Characteristics of PRNGs

Because PRNGs generate a sequence of values based on an algorithm instead of a “random” physical source, this sequence will eventually restart. The number of values a PRNG generates before it restarts is called a period.

The state cycle of a PRNG consists of the sequence of all possible values a PRNG can generate. The state of a PRNG is the position of the last generated value in its state cycle.

In general, to generate a value, the PRNG bases it on the previously generated value. However, some PRNGs can generate a value many values further down the sequence without calculating any intermediate values. These are called jumpable PRNGs because they could jump far ahead in the sequence of values, usually by a fixed distance, typically 2⁶⁴. A leapable PRNG can jump even further, typically 2¹²⁸ values. An arbitrarily jumpable PRNG can jump to any value in the generated sequence of values.

The java.util.Random Class Compared to Other PRNGs

The java.util.random.RandomGeneratorFactory class enables you to create various PRNGs, many of which are in the jdk.random package. The most significant difference between the PRNGs in jdk.random and the java.util.Random class is that Random has a very short period: only 2⁴⁸ values.