[biojava-dev] a bit offtopic: javac 1.5 & generics

[Michael Heuer]

Thanks to everyone for the help.  To summarize what I've found,

given

 Set<Foo> foos = new HashSet<Foo>();


this works because foos is already templated

 Set<Foo> unmodifiableFoos = Collections.unmodifiableSet(foos);

the cast here is fine but unnecessary

 Set<Foo> unmodifiableFoos = (Set<Foo>) Collections.unmodifiableSet(foos);

this syntax also works but is unnecessary

 Set<Foo> unmodifiableFoos = Collections.<Foo>unmodifiableSet(foos);


gives an unchecked assignment warning

 Set<Foo> emptyFoos = Collections.EMPTY_SET;

gives an unchecked cast warning

 Set<Foo> emptyFoos = (Set<Foo>) Collections.EMPTY_SET;

illegal expression

 Set<Foo> emptyFoos = Collections.<Foo>EMPTY_SET;

ok

 Set<Foo> emptyFoos = Collections.emptySet();

compile error, found Set<Object> required Set<Foo>

 Set<Foo> emptyFoos = (Set<Foo>) Collections.emptySet();

ok

 Set<Foo> emptyFoos = Collections.<Foo>emptySet();


   michael


On Fri, 6 Feb 2004, Thomas Down wrote:

> Once upon a time, Michael Heuer wrote:
> >
> > Guess I should have read this paper before I began
> >
> > Adding Wildcards to the Java Programming Language
> > > http://www.bracha.org/wildcards.pdf
> >
> >
> > but in short, this works
> >
> >  Set<Foo> foos = new HashSet<Foo>();
> >
> >  Set<Foo> unmodifiableFoos = (Set<Foo>) Collections.unmodifiableSet(foos);
> >
> > and this does not
> >
> >  Set<Foo> emptyFoos = (Set<Foo>) Collections.EMPTY_SET;
>
> No, that doesn't work :-(.
>
> You can, however, do:
>
>    Set<Foo> emptyFoos = Collections.emptySet();
>
> Better than nothing, anyway.
>
>     Thomas.
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