Re: Comparable loses its interface powers.
Thomas Pornin wrote:
According to Roedy Green <see_website@mindprod.com.invalid>:
If Comparable were just an ordinary interface you could say things
like this:
Comparable a = "abc";
Comparable b = Double.valueOf ( 10.0d );
Comparable c = Double.valueOf ( 12.9d );
int x = b.compareTo( c );
Well, you can. Try it; it compiles and runs.
The Java compiler grumps a bit because it uses runtime typing.
Comparable.compareTo() throws a ClassCastException on type mismatch;
generics are meant to let the compiler check such things, rather than
issuing a runtime exception at runtime. In your situation, you have to
"know" which instances of Comparable can be compared to each other and
which cannot.
Nevertheless, Java supports dynamic typing and the raw type is not
deprecated in any way. Generics are a handy tools, not a mandatory
regulation.
You can do it generically, too, if you write a helper class or method that
takes the type of the column you want to sort (see the original post), either
at compile time or with a Class<T> run-time type token. You get your type
safety at a cost of a slight increase in verbosity.
You can also declare
Comparable <String> a = "abc";
Comparable <Double> b = Double.valueOf ( 10.0d );
Comparable <Double> c = Double.valueOf ( 12.9d );
int x = b.compareTo( c );
Untried:
public static <T> int compare( Comparable <T> a, Comparable <T> b )
{
return a.compareTo( b );
}
I'm not even sure you can call that more verbose since you add a method but
subtract the variable declarations in the caller.
--
Lew