Re: Enums
Lew wrote :
On Aug 24, 3:36?pm, Wojtek <nowh...@a.com> wrote:
Lew wrote :
Alessio Stalla wrote :
You can persist the name of the constant, and retrieve the Enum
instance with Enum.valueOf(MyEnum.class, name). Or, depending on the
context, you can persist the serialized Enum (enums are serializable
by default).
Wojtek <nowh...@a.com> wrote:
Ok.
But, silly me, I sometimes rename Enum values. Yes, yes, poor design
and all, but it happens.
And that doesn't risk changing the ordinal? ?Or if there were a way to
set the ordinal (as there is, as long as by "ordinal" you mean a
custom value retrieved by a method 'getOrdinal()') what's to prevent
you from changing that?
// do not change as it is persisted!
private static final int MY_ENUM_ID = 1;
public enum IsEnum
{
? ?MY_ENUM(MY_ENUM_ID);
? ?private int id;
? ?private IsEnum( int databaseID )
? ?{
? ? ?id = databaseID;
? ?}
? ?public int getDatabaseID()
? ?{
? ? ? return id;
? ?}
}
and then, of course, some code to scan the enums and find the id you
are looking for.
This is safe against the Java compiler setting ordinals and renaming
enums.
But it is not safe against the programmer redefining 'MY_ENUM_ID',
which is the same degree of change as altering the enum constant name
or an assigned string name. It's equivalent to the suggestion
upthread to add 'fromString()' and override 'tostring()' to match,
with a 'String' identifier instead of an 'int', and has the same
degree of safety (danger).
Not true. The comment warning is there. But renaming the enum may
produce greater code readability. Whereas changing the constant
improves nothing and so is more or less immune to changes, that is a
future programmer would have no incentive to change it.
Heck, I could have used:
MY_ENUM(1)
just as easily. And after the compiler creates the byte code that is
probably what it ends up as. I just like to break it out...
All you really show in your example is substitution of one constant,
the 'int', for another, the 'enum' value. Enums are a type-safe
replacement for compile-time constants such as 'MY_ENUM_ID'; using
them together like that is redundant.
Not redundant. An int is an int, but an enum can only be THAT enum.
Which is why enums exist in the first place.
But since ordinal values are under the compiler's control I use a value
which is under MY control for persistance.
--
Wojtek :-)