代码

import java.util.*;

/*6.定义一个泛型为String类型的List集合，统计该集合中每个字符
        （注意，不是字符串）出现的次数。例如：集合中有”abc”、”bcd”两个元素，
        程序最终输出结果为：“a = 1,b = 2,c = 2,d = 1”。*/
public class Homework6 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();

        list.add("abc");
        list.add("bcd");

        StringBuffer strs = new StringBuffer();
        for (String s : list){
                strs.append(s);
        }

        char[] chars = strs.toString().toCharArray();

        Map<Character, Integer> map = new TreeMap<>();
        for (int i = 0; i < chars.length; i++) {
            int rate = 1;
            for (int j = 0; j < i; j++) {
                if (chars[i] == chars[j]){
                    rate++;
                }
            }
            map.put(chars[i], rate);
        }

        Set<Map.Entry<Character, Integer>> set = map.entrySet();
        for (Map.Entry<Character, Integer> me : set){
            System.out.println(me.getKey() + "=" + me.getValue());
        }
    }
}