If we now rerun the code to traverse all cars and their sensor readings, we are again confronted with the same problem that we had before, we end up with some leaves of our object graph being null.

如果我们重新运行代码遍历所有的汽车以及它们的感应器读数，我们将遭遇和前面一样的问题，我们获得的对象图表某些叶子节点为空。

youdao

If a pointer pointing to an object not in the graph, then the object is not a reachable object, and then garbage collector sets the slot to null in the short weak reference table.

如果一个指针指向一个不在图中的对象，那么此对象就是一个不可到达的对象，垃圾收集器就将短弱引用表相应的槽置空。

youdao

If a pointer pointing to an object not in the graph, then the object is not a reachable object, and then garbage collector sets the slot to null in the long weak reference table.

如果一个指针指向一个不在图中的对象(注意此时图中已包含Finalize可到达的对象)，那么此对象就是一个不可到达的对象，垃圾收集器就将长弱引用表相应的槽置空。

youdao