Problem with random numbers

Question

This is a snippet from a class
public class Cell {
     private int index;  //index of empire
     private int xCoord;  //X coordinate on the grid
     private int yCoord;  //Y coordinate on the grid
     private double solidarity;  //solidarity value of a cell
     private double power;  //power of a cell
     private Random ran;
     public Cell(int i, int x, int y) {
          ran = new Random();
          index = i;
          xCoord = x;
          yCoord = y;
          solidarity = (double)ran.nextInt(100)/100.0;
......I make a couple hundred of these cells when i run the program and at random it seems, every Cell i create ends up having the same exact solidarity value, which really messes up my simulation. It seems to happen once every 5 runs or so. What could be causing this to happen?

Answer 1

In Java 1.4 Random is initalised with the time.
Thus if you create many Random objects at the same time, they will generate the same "random" values.
In Java 5.0 it prevents this behaviour.
In your case the simplest thing to do is to create one Random and share it.
Or you could create your own random seed using i,x,y for example. (thus ensure the random seed is different for each cell)