Object with primitive type equality operator and Java Language specification

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Mon Jul 13 20:37:55 UTC 2015

I believe you are staring at this:


Which was fixed in JDK 8 - long story short, javac compiler has 
historically performed operator checks by means of pseudo operator 
overloading (i.e. the internal compiler symbol table had entries for the 
various kind of allowed ''overloaded' operators, and the overload logic 
would do the rest). Needless to say, this behavior was not 100% 
conformant w.r.t. JLS and it had few bugs as in this case.

We worked around the problem in JDK 8 by applying a local fix which got 
rid of the issue - in JDK 9 we completely removed the root cause:


So that, moving forward, we hope that these kind of discrepancies should 
be a thing of the past (finger crossed :-)).


On 13/07/15 19:32, Alex Buckley wrote:
> The JLS section on == is rather stable, and has always rejected the 
> code below. Object isn't convertible to a numeric type, and int isn't 
> a reference type, and either type is boolean or Boolean, so no 
> equality operator is available.
> javac historically had some problems with operators taking Object and 
> a numeric type (or rather, taking expressions of those types), but I 
> believe this was cleaned up a couple of years ago, and JDK 8 correctly 
> rejects the code below.
> FWIW, if you cast num to Object to the right of == (legal by JLS8 
> 5.5), then JDK 8 correctly compiles the code. The output is 'true' 
> because of the flyweight pattern applied to boxed integer literals 
> between -128 and 127. If you make both integer literals in the code be 
> 128, then the output is 'false'.
> Alex
> On 7/13/2015 11:09 AM, Rostislav Krasny wrote:
>> Hi,
>> javac of JDK7 successfully compiles a code like following:
>> public class MainClass {
>>      private static Object getValue() {
>>          return 123;
>>      }
>>      public static void main(String[] args) {
>>          int num = 123;
>>          System.out.println(getValue() == num);
>>      }
>> }
>> I believe javac of other JDKs, starting from JDK5, also compile such a
>> code without any problem. However Eclipse and its Java compiler fails to
>> compile the Object with primitive type equality (getValue() == num) with
>> an error "Incompatible operand types Object and int". There is a bug
>> report about this in the Eclipse Bugzilla:
>> https://bugs.eclipse.org/bugs/show_bug.cgi?id=405732
>> This bug was closed as NOT_ECLIPSE, i.e. developers of Eclipse Java
>> compiler believe their compiler do it right. Please read the discussion
>> in that bug report.Specifically Stephan Herrmann stated that Java
>> Language specification disallows compiling such a code. So is it a bug
>> in the javac compiler itself? Or maybe the JLS needs to be changed to
>> conform to the long ago adopted javac compiler implementation? Or there
>> is the JLS misunderstanding?
>> Thanks

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