hi all,
this might be of interest to some of you:
http://developer.java.sun.com/developer/earlyAccess/adding_generics/index.html
Sun published version 2.0 of the early access drops for generics. This
release aslo includes:
* concise object array literals (aka varargs)
* jsr 201 - syntactic sugar like enums, autoboxing, static imports,
enhaced for construct.
also the generic impl is enhanced with variance support, and a variance
whitepaper is included.
I just skimmed through the whitepaper, but it sounds interesting. You
can add qualifiers when declare variables of generic type:
(-,+,*,=)
+ .. covariance (read-only situations)
- .. contravariance (write-only situations)
* .. bivariance (don't care about the type) [neither read from nor
write to instances)
= .. invariance (both read and written to)
[ can be obmitted, Set<A> == Set<=A> ]
an example for covariance:
<code>
Set<+Number> aReadOnlySet;
aReadOnlySet = new HashSet<Integer>( );
Iterator<+Number> i = aReadOnlySet.iterator( );
double sum = .0;
while ( i.hasNext( ) ) sum += i.next( ).doubleValue( );
</code>
<+Type> is used only for getting values from, not for setting.
allthough it is not fix, if this feature will ship with j2se 1.5.
at least sounds interesting ...
bye,
-- Jakob
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