双色球问题~高手请指教

package basic.day05;import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;public class DoubleBall { /**
 * 雙色球
 */
public static void main(String[] args) {
String[] redBall = {"01","02","03","04","05","06","07","08","09",
"11","12","13","14","15","16","17","18","19",
"21","22","23","24","25","26","27","28","29",
"30","31","32","33"};
String[] buleBall = {"01","02","03","04","05","06","07","08","09",
"11","12","13","14","15","16"};
boolean[] labelBall = new boolean[33];
Random ra = new Random();
Scanner console = new Scanner(System.in);
System.out.print("输入所买双色球的注数：");
int n = console.nextInt();
for(int i = 0; i < n; i++){
int s = ra.nextInt(16);
String[] ball = choose(redBall,labelBall);
System.out.print("电脑随机出红蓝球为：");
Arrays.sort(ball);
System.out.print(Arrays.toString(ball));
System.out.println("\t["+buleBall[s]+"]");
}

}
public static String[] choose(String[] redBall, boolean[] labelBall ){
String[] newBall = {};
Random ra = new Random();
int s;
for(int i = 0; i < 6; i++){

do{
 s = ra.nextInt(33);
}while(labelBall[s] == true);
labelBall[s] = true;
newBall = Arrays.copyOf(newBall, newBall.length + 1);
newBall[newBall.length-1] = redBall[s];
}
return newBall;
}
}我看了好久 还是不知道那错了。 为什么有时候运行的时候可以 有的时候运行就报错了。 请高手指点。 请说清楚。不要说“越界”两个字就行了。  谢谢。。