如果这个指针为空，那么这个信号量就不能被继承。

If this is null, the semaphore cannot be inherited.

youdao

它在两个域中都放置一个空指针来表示空链表，而不是为空链表定义一个单独的类。

Instead of defining a separate class for empty lists, it represents empty lists by putting a null pointer in both fields.

youdao

在许多空指针异常中，真正的错误出现在变量被赋为空值的地方。

In many null-pointer exceptions, the true bug occurs where the variable is actually assigned to null.

youdao