enum on OCA exam objectives

[Nhien Nguyen]

Hi, I'm wondering as whether enum is still on the objective topic of the OCA since I don't see Sybex mention this.

[Pete Letkeman]

Most likely questions regarding enum will not be on the Java 808 OCA exam.
That said, for the OCA level of questions, enums can be thought of as final classes.

[Teodor Ian]

@Pete Letkeman, Sorry for my greenhorn arrogance but are you sure that an enum class can be final?  (of course enums themselves are always final)

https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.9
"It is a compile-time error if an enum declaration has the modifier abstract or final."

[Campbell Ritchie]

Welcome to the Ranch
What is the difference between an “enum class” and an enum? Pete said that enums are final classes, which matches what the Java® Language Specification says.

[Paul Clapham]

https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.9

"It is a compile-time error if an enum declaration has the modifier abstract or final.
An enum declaration is implicitly final unless it contains at least one enum constant that has a class body (§8.9.1)."

[Jeanne Boyarsky]

Enums are on page 72 of the Sybex 1Z0-808 book.

[Teodor Ian]

Thank you very much, now I understand.
The misunderstanding was that English is not my mother tongue and I translated in my head: "enum can be thought of as a final class".

[Campbell Ritchie]

Quoting from the JLS link given earlier.

Paul Clapham wrote:. . . An enum declaration is implicitly final unless it contains at least one enum constant that has a class body (§8.9.1)."

I think I misunderstood that bit about implicitly final at first. I thought that meant that an enum with class bodies can be extended by a different XXX.java file or compilation unit. I think it actually means that enums with class bodies extend themselves. They cannot be extended elsewhere. The constants with class bodies look like instances of anonymous classes. I don't know whether they really are anonymous classes.
If you write a compilation unit extending an enum with class bodies for every constant, e.g. the Operation enum from the Java™ Language Specification (=JLS), you will see you get a compiler error.
If you go through the first JLS link I gave you, you will find out why you can't write enum XYZ extends...