Re: StringBuffer/StringBuilder efficiency
Roedy Green wrote:
....
Another StringBuilder optimisation that would be useful would be if
the estimate of StringBuilder size were accurate to say with 10 bytes,
then the buffer could be converted to a String without copying it.
....
This would take some care, given the mutable nature of StringBuilder,
but would be possible, given the fact that String and StringBuilder are
in the same package.
One possible design:
1. Add to String a package-only constructor that sets the char[],
length, and offset fields directly.
2. Modify StringBuilder:
Add a boolean field sharedArray, initially false.
In toString, if size is accurate enough, use the new String constructor
and set sharedArray=true.
In state changing method calls that use the old value, such as append,
with sharedArray true, replace the reference to the shared char[] with a
reference to a copy of it and set sharedArray=false.
The only state changing method call I have identified that does not use
the old value is delete with a range covering the whole string. In that
case, if sharedArray, replace the char[] with a new one, and set
sharedArray=false.
Of course, this is mainly precautionary. Often, a toString() call is the
last event in the life of a StringBuilder before unreachability.
Patricia