how to put it nicely... syntax / classloader masturbation? |
| 12:37 |
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kk |
Why generics gives problem pulsar |
| 12:37 |
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kk |
i'm using upper bound generics currently |
| 12:37 |
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kk |
<T extends Object> |
| 12:37 |
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pulsar |
gist / pastebin / etc. plz |
| 12:37 |
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kk |
k |
| 12:40 |
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kk |
http://pastebin.com/gYpqg3Ca |
| 12:41 |
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kk |
error >> Type mismatch: cannot convert from Date to T |
| 12:51 |
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kk |
pulsar |
| 12:58 |
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pulsar |
generics are a compile-time construct and the compiler cant detect the return type in your case. |
| 13:00 |
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kk |
why pulsar |
| 13:01 |
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pulsar |
dunno, ask a generics expert ;) most of the time ppl use generics, interfaces would also do |
| 13:01 |
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pulsar |
this is how i feel about generics in java. |
| 13:38 |
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kk |
pdurbin |
| 14:47 |
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pdurbin |
kk: hit 'p' on this slide to see some notes on generics in our code: http://iqss.github.io/javaone2014-bof5619/#31 |
| 14:48 |
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pdurbin |
'submit is a generic method, allowing type-safe execution of any command. If you try to assign the return value of a command to the wrong type you'll get an "incompatible types" error at compile time. The CreateDatasetCommand returns a dataset. The engine prevents you from assigning the result to a DataFile, for example.' |
| 19:15 |
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