Why Do I Keep Getting the Same Random Numbers in Java When Using a Seed?

Java Random Number Generation with a Seed: Debugging Identical Output

In Java, the Random class provides a way to generate pseudorandom numbers. By specifying a seed as an argument, it is possible to control the sequence of numbers generated. However, an issue arises when the same seed is repeatedly used, resulting in identical sequences of numbers.

Understanding Pseudorandom Number Generation and Seeds

A pseudorandom number generator (PRNG) is an algorithm that generates a sequence of numbers that appears random but is actually determined by a small set of initial values, known as the seed. By specifying a seed, the PRNG produces the same sequence of numbers every time.

Adjusting Code to Generate Varied Sequences

To resolve the issue of identical output, it is necessary to understand how seeds function in PRNGs. In Java, when calling the Random class with a seed argument, it retains the same state for future calls, leading to the same sequence of numbers.

To generate varied sequences, it is recommended to call the zero-argument constructor of Random, which uses the system nanotime as a seed. This ensures that a different seed is used each time the method is called.

Code Correction

The following corrected Java code uses the zero-argument constructor to generate varying sequences of random numbers:

private Random generator = new Random();

double randomGenerator() {
    return generator.nextDouble() * 0.5;
}

By moving the Random instance outside the method and using the system nanotime as a seed, this code eliminates the issue of identical output and generates different sequences of random numbers.

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