Generating 10 digits unique random number in java

Question

I am trying with below code to generate 10 digits unique random number. As per my req i have to create around 5000 unique numbers(ids). This is not working as expected. It a

Answer 1

This is a utility method for generating a fixed length random number.

    public final static String createRandomNumber(long len) {
    if (len > 18)
        throw new IllegalStateException("To many digits");
    long tLen = (long) Math.pow(10, len - 1) * 9;

    long number = (long) (Math.random() * tLen) + (long) Math.pow(10, len - 1) * 1;

    String tVal = number + "";
    if (tVal.length() != len) {
        throw new IllegalStateException("The random number '" + tVal + "' is not '" + len + "' digits");
    }
    return tVal;
}