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Summary: Math and java.util.Random Classes
Posted on: July 27, 2006 at 12:00 AM
Some basic math functions can be found in the Math class.

Java Summary: Math and java.util.Random Classes

In this section we will discuss Math and java.util.Random classes.

Both these classes can be used for generating the random numbers.

Some basic math functions can be found in the Math class.

The StrictMath class (not described here) may produce less accurate results and be slower, but will produce absolutely identical results, bit for bit, on all machines.

Don't use StrictMath unless you need this very specific kind of portability.

If you need numbers that exceed the range of long, use java.math.BigInteger.

If you need to do exact decimal arithmetic, use java.math.BigDecimal, which gives complete control over precision and rounding, eg for financial calculations.

Assume following declarations

float f;
double d, d1, d2;
double ar;  // angle in radians.
x is any of int, long, float, or double.
Math Constants
Two common constants
 are defined in the Math class.
doubleMath.E() Value of e, 2.718282...,
base of the natural logarithms.
doubleMath.PI() Value of pi, 3.14159265 ....
Math Methods
Trigonometric Methods
All trigonometric method parameters
 are measured in radians, the normal
 mathematical system of angles, and
not in degrees, the normal human
angular measurement system. Use the
 toRadians or toDegrees methods to
convert between these systems, or use
 the knowledge that there are 2*PI
 radians in 360 degrees. In addition
 to those below, the arc functions
 are also available.
doubleMath.sin(ar) Returns the sine of ar.
doubleMath.cos(ar) Returns the cosine of ar.
doubleMath.tan(ar) Returns the tangent of ar.
doubleMath.toRadians(d) Returns d (angle in degrees)
converted to radians.
doubleMath.toDegrees(ar) Returns ar (angle in radians)
converted to degrees.
Exponential Methods
The two basic functions for logarithms and power are available. These both use the base e (Math.E) as is the usual case in mathematics.
doubleMath.exp(d) Returns e (2.71...)
to the power d.
doubleMath.pow(d1, d2) Returns d1d2.
doubleMath.log(d) Returns the logarithm
of d to base e.
Misc Methods
doubleMath.sqrt(d) Returns the square
root of d.
tMath.abs(x) Returns absolute value
of x with same type
as the parameter: int,
 long, float, or double.
tMath.max(x, y) Returns maximum of x
 and y with same type
as the parameter: int,
 long, float, or double.
tMath.min(x, y) Returns minimum of x
and y with same type
as the parameter: int,
 long, float, or double.
Integer Related Methods
The following methods translate floating point values to integer values, altho these values may still be stored in a double.
doubleMath.floor(d) Returns the closest
integer-valued
 double which is equal
to or less than d.
doubleMath.ceil(d) Returns the closest
integer-valued
 double which is equal
 to or greater than d.
doubleMath.rint(d) Returns the closest
 integer-valued
double to d.
longMath.round(d) Returns the long
which is closest
in value to the
double d.
intMath.round(f) Returns the int
which
 is closest in value
 to the float f.
Random Numbers
For significantly more control over random number generation use the java.util.Random class (see below).
doubleMath.random() Returns a number x in the range, 0.0 <= x < 1.0.
java.util.Random Class
The java.util.Random class provides more flexible ways to generate uniformly distributed random numbers, providing easy generation of types other than double, as well as providing a Gaussian distribution.
Random Constructors
It's necessary to construct a Random object.
Randomnew Random(); Uses time in milliseconds as the seed.
Randomnew Random(long seed); Uses the provided seed for testing purposes.
Random Methods
All methods return a uniform distribution of values, except nextGaussian(). Assume r is a Random object..
intr.nextInt(int n) Returns random int >= 0 and < n.
intr.nextInt() Returns random int (full range).
longr.nextLong() Returns random long (full range).
floatr.nextFloat() Returns random float >=0.0 and < 1.0.
doubler.nextDouble() Returns random double >=0.0 and < 1.0.
booleanr.nextBoolean() Returns random boolean (true or false).
doubler.nextGaussian() Returns random double with mean 0.0 and standard deviation 1.0.

Other math libraries

I don't keep track of math libraries, but I'll add links below as I run across them. I have no idea if these are good or bad.

Copyright 2005 Fred Swartz
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