The RandomGenerator interface is designed to provide a common protocol for objects that generate random or (more typically) pseudorandom sequences of numbers (or Boolean values). Such a sequence may be obtained by either repeatedly invoking a method that returns a single pseudorandomly chosen value, or by invoking a method that returns a stream of pseudorandomly chosen values.

Ideally, given an implicitly or explicitly specified range of values, each value would be chosen independently and uniformly from that range. In practice, one may have to settle for some approximation to independence and uniformity.

In the case of int, long, and boolean values, if there is no explicit specification of range, then the range includes all possible values of the type. In the case of float and double values, first a value is always chosen uniformly from the set of 2^w values between 0.0 (inclusive) and 1.0 (exclusive), where w is Float#PRECISION for float values and Double#PRECISION for double values, such that adjacent values differ by 2^−w (notice that this set is a subset of the set of all representable floating-point values between 0.0 (inclusive) and 1.0 (exclusive)); then if an explicit range was specified, then the chosen number is computationally scaled and translated so as to appear to have been chosen approximately uniformly from that explicit range.

Each method that returns a stream produces a stream of values each of which is chosen in the same manner as for a method that returns a single pseudorandomly chosen value. For example, if r implements RandomGenerator, then the method call r.ints(100) returns a stream of 100 int values. These are not necessarily the exact same values that would have been returned if instead r.nextInt() had been called 100 times; all that is guaranteed is that each value in the stream is chosen in a similar pseudorandom manner from the same range.

Every object that implements the RandomGenerator interface by using a pseudorandom algorithm is assumed to contain a finite amount of state. Using such an object to generate a pseudorandomly chosen value alters its state by computing a new state as a function of the current state, without reference to any information other than the current state. The number of distinct possible states of such an object is called its period. (Some implementations of the RandomGenerator interface may be truly random rather than pseudorandom, for example relying on the statistical behavior of a physical object to derive chosen values. Such implementations do not have a fixed period.)

As a rule, objects that implement the RandomGenerator interface need not be thread-safe. It is recommended that multithreaded applications use either ThreadLocalRandom or (preferably) pseudorandom number generators that implement the SplittableGenerator or JumpableGenerator interface.

Objects that implement RandomGenerator are typically not cryptographically secure. Consider instead using SecureRandom to get a cryptographically secure pseudorandom number generator for use by security-sensitive applications. Note, however, that SecureRandom does implement the RandomGenerator interface, so that instances of SecureRandom may be used interchangeably with other types of pseudorandom generators in applications that do not require a secure generator.

Unless explicit stated otherwise, the use of null for any method argument will cause a NullPointerException.