Object with primitive type equality operator and Java Language specification

Alex Buckley alex.buckley at oracle.com
Mon Jul 13 18:32:47 UTC 2015

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'.


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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