Does autoboxing call valueOf()?

Question

I\'m trying to determine whether the following statements are guaranteed to be true:

((Boolean)true) == Boolean.TRUE
((Boolean)true) == Boolean.valueOf(true)         


        

Answer 1

Until the language specification mentions it, it is not guaranteed that autoboxing is equivalent to a call to the static valueOf methods. It is an implementation aspect, not part of the boxing conversion specification. An implementation is theoretically free to use another mechanism as long as it conforms to the rule you mentioned from the JLS.

In practice, there are many Sun JDK bug reports (e.g. JDK-4990346 and JDK-6628737) that clearly imply that when autoboxing was introduced in Java 5, the intention was having the compiler to rely on valueOf as stated in JDK-6628737:

The static factory methods Integer.valueOf(int), Long.valueOf(long), etc. were introduced in JDK 5 for javac to implement the caching behavior required by the autoboxing specification.

But that's only for javac, not necessarily all compilers.