Question

I’ve started to really like using C# and Java enums in my code for several reasons:

• They are much more type-safe than integers, strings, or sets of boolean flags.
• They lead to more readable code.
• It’s more difficult to set an enum to an invalid value than an int or string.
• They make it easy to discover the allowed values for a variable or parameter.
• Everything I’ve read indicates that they perform just as well as integers in C# and most JVMs.

However, the Android framework has numerous cases where flags of various types need to be passed around, but none of them seem to use enums. A couple of examples where I would think their use would be beneficial are Toast.LENGTH_SHORT / Toast.LENGTH_LONG and View.GONE, View.VISIBLE, etc.

Why is this? Do enums perform worse than simple integer values in Dalvik? Is there some other drawback I’m not aware of?

Answer 1

This answer is out of date as of March 2011.

Enums can be used on Froyo and up – according to this answer (Why was “Avoid Enums Where You Only Need Ints” removed from Android’s performance tips?) from a member of the Android VM team (and his blog).

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Previous Answer:

The official Android team recommendation is to avoid enums whenever you can avoid it:

Enums are very convenient, but
unfortunately can be painful when size
and speed matter. For example, this:

public enum Shrubbery { GROUND, CRAWLING, HANGING }

adds 740 bytes to
your .dex file compared to the
equivalent class with three public
static final ints. On first use, the
class initializer invokes the
method on objects representing each of
the enumerated values. Each object
gets its own static field, and the
full set is stored in an array (a
static field called “$VALUES”). That’s
a lot of code and data, just for three
integers. Additionally, this:

Shrubbery shrub = Shrubbery.GROUND;

causes a static field lookup. If
“GROUND” were a static final int, the
compiler would treat it as a known
constant and inline it.

Source: Avoid Enums Where You Only Need Ints