How to generate “random” but also “unique” numbers?

Question

How are random numbers generated.? How do languages such as java etc generate random numbers, especially how it is done for GUIDs.? i found that algorithms like Pseudorandomnumb

Answer 1

Specifically regarding Java:

• java.util.Random uses a linear congruential generator, which is not very good
• java.util.UUID#randomUUID() uses java.security.SecureRandom, an interface for a variety of cryptographically secure RNGs - the default is based on SHA-1, I believe.
• UUIDs/GUIDs are not necessarily random
• It's easy to find implementations of RNGs on the net that are much better than java.util.Random, such as the Mersenne Twister or multiply-with-carry