OnJava8-Examples/collections/Statistics.java

// 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<Integer, Integer> 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}
*/