Why I can not get .values() from Enum object class?

Question

I want to create universal method, for any enum object, that will check if enum has specified value name, but as Enum type object I am unnable to use method values();. Why?

Is there any way to get values from an Enum type object?

I need method like this to check if value from configuration is a valid string for myEnum.valueOf(String); because if given string will be wrong then it will throw an exception (and I do not want it).

I want my method to look like this:

public static Boolean enumContains(Enum en, String valueString){
    return toStringList(en.values()).contains(valueString.toUpperCase());
}

But there is no method Enum.values(). How to create this method correctly?

I want to make it universal, so I put just `Enum` as type of argument to match any `Enum` object to this method. — Albert451, Dec 16 '18 at 17:28
And `values` does only work for the `enum` type, e.g. `MyEnum.values()` but clearly not for a specific value of an `enum` like in your method... — UninformedUser, Dec 16 '18 at 17:29
ok, that can't work for any enum as explained by the others in the comment — UninformedUser, Dec 16 '18 at 17:29
Reflection would also be a workaround, but who wants to use reflection...`getDeclaredField("$VALUES");` or `Enum.class.getDeclaredMethod("values");` for the enum class — UninformedUser, Dec 16 '18 at 17:31
So how to create this method propetly without reducing it to single type of enum like MyEnum? I want to create it for any enum object — Albert451, Dec 16 '18 at 17:31
@AKSW Your hack relies on a specific implementation of enums which may not be true for all Java implementations. And `getDeclaredField` is, in fact, using reflection. — RealSkeptic, Dec 16 '18 at 17:36
@RealSkeptic I know, never said this is a solution nor did I provide it as an answer. — UninformedUser, Dec 16 '18 at 17:41

score 6 · Accepted Answer · answered Dec 16 '18 at 17:33

Enum#values is a method that is generated by the compiler, so you cannot use it at compile time unless you pass in a specific enum and not Enum<?>.

See: https://stackoverflow.com/a/13659231/7294647

One solution would be to pass in a Class<E extends Enum<E>> instead and use Class#getEnumConstants:

public static <E extends Enum<E>> Boolean enumContains(Class<E> clazz, String valueString){
    return toStringList(clazz.getEnumConstants()).contains(valueString.toUpperCase());
}

If you have an enum named MyEnum, then you can simply pass in MyEnum.class as the first argument.

Why I can not get .values() from Enum object class?

1 Answers1

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