Java Reference
In-Depth Information
It is fine to declare
i
in two
nonnested blocks.
It is wrong to declare
i
in two
nested blocks.
public static void
method1() {
int
x =
1
;
int
y =
1
;
public static void
method2() {
int
=
1
;
int
sum =
0
;
i
for
(
int
i
=
1
; i <
10
; i++) {
x += i;
for
(
int
i
=
1
; i <
10
; i++)
}
sum += i;
}
for
(
int
i
=
1
; i <
10
; i++) {
y += i;
}
}
}
F
IGURE
5.6
A variable can be declared multiple times in nonnested blocks, but only once in nested blocks.
Caution
Do not declare a variable inside a block and then attempt to use it outside the block.
Here is an example of a common mistake:
for
(
int
i =
0
; i <
10
; i++) {
}
System.out.println(i);
The last statement would cause a syntax error, because variable
i
is not defined outside
of the
for
loop.
5.20
✓
✓
What is a local variable?
Check
5.21
What is the scope of a local variable?
Point
The
Math
class contains the methods needed to perform basic mathematical functions.
Key
Point
a
b
You have already used the
pow(a, b)
method to compute in Section 2.9.3, Exponent Oper-
ations, and the
Math.random()
method in Section 3.8, Generating Random Numbers. This
section introduces other useful methods in the
Math
class. They can be categorized as
trigonometric methods
,
exponent methods
, and
service methods.
Service methods include the
rounding, min, max, absolute, and random methods. In addition to methods, the
Math
class pro-
vides two useful
double
constants,
PI
and
E
(the base of natural logarithms). You can use these
constants as
Math.PI
and
Math.E
in any program.
5.10.1 Trigonometric Methods
The
Math
class contains the following trigonometric methods:
/** Return the trigonometric sine of an angle in radians */
public static double
sin(
double
radians)
/** Return the trigonometric cosine of an angle in radians */
public static double
cos(
double
radians)
/** Return the trigonometric tangent of an angle in radians */
public static double
tan(
double
radians)
