statistics.java

Java编程思想 第九课 全源码

//: c09:Statistics.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// Simple demonstration of HashMap.
import java.util.*;

class Counter { 
  int i = 1; 
  public String toString() { 
    return Integer.toString(i); 
  }
}

class Statistics {
  public static void main(String[] args) {
    HashMap hm = new HashMap();
    for(int i = 0; i < 10000; i++) {
      // Produce a number between 0 and 20:
      Integer r = 
        new Integer((int)(Math.random() * 20));
      if(hm.containsKey(r)){
      //	System.out.print("hm.get(" + r +"): ");
        ((Counter)hm.get(r)).i++;
      }
      else{
 
        hm.put(r, new Counter());
      }
    }
    System.out.println(hm);
  }
} ///:~