public class Test { public static void main(String[] args) {
System.out.println(random16());
}
public static StringBuilder random16() {
StringBuilder s = new StringBuilder();
Random random = new Random();
Integer ints; for (int i = 0; i < 4; i++) {
ints = (random.nextInt(10000) + 100000) % 10000; // System.out.println(ints.toString()); s.append(ints.toString());
} return s;
}