Craig,
Excellent explanation!
John D. McDonald
-----Original Message-----
From: Craig R. McClanahan <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Monday, August 16, 1999 1:10 PM
Subject: Re: (SUGGESTION) OutOfMemoryException
>Tim Crook wrote:
>
>> Hi Giovanni.
>>
>> I know this is recommended general practice for Strings, but if you are
>> using JDK 1.2, wouldn't using HotSpot eliminate the need for hand
optimizing
>> code like this?
>>
>
>HotSpot can make many kinds of code faster, but it's still going to be
faster
>yet to use a StringBuffer.
>
>The reason for this is that HotSpot still has to obey the rules of the Java
>Language Specification, which says that Strings are immutable (i.e. you
cannot
>change them after they are created). Whenver you ask for a concatenation,
a
>new String has to be constructed When you say
>
> String value = "abc";
> value += "def";
>
>what you are really saying, using an optimized implementation, is in
essence:
>
> String value = "abc";
> {
> StringBuffer temp = new StringBuffer(value);
> temp.append("def");
> value = temp.toString();
> }
>
>Thus, you're creating a new object and doing an object-to-String conversion
at
>the end, for *every* use of "+=". The same kind of thing happens when you
use
>the "+" concatenation operator in an expression. If you use the
StringBuffer
>approach, you only create a StringBuffer once, you only have to incur the
>method call for append() for each addition, and you only pay the toString()
>price once at the end.
>
>Moral of the story: concatenating strings with a StringBuffer will always
be
>faster -- enough faster that you should retrain your fingers to code this
kind
>of thing correctly the first time, every time.
>
>Craig McClanahan
>
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