java怎么实现统计一个字符串中字符出现的次数

 1 import java.util.HashMap;
 2 import java.util.Iterator;
 3 import java.util.Map;
 4 
 5 public class TestCompress {
 6     
 7     public static void main(String[] args) {
 8         String str = "aaabbbcccdfb";
 9         compress(str);
10     }
11     
12     public static void compress(String str) {
13         Map<String, Integer> count = new HashMap<String, Integer>();
14         String[] myStrs = str.split("");
15         for (int i = 0; i < myStrs.length; i++) {
16             int totalNum = 1;
17             String currentStr = myStrs[i];
18             if (count.containsKey(currentStr)) {
19                 totalNum = count.get(currentStr) + 1;
20             }
21             count.put(currentStr, totalNum);
22         }
23         int num = count.size();
24         System.out.println("压缩结果");
25         if (num == myStrs.length) {
26             System.out.println("各个字母都不一样，直接返回");
27             System.out.println(str);
28             return;
29         }
30         String result = "";
31         Iterator<Map.Entry<String, Integer>> it = count.entrySet().iterator();
32         while (it.hasNext()) {
33             Map.Entry<String, Integer> entry = it.next();
34             result = result + entry.getKey() + entry.getValue();
35         }
36         System.out.println(result);
37     }
38 }

1 压缩结果
2 a3b4c3d1f1