Proposal: Improved Wildcard Syntax for Java (original) (raw)

Joseph D. Darcy Joe.Darcy at Sun.COM
Thu Mar 19 01:38:37 PDT 2009

Howard Lovatt wrote:

Hi Joe,

Thanks for the response, answers in text. 2009/3/18 Joseph D. Darcy <Joe.Darcy at sun.com> wrote: [snip]

1. Deprecate raw declarations, new ArrayList() becomes a deprecated warning - you need to say new ArrayList(). > That could be a fine lint option. You could also write an annotation > processor that used the javac tree API to generated such warnings/errors > today. Yes you could - but I think it would be better in the language so that every implementation gets this useful behaviour.

Language changes are not a quick way to enact change. It is certainly possible that all implementations of interest can get a desirable feature without a language change and that such universal changes are usable sooner than a language change can be made officially available.
All Java SE 6 compiler implementations are required to support annotation processing and each that I'm aware of has a tree API to provide additional information; therefore, additional checks that can easily be written as annotation processors are much better implemented and promulgated as annotation processors.

2a. Deprecate self references, you get a deprecated warning for class Type<T extends Type>, you wouldn't use generics in this case.

F-bounds are part of Java's generics. Yes. But I am suggesting that we deprecate it because no one likes it.

Simply because a feature is complicated or disliked doesn't imply it isn't technically desirable or necessary!

The complication and confusion that it brings outweighs its benefit. Less is more.

[snip]

3. Deprecate the ability to specify multiple bounds, e.g. instead of static <T extends Object & Comparable<? super T>> T max(Collection<?_ _extends T>) you write static T max(Collection) (note Comparable would not be parameterised with the new syntax since you would almost always want Comparable). > There are reasons why multiple bounds are supported. Yes. Again not worth the trouble - don't use generics in these backward compatibility cases.

The multiple bounds and the trick of putting Object as the first bound to maintain the desired erasure were added in JDK 5 to solve actual problems; see Gilad's "Generics in the Java Programming Language." http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf

-Joe

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