RFR: 8071571: Move substring of same string to slow path

[John Rose]

On Mar 27, 2015, at 3:01 PM, Martin Buchholz <martinrb at google.com> wrote:
> 
> final Type foo = this.foo;

There are IMO a few places where local finals pay for themselves,
even after Java 8.

One is Martin's idiom.  The key thing to observe is that 'foo' is
a read-only snapshot or view of 'this.foo'.  If we were after
conciseness (only) we could delete the whole line, but the line
as a whole has a clear purpose.

Another reasonable use of local finals is when writing SSA-style code.
A blank final enforces SSA, and makes it clearer what's going on.

If I'm writing a large, complex loop and I want to make it clear that
something is loop-invariant, I sometimes use a final.  But in cases
like that it's better to factor the loop body into a separate method,
if that is possible.

Another place I like finals is where I am capturing values which
are constants, sampled from a variable (e.g., "cursor++").  In
that case, the different declaration makes clear the distinction
between a snapshot and a varying cursor.  This is of course
a matter of taste.

In all these cases the benefits are only present when the affected
variable has a large or complex live range.  So the best use
cases are always going to give the onlooker a sense of unease.
In simple use cases, "final" is just noise, but in complex ones
it can help solidify the reader's understanding.

— John