Effective Java

return ordinal() + 1;
}
}
While this enum works, it is a maintenance nightmare. If the constants are
reordered, the 
numberOfMusicians
method will break. If you want to add a sec-
ond enum constant associated with an 
int
value that you’ve already used, you’re
out of luck. For example, it might be nice to add a constant for 
double quartet
,
which, like an octet, consists of eight musicians, but there is no way to do it.
Also, you can’t add a constant for an 
int
value without adding constants for
all intervening 
int
values. For example, suppose you want to add a constant repre-
senting a 
triple quartet
, which consists of twelve musicians. There is no standard
term for an ensemble consisting of eleven musicians, so you are forced to add a
dummy constant for the unused 
int
value (
11
). At best, this is ugly. If many 
int
values are unused, it’s impractical.
Luckily, there is a simple solution to these problems. 
Never derive a value
associated with an enum from its ordinal; store it in an instance field instead:
public enum Ensemble {
SOLO(1), DUET(2), TRIO(3), QUARTET(4), QUINTET(5),
SEXTET(6), SEPTET(7), OCTET(8), DOUBLE_QUARTET(8),
NONET(9), DECTET(10), TRIPLE_QUARTET(12);
private final int numberOfMusicians;
Ensemble(int size) { this.numberOfMusicians = size; }
public int numberOfMusicians() { return numberOfMusicians; }
}
The 
Enum
specification has this to say about 
ordinal
: “Most programmers
will have no use for this method. It is designed for use by general-purpose enum-
based data structures such as 
EnumSet
and 
EnumMap
.” Unless you are writing code
with this character, you are best off avoiding the 
ordinal
method entirely.

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ITEM 36: USE ENUMSET INSTEAD OF BIT FIELDS
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