Java Reference
In-Depth Information
88 2
110 3
97 4
99 5
109 6
82 7
116 8
99 9
114 10
$
The next step is to run these through a statistical program to see how really random they are;
we'll return to this in a minute.
In general, to generate random numbers, you need to construct a
java.util.Random
object
(not just any old random object) and call its
next*()
methods. These methods include
nex-
tBoolean()
,
nextBytes()
(which fills the given array of bytes with random values),
nex-
tDouble()
,
nextFloat()
,
nextInt()
, and
nextLong()
. Don't be confused by the capitaliz-
ation of
Float
,
Double
, etc. They return the primitive types
boolean
,
float
,
double
, etc.,
not the capitalized wrapper objects. Clear enough? Maybe an example will help:
// java.util.Random methods are non-static, so need to construct
Random r
=
new
new
Random
();
for
for
(
int
int
i
=
0
;
i
<
10
;
i
++)
System
.
out
.
println
(
"A double from java.util.Random is "
+
r
.
nextDouble
());
for
for
(
int
int
i
=
0
;
i
<
10
;
i
++)
System
.
out
.
println
(
"An integer from java.util.Random is "
+
r
.
nextInt
());
You can also use the
java.util.Random nextGaussian()
method, as shown next. The
nextDouble()
methods try to give a “flat” distribution between 0 and 1.0, in which each
value has an equal chance of being selected. A Gaussian or normal distribution is a bell-
curve of values from negative infinity to positive infinity, with the majority of the values
around zero (0.0).
// Random3.java
Random r
=
new
new
Random
();
for
for
(
int
int
i
=
0
;
i
<
10
;
i
++)
System
.
out
.
println
(
"A gaussian random double is "
+
r
.
nextGaussian
());
