# V6109. Potentially predictable seed is used in pseudo-random number generator.

This diagnostic rule detects cases where a pseudo-random number generator is used. It may result in insufficient randomness or predictability of the generated number.

Case 1.

Creating a new object of the 'Random' type every time a random value is required. This is inefficient and may result in creating numbers that are not random enough, depending on the JDK.

Here is an example:

    public void test() {
      Random rnd = new Random();
    }

For a more efficient and random distribution, create an instance of the 'Random' class, save it, and reuse it.

    static Random rnd = new Random();

    public void test() {
      int i = rnd.nextInt();
    }

Case 2.

The analyzer detected suspicious code that initializes the pseudo-random number generator with a constant value.

    public void test() {
      Random rnd = new Random(4040);
    }

Numbers generated by such a generator are predictable — they are repeated every time the program runs. To avoid this, do not use a constant number. For example, you can use the current system time instead:

    static Random rnd = new Random(System.currentTimeMillis());

    public void test() {
      int i = rnd.nextInt();
    }

This diagnostic is classified as:

CWE-336 CWE-337