RFR: JDK-8074002 java.time.ZoneId.systemDefault() should be faster

[Peter Levart]

Hi,

Please review the following improvement that caches default ZoneId 
object and makes the frequently executed ZoneId.systemDefault() method 
faster:

http://cr.openjdk.java.net/~plevart/jdk9-dev/ZoneId.systemDefault/webrev.04/

The patch is just a rebased version of webrev.03 + some comments added 
about the importance of defensive cloning in TimeZone.setDefault(). 
There was already a discussion about this patch a while ago and Stephen 
basically approved it in this form:

http://mail.openjdk.java.net/pipermail/core-libs-dev/2015-February/031714.html


Thanks,

Peter Levart