RFR [16/java.xml] 8248348: Regression caused by the update to BCEL 6.0

[Joe Wang]

Hi,

Please review a fix to a BCEL regression. At issue was the addition of 
hashCode() method to Instruction.java in BCEL 6.0. This hashCode() 
method was implemented to return the instruction's opcode that 
unfortunately is mutable. The problem hasn't showed up until the code 
path led to calls to remove from a HashSet a target that has been 
changed since it was added to the HashSet. The proposed patch is to make 
the hashCode final/immutable.

This patch implies that a target object is considered the same one even 
if its field values may have been changed. It therefore may not be 
appropriate in other situations (or may cause problems). However, since 
it had always had no hashCode() override before BCEL 6.0, thereby 
relying on Object's identity hash code, its use case has been limited 
and time-tested. It can benefit from this patch in that it provides the 
same function as Object's hash code, and then serves as a reminder (to 
any who might read the code) how it was used (objects considered to be 
the same over the course as far as the hashCode is concerned).

JBS: https://bugs.openjdk.java.net/browse/JDK-8248348
webrevs: http://cr.openjdk.java.net/~joehw/jdk16/8248348/webrev/

Thanks,
Joe