RFR(S): 8067471: Use private static final char[0] for empty Strings

[Remi Forax]

On 12/17/2014 11:22 AM, Lev Priima wrote:
> Hi,
>
> Please review space optimization in no args String constructor. 
> Originally, it was already rejected once by suggestion in 
> http://mail.openjdk.java.net/pipermail/core-libs-dev/2012-May/010300.html 
> w/o formal justification of pros and contras.  And enhancement was 
> requested again by Nathan Reynolds.
>
> Issue: https://bugs.openjdk.java.net/browse/JDK-8067471
> Patch: http://cr.openjdk.java.net/~lpriima/8067471/webrev.00/
>

Hi Lev,
new String() is usually used by beginners that forget or doesn't know 
that you they can use "" instead.
There is only one legit usage when you want a NullObject for a String 
*and* you don't want to have a shared reference (something visible by 
everybody).

You find 4 occurences of new String() in the JDK,
 > jdk.httpserver/share/classes/sun/net/httpserver/Request.java:200: v = 
new String();
 > java.base/share/classes/sun/net/www/MessageHeader.java:508: v = new 
String();
 > 
java.base/share/classes/java/lang/invoke/MethodHandles.java:829:MethodType 
MT_newString = methodType(void.class); //()V for new String()
 > 
jdk.runtime/share/classes/sun/security/tools/policytool/PolicyTool.java:947: 
String stringEntry = new String();

For the first two, the code is very similar and "" can be used instead 
of new String().
The third occurence is just a comment.
The last occurence is typically a code written by a beginner, the code 
use String.concat, do a kind of defensive copy on String (line 967). 
Again, "" can be used instead of new String().

so my suggestion is to wait to have more information from Nathan 
Reynolds before trying to fix something,
new String() is not the only way to have a String with an empty char array.

cheers,
Rémi