给定一个字符串数组，按照字典顺序进行从小到大的排序

import java.util.*;

public class Main {
    public static class MyCompara implements Comparator<String> {
        public int compare(String s1, String s2) {
            String tmp1 = s1 + s2;
            String tmp2 = s2 + s1;
            return tmp1.compareTo(s2);
        }
    }
    public static String minString(String[] str) {
        String res = "";
        Arrays.sort(str,new MyCompara());
        for(int i = 0;i < str.length;i++)
            res += str[i];
        return res;
    }
    public static void main(String[] args) {
        System.out.println(minString(new String[] {"ab","ef","cd"}));
    }
}