Java Reference
In-Depth Information
versions do not apply everywhere, and in particular you cannot directly
dereference a primitive variable, or value, as if it were an object. For
example, given the
int
variable
x
, as above, the expression
x.toString()
will not compile. You can, however, apply a cast to the primitive first,
such as:
((Object) x).toString()
The exact contexts in which boxing and unboxing automatically occur
are discussed in "
Type Conversions
"
on page
216
.
Ideally, you would rely on boxing conversions wherever necessary,
without giving it a second thought. In practice, you need to be aware
that a boxing conversion may need to allocate an instance of a wrapper
class, which consumes memory and which may fail if insufficient
memory is available. Given that the wrapper classes are immutable, two
objects with the same value can be used interchangeably, and there
is no need to actually create two distinct objects. This fact is exploited
by requiring that boxing conversions for certain value ranges of certain
types always yield the same object. Those types and value ranges are:
Type
Range
true
,
false
boolean
all values
byte
\u0000
to
\u00ff
char
-128
to
127
short
