Hi Joe, For an object to correctly function as an element of a HashSet, its hashCode() and equals() methods must agree: o1.equals(o2) => o1.hashCode() == o2.hashCode(). I see equals() method delegates to a global InstructionComparator instance which can even change. Suppose it does not change. But what does such InstructionComparator compare? opcode (among other things)?
Regards, Peter On Fri, 26 Jun 2020, 01:56 Joe Wang, <huizhe.w...@oracle.com> wrote: > 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 > >
