It’s worth mentioning that the following expression:
new Long(10).equals(new Integer(10))
is always false
, which tends to trip everyone up at some point or another. So not only can you not compare arbitrary Number
s but you can’t even determine if they’re equal or not.
Also, with the real primitive types (float
, double
), determining if two values are equal is tricky and has to be done within an acceptable margin of error. Try code like:
double d1 = 1.0d;
double d2 = 0.0d;
for (int i=0; i<10; i++) {
d2 += 0.1d;
}
System.out.println(d2 - d1);
and you’ll be left with some small difference.
So back to the issue of making Number
Comparable
. How would you implement it? Using something like doubleValue()
wouldn’t do it reliably. Remember the Number
subtypes are:
Byte
;Short
;Integer
;Long
;AtomicInteger
;AtomicLong
;Float
;Double
;BigInteger
; andBigDecimal
.
Could you code a reliable compareTo()
method that doesn’t devolve into a series of if instanceof statements? Number
instances only have six methods available to them:
byteValue()
;shortValue()
;intValue()
;longValue()
;floatValue()
; anddoubleValue()
.
So I guess Sun made the (reasonable) decision that Number
s were only Comparable
to instances of themselves.