Re: Java 2.0 Grammar Problems

"Michael Schoettner" <schoettner@informatik.uni-ulm.de> writes:
[...]
>Primary:
> ( Expression )
> this [Arguments]
> super SuperSuffix
> Literal
> new Creator
> Identifier { . Identifier }[ IdentifierSuffix]
> BasicType BracketsOpt .class (*)
> void.class (**)
>
>(*) + (**) What are these productions good for?


They name Class instances that represent the primitive types (int, boolean,
float etcetera) and arrays thereof, and also void. These are used with
reflective methods such as


java.lang.Class.getDeclaredMethod(String, Class[])


although void.class probably only occurs as the return value of


java.lang.reflect.Method.getReturnType()


Class literals (anything with ".class") are syntactic sugar which the
compiler maps to other constructs:


void.class java.lang.Void.TYPE


int.class java.lang.Integer.TYPE


int[][][].class Class.forName("[[[I")


Foo.class Class.forName("fully.qualified.name.of.Foo")


Foo[][][].class Class.forName("[[[Lfully.qualified.name.of.Foo;")


In practice the call to Class.forName() is done once and then cached in a
static field, and ClassNotFoundException is mapped to NoClassDefFoundError.


You could argue that int.class et al and void.class are unnecessary,
since you can just as well write Integer.TYPE and Void.TYPE, but overall
I'm glad that the ".class" sugar exists because, unlike Class.forName(),
it can be checked at compile time.


Thomas Maslen
maslen@pobox.com

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