side note on static array constants and final fields

[John Rose]

A side note on the unsigned-byte conversation:

Static finals are treated by the JIT as constants, and a few of their  
built-in immutable fields are (recursively) compile time constants.

The oop _klass and array _length fields are both compile-time  
constants, whenever the enclosing object reference is constant.  This  
is why you get benefit from making static arrays final; their range  
checks fold up.

Some day we'll extend this treatment to user-written final instance  
fields, so whole nests of objects can be folded more aggressively in  
the JIT.  It's tricky, though, since user-written finals are not  
truly immutable:  According to the verifier, they can be written and  
even rewritten in their own constructors.

-- John

On Jan 17, 2009, at 1:35 PM, Ulf Zibis wrote:

> + the map should be defined final.
>