Counting sheep...

public class Counter {
  public int countSheeps(Boolean[] arrayOfSheeps) {
    int counter = 0;
    for (Boolean sheep : arrayOfSheeps) {
      if (sheep != null && sheep) {
        counter++;
      }
    }
    return counter;
  }
}

刚开始，用的if (sheep),报错java.lang.NullPointerException空指针异常。
当一个对象的值为空时，并且没有判断为空的情况。可以试着把下面的代码前加一行代码：
if(rb!=null);