Java入门第三季 6-5练习 随机字符串

 import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
public class CollectionsTest {
public void testSort(){
    List<String> stringsList = new ArrayList<String>();
    Random random1 = new Random();
    String f1 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    //创建一个内容可变的字符串对象
    StringBuilder f2 = new StringBuilder();
    for(int i=0;i<10;i++){

     do{
/*
* 这里用9+1是因为如果随机到0还可以加1，将0避免掉，不然0个字符串无法与其它字符比较    
*/
         int k = random1.nextInt(9)+1;
//如果新创建的随机字符串与之前的重复了，则清空该字符串，重新来过        
         f2 = new StringBuilder();
       for(int j=0;j<k;j++){
//charAt(int index)获取字符串中指定位置的字符
           f2.append(f1.charAt(random1.nextInt(f1.length())));
       }
     }while(stringsList.contains(f2.toString()));
        System.out.println("将要添加字符串：'" + f2.toString() + "'");
        stringsList.add(f2.toString());
    }
    System.out.println("---------------排序前--------------");
    for (String string : stringsList) {
        System.out.println("元素：" + string);
    }
    Collections.sort(stringsList);
    System.out.println("---------------排序后--------------");
    for (String string : stringsList) {
        System.out.println("元素：" + string);
    }
}   
public static void main(String[] args) {
    // TODO Auto-generated method stub
 CollectionsTest ct = new CollectionsTest();

 ct.testSort();
}

}