Random Number list

Question

Lo peeps, I have a small problem, i'm trying to create a random number generator and create a list of size current_size. The code also generates the random number from zero to current_size. The following code seems to work correctly in generating a random number, but it doesn't create a list of random numbers, instead it creates a list of the same random number!!! Does anyone have any ideas?
import java.util.*;       // needed for Random
public class ListByArray
    private     int           current_size;
    private     String[]      data;
    private final int        default_max_size = 4096;
    public int createRandomList(String string_size)
        int i;
        int j;
        if(!isIntString(string_size)) {
            return 0;
        else {
            Integer size = Integer.valueOf(string_size);
            current_size = size.intValue();
        for(i=0; i<current_size; i++) {
            Random R = new Random();
            j = (int)(R.nextFloat()*current_size);
            data[i] = Integer.toString(j);
        return current_size;
    } //end createRandomList
} //end classIt's manly the for loop which I'm wondering about because I know the rest of the code works!!!.

Answer 1

That line creates a new pseudo random number generator with the current time (in milliseconds) as a seed. When you call r.nextFloat you don't actually get a random number but a number that is a function of the last number generated, or, if there are no numbers yet generated, of the seed (that's why they call them pseudo random number generators). So the sequence you get is totally dependent on the seed. Your loop seems to be passed so fast that the time in milliseconds doesn't change during it, with the result that you have many generators with the exact same seed and will produce the exact same sequence of numbers... and you use only the first number of each sequence.
But if you move the line outside the loop you'll have only one RNG that is seeded only once.
More info on RNGs: http://directory.google.com/Top/Computers/Algorithms/Pseudorandom_Numbers/