Java計算字符在字符串內出現的次數

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;

public class CountAppears {
	public static void main(String[] args) {
		String tmp = "";// 字符串
		ArrayList<Map.Entry<String, Integer>> ls = new ArrayList<Map.Entry<String, Integer>>(
				count(tmp, new HashMap<String, Integer>()).entrySet());
		Collections.sort(ls, new Comparator<Map.Entry<String, Integer>>() {
			public int compare(Map.Entry<String, Integer> obj1,
					Map.Entry<String, Integer> obj2) {
				return (obj2.getValue() - obj1.getValue());
			}
		});
		for (Map.Entry<String, Integer> e : ls) {
			System.out.println(e.getKey() + "出現次數" + e.getValue());
		}
	}

	public static Map<String, Integer> count(String str, Map<String, Integer> rs) {
		if (str == null || str.equals(""))
			return rs;
		int isize = str.length();
		String tempStr = str.substring(0, 1);
		str = str.replaceAll(tempStr, "");
		int tempStrSize = str.length();
		rs.put(tempStr, isize - tempStrSize);
		return count(str, rs);
	}
}