统计字符串String中每个字符出现的次数

import java.util.HashMap;
import java.util.Set;

/**
 * 统计字符串String中每个字符出现的次数
 * 
 * @author lilongping
 * @version [2012-6-28]
 */
public class HashMapTest
{
    public HashMap<Object, Integer> getHashMap(String str)
    {
        HashMap<Object, Integer> hashMap = new HashMap<Object, Integer>();
        for (int i = 0; i < str.length(); i++)
        {
            char ch = str.charAt(i);
            // 第一次循环
            if (hashMap.isEmpty())
            {
                hashMap.put(ch, 1);
            }
            else
            {
                // 如果第二次取出的值，已经存在hashMap,则增加value值
                if (hashMap.containsKey(ch))
                {
                    Integer value = hashMap.get(ch);
                    hashMap.put(ch, value + 1);
                }
                else
                {
                    hashMap.put(ch, 1);
                }
            }
        }
        return hashMap;
    }
    
    public void printHashMap(HashMap<Object, Integer> hashMap)
    {
        Set<Object> keySet = hashMap.keySet();
        for (Object object : keySet)
        {
            System.out.println("key:" + object.toString() + ", value:"
                    + hashMap.get(object));
        }
    }
    
    public static void main(String[] args)
    {
        String str = "aaaabbbbccccdddddaaaabbbbbcccccddddd";
        HashMap<Object, Integer> hashMap = new Test().getHashMap(str);
        new Test().printHashMap(hashMap);
    }
}