Bit Fields 位域型
Two objects that are not bit-fields may have the same address if one is a subobject of the other, or if at least one is a base class subobject of zero size and they are of different types;
不属于位域的两个对象可能拥有相同的地址（如果一个对象是另一个对象的子对象，或者至少有一个是空的基类子对象，并且他们的类型不同）； 否则，他们应该在不同的地址上。
That is a bit larger than three soccer fields.
这比三个足球场还要大一点。
It is a commonly held belief that you do not need to acquire a lock to simply read an object's fields, especially since the JLS guarantees that 32-bit reads will be atomic.
有一种普遍的观点是，如果只是要读一个对象的字段，不需要请求加锁，尤其是在JLS保证了32位读操作的原子性的情况下，它更是如此。
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