IRC log for #friendlyjava, 2015-11-07

##friendlyjava on freenode

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Time	S	Nick	Message
00:09			jennyb joined ##friendlyjava
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11:00			kk joined ##friendlyjava
11:00		kk	hello
11:00		kk	i'm learning java
11:01		kk	want to know when to use nested class
11:34		pulsar	usually, when you need the nested class not very often and just in the containing class
11:37		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		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		kk	i still dont get it
12:26		kk	when to use nested class
12:26		kk	static or non static
12:26		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		kk	i saw singleton pattern using it
12:28		pdurbin	kk: can you link to it?
12:29		kk	okay
12:29		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		pulsar	so, class Inner { ..... Outer.this.outersPrivateFieldOrMethod }
12:31		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		kk	https://en.wikipedia.org/wiki/Singleton_pattern#Initialization-on-demand_holder_idiom
12:31		pulsar	8% can be omitted as anonymous implementaions will also work
12:31		pulsar	and 2% would be very obscure
12:35		pulsar	IMHO that singleton example is rather .... how to put it nicely... syntax / classloader masturbation?
12:37		kk	Why generics gives problem pulsar
12:37		kk	i'm using upper bound generics currently
12:37		kk	<T extends Object>
12:37		pulsar	gist / pastebin / etc. plz
12:37		kk	k
12:40		kk	http://pastebin.com/gYpqg3Ca
12:41		kk	error >> Type mismatch: cannot convert from Date to T
12:51		kk	pulsar
12:58		pulsar	generics are a compile-time construct and the compiler cant detect the return type in your case.
13:00		kk	why pulsar
13:01		pulsar	dunno, ask a generics expert ;) most of the time ppl use generics, interfaces would also do
13:01		pulsar	this is how i feel about generics in java.
13:38		kk	pdurbin
14:47		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		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.'
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