Re: Enum Idiom Question

Lew <>
Sat, 29 May 2010 17:23:18 -0400
Rhino wrote:

But am I writing the comparison correctly? That ==
operator looks wrong somehow, even if it works. I'm concerned that this
might be like comparing two Strings with the == operator; sometimes it
show equality and make you think it is confirming equality of value
the two strings but it is not; you have to use equals() to compare
values. But I'm not sure what the equivalent is for an enum.

Lew wrote:

This is fully covered in the docs for enums, ...

Rhino wrote:

In fact, I _did_ read some Java articles on enums and they did NOT mention
that the == operator was the correct one to use.

By "the docs" I'm referring to the JLS and the Javadocs, which are the primary
sources. They don't quite cover everything, but they are canonical as far as
they go.

To whit, the chapter of the language spec that actually defines enums:
says, in paragraph 2 of the first "Discussion" sidebar,

"Because there is only one instance of each enum constant, it is permissible
to use the == operator in place of the equals method when comparing two object
references if it is known that at least one of them refers to an enum
constant. (The equals method in Enum is a final method that merely invokes
super.equals on its argument and returns the result, thus performing an
identity comparison.)"


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