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From: Stanimir Stamenkov <s7an10@netscape.net>
Newsgroups: comp.lang.java.programmer
Subject: Re: StringBuilder
Date: Sun, 18 Sep 2011 17:08:28 +0300
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Sun, 18 Sep 2011 09:50:03 -0400, /Eric Sosman/:
> On 9/18/2011 9:32 AM, Jan Burse wrote:
>
>> I guess first of all probably a reengineering was done, and
>> StringBuffer was split into AbstractStringBuilder and StringBuffer.
>> And then StringBuilder was created. The class diagramm is basically:
>>
>>           AbstractStringBuilder
>>           /                    \
>>       StringBuffer             StringBuilder
>
>      I do not know whether buffer-sharing was dropped before, after,
> or with the introduction of StringBuilder.

I don't know when the implementation has changed, also, but here's 
my guess on why it might have changed to make a copy.  Previously 
I've often used:

     StringBuffer buf;
     ...
     String str = buf.substring(0, buf.length());

to have the constructed String internal char[] always occupying 
exactly the size needed to hold the text.  Previously, with 
StringBuffer.toString() the String could hold as much as twice 
bigger char[] than needed.  If one constructs long lived String 
objects that way, the memory usage could grow unnecessary high.

-- 
Stanimir