怎么随机产生车牌号，求解释

Question

不知道怎么写，想了一下午，不同类型的怎么弄到一块去。数字和字母，怎么随机放一块？纠结死了

Answer 1

  int count = 0;
    String carNo = "";
    while(count<5){
    long time = System.currentTimeMillis();
    Random random = new Random(time);
    String str = "abcdefghijklmnopqrstuvwxyz";
    char str2 = str.charAt(random.nextInt(26));
    int num = random.nextInt(10);
    //字母与数字的概率相同
    if (num<5) {
        carNo += num;
    }
    else {
        carNo += str2;
    }
    count++;
    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    }
    System.out.println("车牌号是："+carNo);