21.9

java.util.Random

THE PACKAGE JAVA.UTIL

21.9 The Class

java.util.Random

Oh, many a shaft at random sent

Finds mark the archer little meant!

And many a word at random spoken

May soothe, or wound, a heart that's broken!

 Sir Walter Scott,

The Lady of the Lake

, Canto V, stanza 18

Each instance of class

Random

 serves as a separate, independent pseudorandom

generator of primitive values.

public class Random {

protected long seed;

protected double nextNextGaussian;

protected boolean haveNextNextGaussian = false;

public Random();

public Random(long seed);

public void setSeed(long seed);

protected int next(int bits);

public int nextInt();

public long nextLong();

public float nextFloat();

public double nextDouble();

public double nextGaussian();

}

If two

Random

 objects are created with the same seed and the same sequence

of method calls is made for each, they will generate and return identical sequences

of numbers in all Java implementations. In order to guarantee this property, partic 

ular algorithms are specified for the class

Random

. Java implementations must use

all the algorithms shown here for the class

Random

, for the sake of absolute porta 

bility of Java code. However, subclasses of class

Random

 are permitted use other

algorithms, so long as they adhere to the general contracts for all the methods.

The algorithms implemented by class

Random

 use three state variables, which

are

protected

. They also use a

protected

 utility method that on each invocation

can supply up to up to 32 pseudorandomly generated bits.

21.9.1

protected long seed;

A variable used by method

next

 ( 21.9.7) to hold the state of the pseudorandom

number generator.

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