2016/4/14

package com.mashibing;

import java.util.HashMap;
import java.util.Map;

/**
 * Created by jl on 2016/4/14.
 */
public class TestArgsWords {
    private static final int ONE = 1;

    public static void main(String[] args) {
        Map m = new HashMap();
        for(int i =0;i<args.length;i++){
            int freq = (Integer)m.get(args[i]);
            m.put(args[i],(freq==0? ONE : freq+1));
        }
        System.out.println(m.size()+" distinct words detected:");
        System.out.println(m);
    }
}

运行结果

 
 

  
  Exception in thread "main" java.lang.NullPointerException
 at com.mashibing.TestArgsWords.main(TestArgsWords.java:15)

 
 
 
 


 
 
 
 

  
  Process finished with exit code 1
 
 
 
 


 
 
 
 

  
  第十五行出现了空指针异常，改成如下
  
  
int freq = (Integer)m.get(args[i])==null?0:(Integer)m.get(args[i]);