Why Does My Java Random Number Generator Always Produce the Same Output When I Set a Seed?

Java Random Number Generator: Why Always the Same Output with Set Seed?

In Java, when utilizing the Random class for generating random numbers, it's not uncommon to encounter situations where setting a seed consistently yields the same output. Let's delve into the issue and explore an effective solution.

Consider the following code snippet:

public int random(int i){
    Random randnum = new Random();
    randnum.setSeed(123456789);
    return randnum.nextInt(i);
}

When called multiple times from another class, this method should ideally provide distinct random numbers. However, it consistently returns the same result, such as "5" when invoked with numbers.random(10).

The culprit behind this behavior lies in the creation of a new Random instance within the random method. Each new instance uses a different seed generator, resulting in a predictable sequence of numbers. To rectify this, the Random instance needs to be shared across the entire class.

public class Numbers {
    Random randnum;

    public Numbers() {
        randnum = new Random();
        randnum.setSeed(123456789);
    }

    public int random(int i){
        return randnum.nextInt(i);
    }
}

Now, with the shared Random instance, multiple invocations of the random method will generate genuinely random numbers, even with a set seed. The seed serves as a starting point for the random number generator, ensuring consistency across multiple runs while still maintaining the intended element of randomness.

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