Java Reference
In-Depth Information
As Chapter3 ' s Lotto649 applicationrevealed, random() (whichreturnsanum-
ber that appears to be randomly chosen but is actually chosen by a predictable math
calculation, and hence is pseudorandom ) is useful in simulations (as well as in games
andwhereveranelementofchanceisneeded).However,itsdoubleprecisionfloating-
pointrangeof0.0through(almost)1.0isn'tpractical.Tomake random() moreuseful,
its return value must be transformed into a more useful range, perhaps integer values
0through49,ormaybe-100through100.Youwillfindthefollowing rnd() method
useful for making these transformations:
static int rnd(int limit)
{
return (int) (Math.random()*limit);
}
rnd() transforms random() 's 0.0 to (almost) 1.0 double precision floating-point
rangetoa0through limit -1integerrange.Forexample, rnd(50) returnsaninteger
rangingfrom0through49.Also, -100+rnd(201) transforms0.0to(almost)1.0into
-100 through 100 by adding a suitable offset and passing an appropriate limit value.
Caution Donotspecify (int) Math.random()*limit becausethisexpres-
sion always evaluates to 0. The expression first casts random() 's double precision
floating-pointfractionalvalue(0.0through0.99999...)tointeger0bytruncatingthe
fractional part, and then multiplies 0 by limit , resulting in 0.
The sin() and cos() methodsimplementthesineandcosinetrigonometricfunc-
tionsâ€”see
. These functions have uses ranging from the study of triangles
to modeling periodic phenomena (such as simple harmonic motionâ€”see
Wecanuse sin() and cos() togenerateanddisplaysineandcosinewaves. Listing
4-1 presents the source code to an application that does just this.
Listing 4-1. Graphing sine and cosine waves
class Graph
{
final static int ROWS = 11; // Must be odd
final static int COLS= 23;
public static void main(String[] args)
{
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