Random in java doesn't work right

I'm trying to generate random numbers for the x and y pos of the ball (to put it inside a rectangle), and the random doesn't seem to work right (with numbers, and with parameters)

public Ball createBall(int upper, int lower, int radius){
    Random rand = new Random();
    int temp = lower + radius;
    int temp2 = upper - radius;
    int x = rand.nextInt(600) + 450;
    int y = rand.nextInt(temp2) + temp;
    Ball ball = new Ball(new Point(x,y), radius, Color.BLACK);
    return ball;
}