Java random numbers using a seed

Question

This is my code to generate random numbers using a seed as an argument   double randomGenerator long seed        Random generator   new Random seed       double num   generator nextDouble      0 5        return num      Every time I give a seed and try to generate 100 numbers  they all are the same  How can I fix this

User · Answer

The easy way is to use   Random rand   new Random System currentTimeMillis       This is the best way to generate Random numbers

User · Answer

Several of the examples here create a new Random instance  but this is unnecessary  There is also no reason to use synchronized as one solution does  Instead  take advantage of the methods on the ThreadLocalRandom class   double randomGenerator         return ThreadLocalRandom current   nextDouble 0 5

User · Answer

You shouldn t be creating a new Random in method scope   Make it a class member   public class Foo      private Random random      public Foo            this System currentTimeMillis              public Foo long seed           this random   new Random seed            public synchronized double getNext             return generator nextDouble             This is only an example   I don t think wrapping Random this way adds any value   Put it in a class of yours that is using it

User · Answer

If you re giving the same seed  that s normal  That s an important feature allowing tests   Check this to understand pseudo random generation and seeds    Pseudorandom number generator      A pseudorandom number generator  PRNG   also known as a deterministic   random bit generator DRBG  is an algorithm for generating a sequence   of numbers that approximates the properties of random numbers  The   sequence is not truly random in that it is completely determined by   a relatively small set of initial values  called the PRNG s state    which includes a truly random seed    If you want to have different sequences  the usual case when not tuning or debugging the algorithm   you should call the zero argument constructor which uses the nanoTime to try to get a different seed every time  This Random instance should of course be kept outside of your method   Your code should probably be like this   private Random generator   new Random    double randomGenerator         return generator nextDouble   0 5

User · Answer

If you d want to generate multiple numbers using one seed you can do something like this   public double   GenerateNumbers long seed  int amount        double   randomList   new double amount       for  int i 0 i lt amount i              Random generator   new Random seed           randomList i    Math abs  double   generator nextLong     0 001    10000           seed--            return randomList      It will display the same list if you use the same seed

User · Answer

Problem is that you seed the random generator again  Every time you seed it the initial state of the random number generator gets reset and the first random number you generate will be the first random number after the initial state

User · Answer

That s the principle of a Pseudo-RNG  The numbers are not really random  They are generated using a deterministic algorithm  but depending on the seed  the sequence of generated numbers vary  Since you always use the same seed  you always get the same sequence

[java] Java random numbers using a seed

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