What is Enum useful for? [duplicate]

Question

After reading some questions and answers about enum I don't find it really useful...

It's something between class and a variable but I know where can I use it so it would be more useful then a class, or a couple of variables for example.

Answer 1

There are other things you can do and reasons to use them, but the primary reason I use enums is to prevent the possibility of an invalid parameter. For example, imagine the following method:

public void doSomethingWithAMonth(int monthNum);

This is not only ambiguous (do month indexes start at 1, or at 0?), but you can give down-right invalid data (13+, negative numbers). If you have an enum Month with JAN, FEB, etc. the signature becomes:

public void doSomethignWithAMonth(Month month);

Code calling this method will be far more readable, and can't provide invalid data.

Answer 2

I use Enums for anything that has multiple nonchanging "type" of something. i.e days of a week.

Why I don't use String in this case is because I can't do switch statement on the String and I can on Enum so for every day of a week I can do something specific.

I also use Enum when working with singleton pattern, Check the Effective Java book CH2(CHAPTER 2 CREATING AND DESTROYING OBJECTS), quote :

"While this approach has yet to be widely adopted, a single-element enum type is the best way to implement a singleton." not gonna paste code read the book it's excellent.

If I were you I'd firstly read Thinking in java chapter Enumerated Types. Then after that Effective Java chapter 6 and you should be good