Question

My suggestions:

1) either enums exist only before compilation (like generics; but I’ve never heard anything about it whilst it’s written everywhere that generics are being erased after compilation)

2) or Enum is a way to maintain backward compatibility in some way (but I don’t see that way yet).

Any other suggestions? (btw, have you ever used it in your code?)

UPD: http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Enum.html

In other words, there’s a enum keyword and Enum class. They both appeared in Java 5. The question: why do we need both?

The second question: why Enum became a part of the API?

Answer 1

From the Java Tutorials:

You should use enum types any time you need to represent a fixed set of constants. That includes natural enum types such as the planets in our solar system and data sets where you know all possible values at compile time—for example, the choices on a menu, command line flags, and so on.

Enums are extremely useful, and yes, I have used them plenty of times in my code.

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Edit:

…there’s a enum keyword and Enum class. They both appeared in Java 5. The question: why do we need both?

This question is analogous to asking “there’s a class keyword and an Object class. Why do we need both?”

In both cases, the keywords are basically hints to the compiler; you could think of them as syntactic sugar that saves you keystrokes, and lets the compiler do less work (by not making it guess about what you’re declaring).

See this q&a as well.

…have you ever used it in your code?

The answer is still “yes.” In particular, Enum#valueOf() is a static method useful for parsing strings:

DayOfWeek d = Enum.valueOf(DayOfWeek.class, "TUESDAY");

but of course this works, too:

DayOfWeek d = DayOfWeek.valueOf("TUESDAY");