java Map输出字符串中字母出现的次数

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/*
 * Map练习，输出字符串中字母出现的次数
 */
public class MapDemo {

	public static void main(String[] args) {
		System.out.println(method("aa+b-c,d.dhjjb"));
	}
	
	public static String method(String str) {
		char[] chs = str.toCharArray();
		Map map = new TreeMap();
		for(int i=0;i='a' && chs[i]<='z' || chs[i]>='A' && chs[i]<='Z'))
				continue;
			Integer value = map.get(chs[i]);
			if(value==null) {
				map.put(chs[i], 1);
			} else {
				map.put(chs[i], value + 1);
			}
		}
		//System.out.println(map);
		StringBuilder sb = new StringBuilder();
		Set> entrySet = map.entrySet();
		for(Iterator> it = entrySet.iterator();it.hasNext();) {
			Map.Entry me = it.next();
			Character key = me.getKey();
			Integer value = me.getValue();
			sb.append(key + "(" + value + ") ");
		}
		return sb.toString();
	}
	
}