// collections/Statistics.java // (c)2016 MindView LLC: see Copyright.txt // We make no guarantees that this code is fit for any purpose. // Visit http://mindviewinc.com/Books/OnJava/ for more book information. // Simple demonstration of HashMap import java.util.*; public class Statistics { public static void main(String[] args) { Random rand = new Random(47); Map m = new HashMap<>(); for(int i = 0; i < 10000; i++) { // Produce a number between 0 and 20: int r = rand.nextInt(20); Integer freq = m.get(r); // (1) m.put(r, freq == null ? 1 : freq + 1); } System.out.println(m); } } /* Output: {0=481, 1=502, 2=489, 3=508, 4=481, 5=503, 6=519, 7=471, 8=468, 9=549, 10=513, 11=531, 12=521, 13=506, 14=477, 15=497, 16=533, 17=509, 18=478, 19=464} */