生成随机字符串的代码来自百度

package com.imooc.collection;

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

public class CollectionsTest {

    public static String getRandomString(int length) {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";//含有字符和数字的字符串
        Random random = new Random();//随机类初始化
        StringBuffer sb = new StringBuffer();//StringBuffer类生成，为了拼接字符串

        for (int i = 0; i < length; ++i) {
            int number = random.nextInt(62);// [0,62)

            sb.append(str.charAt(number));
        }
        return sb.toString();
    }

    public static void main(String[] args) {

        CollectionsTest ct=new CollectionsTest();
        List<String>  stringList=new ArrayList<String>();
        Random random=new Random();

        String k;

        for(int i=0;i<10;i++){
            do{
                int result=random.nextInt(10)+1;
                k=ct.getRandomString(result);}while(
                    stringList.contains(k));
            stringList.add(k);

        }

        System.out.println("----------before------------");
        for(String string:stringList){
            System.out.println(string);
        }
        System.out.println("---------------after------------------");
        Collections.sort(stringList);
        for(String string:stringList){
            System.out.println(string);
        }

    }

}