java.lang.Object  +java.util.Random
An instance of this class is used to generate a stream of pseudorandom numbers. The class uses a 48bit seed, which is modified using a linear congruential formula. (See Donald Knuth, The Art of Computer Programming, Volume 2, Section 3.2.1.)
If two instances of Random
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 order to
guarantee this property, particular 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
portability of Java code. However, subclasses of class Random
are permitted to use other algorithms, so long as they adhere to the
general contracts for all the methods.
The algorithms implemented by class Random use a protected utility method that on each invocation can supply up to 32 pseudorandomly generated bits.
Constructor Summary  
Random()
Creates a new random number generator. 

Random(long seed)
Creates a new random number generator using a single long seed:

Method Summary  
protected int 
next(int bits)
Generates the next pseudorandom number. 
int 
nextInt()
Returns the next pseudorandom, uniformly distributed int
value from this random number generator's sequence. 
long 
nextLong()
Returns the next pseudorandom, uniformly distributed long
value from this random number generator's sequence. 
void 
setSeed(long seed)
Sets the seed of this random number generator using a single long seed. 
Methods inherited from class java.lang.Object 
equals,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait 
Constructor Detail 
public Random()
public Random() { this(System.currentTimeMillis()); }
System.currentTimeMillis()
public Random(long seed)
long
seed:
Used by method next to hold the state of the pseudorandom number generator.public Random(long seed) { setSeed(seed); }
seed
 the initial seed.setSeed(long)
Method Detail 
public void setSeed(long seed)
long
seed. The general contract of setSeed
is that it alters the state of this random number generator
object so as to be in exactly the same state as if it had just
been created with the argument seed as a seed. The method
setSeed is implemented by class Random as follows:
The implementation of setSeed by class Random happens to use only 48 bits of the given seed. In general, however, an overriding method may use all 64 bits of the long argument as a seed value.synchronized public void setSeed(long seed) { this.seed = (seed ^ 0x5DEECE66DL) & ((1L << 48)  1); }
seed
 the initial seed.protected int next(int bits)
The general contract of next is that it returns an int value and if the argument bits is between 1 and 32 (inclusive), then that many loworder bits of the returned value will be (approximately) independently chosen bit values, each of which is (approximately) equally likely to be 0 or 1. The method next is implemented by class Random as follows:
This is a linear congruential pseudorandom number generator, as defined by D. H. Lehmer and described by Donald E. Knuth in The Art of Computer Programming, Volume 2: Seminumerical Algorithms, section 3.2.1.synchronized protected int next(int bits) { seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48)  1); return (int)(seed >>> (48  bits)); }
bits
 random bitspublic int nextInt()
int
value from this random number generator's sequence. The general
contract of nextInt is that one int value is
pseudorandomly generated and returned. All 2^{32
} possible int values are produced with
(approximately) equal probability. The method nextInt is
implemented by class Random as follows:
public int nextInt() { return next(32); }
int
value from this random number generator's sequence.public long nextLong()
long
value from this random number generator's sequence. The general
contract of nextLong is that one long value is pseudorandomly
generated and returned. All 2^{64}
possible long values are produced with (approximately) equal
probability. The method nextLong is implemented by class
Random as follows:
public long nextLong() { return ((long)next(32) << 32) + next(32); }
long
value from this random number generator's sequence.