Avoid Enums
Enums are very convenient, but unfortunately can be painful when size
and speed matter. For example, this:
public class Foo {
public enum Shrubbery { GROUND, CRAWLING, HANGING }
}
turns into a 900 byte .class file (Foo$Shrubbery.class). On first use, the
class initializer invokes the <init> method on objects representing each
of the enumerated values. Each object gets its own static field, and the full
set is stored in an array (a static field called "$VALUES"). That's a lot of
code and data, just for three integers.
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.
The flip side, of course, is that with enums you get nicer APIs and
some compile-time value checking. So, the usual trade-off applies: you should
by all means use enums for public APIs, but try to avoid them when performance
matters.
In some circumstances it can be helpful to get enum integer values
through the ordinal() method. For example, replace:
for (int n = 0; n < list.size(); n++) {
if (list.items[n].e == MyEnum.VAL_X)
// do stuff 1
else if (list.items[n].e == MyEnum.VAL_Y)
// do stuff 2
}
with:
int valX = MyEnum.VAL_X.ordinal();
int valY = MyEnum.VAL_Y.ordinal();
int count = list.size();
MyItem items = list.items();
for (int n = 0; n < count; n++)
{
int valItem = items[n].e.ordinal();
if (valItem == valX)
// do stuff 1
else if (valItem == valY)
// do stuff 2
}
In some cases, this will be faster, though this is not guaranteed.
