写的比较简单，只是实现了基本要求

package collectionstringlist_sort;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
//生成随机字符串
public class Test {
    public String getrandomString(int length){
        String base="abcdefghijklmnopqrstuvwxyz0123456789";
        Random random=new Random();
        StringBuffer sb=new StringBuffer();
        for(int i=0;i<length;i++){
            int number=random.nextInt(base.length());
            sb.append(base.charAt(number));
        }
        return sb.toString();
    }
    public static void main(String[] args) {
        List<String> stu=new ArrayList<String>();
        Test test=new Test();
        int length;
        Random random=new Random();
        String st;
        for(int j=0;j<10;j++){
            do{
                length= (int)(random.nextDouble()*10);
                st=test.getrandomString(length);

            }while(stu.contains(st));
            stu.add(st);
            System.out.println("成功添加字符串："+st);
        }
        System.out.println("-----排序前------");
        for (String string : stu) {
            System.out.println("元素：" + string);
        }
        System.out.println("----排序后-----");
        Collections.sort(stu);
        for (String string : stu) {
            System.out.println("元素：" + string);
        }
    }

}