Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: markspace <markspace@nospam.nospam>
Newsgroups: comp.lang.java.programmer
Subject: Re: StringBuilder.append and CharSequence
Date: Wed, 25 Sep 2013 18:34:14 -0700
Organization: A noiseless patient Spider
Lines: 43
Message-ID: <l202uq$ae1$1@dont-email.me>
References: <slrnl45s71.mol.avl@gamma.logic.tuwien.ac.at> <l1vfg6$mi$1@dont-email.me>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 26 Sep 2013 01:34:18 +0000 (UTC)
Injection-Info: mx05.eternal-september.org; posting-host="9185b88a2b5381a82810209530bb8295"; logging-data="10689"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/ZCXFICS4sMWV6/0rYZm5e1Z3/ROnWxGs="
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
In-Reply-To: <l1vfg6$mi$1@dont-email.me>
Cancel-Lock: sha1:frJHpPhKzQsBDM9V/68H5rTR9Q4=
Xref: csiph.com comp.lang.java.programmer:25345

On 9/25/2013 1:02 PM, markspace wrote:
> On 9/25/2013 7:19 AM, Andreas Leitgeb wrote:
>> Is it safe to use "stringBuilder.append(this);"
>
> It wasn't clear to me either from reading the Java docs that the above
> was safe, so I'd avoid it.
>
>> in a CharSequence
>> implementation's .toString(), or could this lead to a recursive
>> loop, if some version of a Java class library implements the
>> append() for CharSequence by using it's toString() ?
>
> That paragraph wasn't clear to me at all.  I was going to suggest
> toString() as the safe approach.
>
>    stringBuilder.append( this.toString() );
>
> This seems bomb proof to me, as the string is constructed before the
> method call.  Did I miss something?

Actually, I mis-read your problem statement, I think.  Having 
implemented a couple of CharSequence classes, the only rational approach 
would be to copy the chars out of a CharSequence one at a time with a 
loop and charAt().  toString() must create an immutable String and so 
must create a new buffer, so that's an extra buffer copy, which seems 
undesirable no matter who's implementing the append() method.  However I 
wouldn't call toString(), as that would obviously create a stack overflow.

I would think that you must have some much better method of copying 
characters though, as you should have access to your own private fields.

   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append( myCharArray, start, length );
     return sb.toString();
   }

This obviously could be done with a single "new String(..." but I'm just 
trying to hammer the idea home that there's internal fields to use.