第一次看完课程写了作业，希望以后能越学越好。写的比较简单，后面会慢慢完善的。如果有幸能获得网友的指正，不胜感激！

package com.imooc.collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

/**
 * Created by LinHongwei on 2017/9/14.
 */
public class useSort {

    public void test(){
        List<String> list=new ArrayList<String>();
        Random random= new Random();
        String str="";
        String c = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
        System.out.println("~~~~~~~排序前~~~~~~~");
        for(int i=0;i<10;i++){
            do{
                int len=random.nextInt(10)+1;
                str="";
                for(int j=0;j<len;j++){
                    char ch=c.charAt(random.nextInt(c.length()));
                    str=str+ch;
                }
            }while(list.contains(str));
            list.add(str);
            System.out.println("添加元素："+str);
        }
        Collections.sort(list);
        System.out.println("~~~~~~~排序后~~~~~~~");
        for(int i=0;i<10;i++){
            System.out.println("元素："+list.get(i));
        }
    }

    public static void main(String[] args)
    {
        useSort a=new useSort();
        a.test();
    }
}