Why would one want to use the public constructors on Boolean and similar immutable classes?
- by Robert J. Walker
(For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.)
Take Boolean, for example. The documentation for the Boolean(boolean) constructor says:
Note: It is rarely appropriate to use this constructor. Unless a new
instance is required, the static factory valueOf(boolean) is generally
a better choice. It is likely to yield significantly better space and time
performance.
My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null):
if (myBoolean == Boolean.TRUE)
It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead:
if (Boolean.TRUE.equals(myBoolean))
But where it really gets bad is when you want to check two Booleans for equality. Something like this:
if (myBooleanA == myBooleanB)
...becomes this:
if (
(myBooleanA == null && myBooleanB == null) ||
(myBooleanA == null && myBooleanA.equals(myBooleanB))
)
I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?
