statistics.java

thinking in java 书中源码 第四版

//: holding/Statistics.java
// 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<Integer,Integer>();
    for(int i = 0; i < 10000; i++) {
      // Produce a number between 0 and 20:
      int r = rand.nextInt(20);
      Integer freq = m.get(r);
      m.put(r, freq == null ? 1 : freq + 1);
    }
    System.out.println(m);
  }
} /* Output:
{15=497, 4=481, 19=464, 8=468, 11=531, 16=533, 18=478, 3=508, 7=471, 12=521, 17=509, 2=489, 13=506, 9=549, 6=519, 1=502, 14=477, 10=513, 5=503, 0=481}
*///:~