When is it legal to compare Objects and primitives with '==' operator?

Question

Is the below (Java) code legal?

class Test {
  Object foo() {return "";}
  boolean bar() {return foo() == true;}
}

It won't compile against JDK 6 but seems fine on 7+. Did the spec change? Was a bug fixed? I've been discussing at http://bugs.eclipse.org/bugs/show_bug.cgi?id=416950 and could go either way on this one.

Answer 1

JLS about reference equality doesn't change between java 6 & 7:

Chapter 15.21.3: Reference Equality Operators == and != :

If the operands of an equality operator are both of either reference type or the null type, then the operation is object equality.

It is a compile-time error if it is impossible to convert the type of either operand to the type of the other by a casting conversion (§5.5). The run-time values of the two operands would necessarily be unequal.

However I noticed some change on Chapter 5.5: Casting Conversion. Casting boolean to Object appears to be classified as boxing convention on Java 7:

An expression of a primitive type may undergo casting conversion to a reference type without error, by boxing conversion.

⊡ signifies boxing conversion

Hence since the primitive true can be casted to Object, your equality expression can be classified as reference equality on Java 7, and doesn't yield compiler error