Re: Sorting TimeZone
Wojtek wrote:
Semantics!
The word "semantics" means "meaning", so it isn't trivial.
We work in a precise field. An extra semi-colon can make a world of
difference (brought down a phone system a few years ago).
So yes, the labelling DOES make a difference. Whereas a Book is a Book,
where it is used does change its meaning. So in Map<Book,Date>, Book is
a key and in Comparator<Book>, Book is a Type [sic].
Now I see where your difficulty lies and I'm much more sympathetic to your cause.
In both contexts the type parameter signifies a type. In 'Map <K, V>' there
are two type parameters, indicating the types to which the Map is bound. The
first is the type of the key, and the second is the type of the value.
There is no semantic difference between expressing that as 'Map <K, V>',
'Map <T, U>' or even 'Map <foo, bar>'.
Otherwise the Javadoc author would not have made that distinction.
There is no distinction. The choice of letters in the Javadocs is arbitrary
and designed to help us understand the usage of the two types managed by the
'Map', but regardless a type parameter is a type parameter is a type parameter.
It is used differently. As a key, it must provide its own comparison
methodology. As a type, the Comparator makes the comparison, possibly
using an external conversion such as I18N.
That is not true. Take a look again at the Javadocs for 'TreeMap' to which I
pointed you earlier:
<http://java.sun.com/javase/6/docs/api/java/util/TreeMap.html#TreeMap(java.util.Comparator)>
Note that they describe the comparator type parameter as '<? super K>' - that
is the exact same 'K' as in the 'TreeMap <K, V>' type parameter.
For further understanding, check out the rules for type parameters in the JLS.
--
Lew