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From: markspace <markspace@nospam.nospam>
Newsgroups: comp.lang.java.programmer
Subject: Re: String.substring in JDK 1.7.0_6+
Date: Sat, 02 Feb 2013 15:31:13 -0800
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On 2/2/2013 2:46 PM, Kevin McMurtrie wrote:

> Some future JVMs do have JIT tricks to improve String performance.  It's
> not clear how that would perform or what the side effects would be.  One

The main think I'd like to see as a "trick" would be to spot when an 
array is not accessed after a copy, thus negating the need for a copy.

String constructor:

   public String( char[] chars ) {
     this.buffer = Arrays.copyOf( chars, chars.length );
   }

Usage:

   public String someMethod() {
     char[] myBuff = ...  // a local variable
     return new String( myBuff );
   }

Spotting that the copy isn't needed because myBuff is local and can't be 
accessed after the return is one obvious optimization.

If this type of analysis is very hard, I can see the original 
implementation of StringBuilder would be advantageous.  OTOH, it doesn't 
look hard, and I'd bet there's a lot of situations where checking a 
"copy-on-write bit" is a bigger performance hit.