Java Reference
In-Depth Information
is a type cast. The expression takes an
int
(in this example the value of
m
) and evalu-
ates to an “equivalent” value of type
double
. So, if the value of
m
is
2
, the expression
(double)m
evaluates to the
double
value
2.0
.
Note that
(double)m
does not change the value of the variable
m
. If
m
has the value
2
before this expression is evaluated, then
m
still has the value
2
after the expression is
evaluated.
You may use other type names in place of
double
to obtain a type cast to another
type. We said this produces an “equivalent” value of the target type. The word “equiv-
alent” is in quotes because there is no clear notion of equivalent that applies between
any two types. In the case of a type cast from an integer type to a floating-point type,
the effect is to add a decimal point and a zero. A type cast in the other direction, from
a floating-point type to an integer type, simply deletes the decimal point and all digits
after the decimal point. Note that when type casting from a floating-point type to an
integer type, the number is truncated not rounded:
(int)2.9
is
2
; it is not
3
.
As we noted earlier, you can always assign a value of an integer type to a variable of
a floating-point type, as in
double
d = 5;
In such cases Java performs an automatic type cast, converting the
5
to
5.0
and placing
5.0
in the variable
d
. You cannot store the
5
as the value of
d
without a type cast, but
sometimes Java does the type cast for you. Such an automatic type cast is sometimes
called a
type coercion
.
By contrast, you cannot place a
double
value in an
int
variable without an explicit
type cast. The following is illegal:
type coercion
int
i = 5.5; //Illegal
Instead, you must add an explicit type cast, like so:
int
i = (
int
)5.5;
Increment and Decrement Operators
The
increment operator
++ adds one to the value of a variable. The
decrement oper-
ator
−−
subtracts one from the value of a variable. They are usually used with variables
of type
int
, but they can be used with any numeric type. If
n
is a variable of a numeric
type, then
n++
increases the value of
n
by one and
n
−−
decreases the value of
n
by one.
So,
n++
and
n
−−
(when followed by a semicolon) are executable statements. For exam-
ple, the statements
int
n = 1, m = 7;
n++;
System.out.println("The value of n is changed to " + n);
m
−−
;
System.out.println("The value of m is changed to " + m);
