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

[Lev Priima]

Hi Rémi,

Sure this examples will not be affected, but we have to concern about 
other applications which are probably using this constructor. Could you 
suggest such applications?

On 17.12.2014 21:49, Remi Forax wrote:
>
> 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).
One legit usage of which code?
> 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.
just comment to review all MH libs (e.g. nashorn) for such kind of code:
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
publicLookup().findConstructor(String.class, methodType(void.class) 
).invokeExact();
and more implicit variations.
> 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
>
>
>

-- 
Best Regards,
Lev