entityMap|blocks|key|avt1v|text|为什么这需要是暂时的？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|79no8|50gpd|它之所以这样做，是因为它提供了自定义|dc65s|和|3f2f|方法在序列化方面比默认方法做得更好。具体地说，writeObject方法只写入元素的大小和序列。这避免了序列化私有数组对象，1)有自己的头和开销，2)通常填充|8mpml|s。节省的空间可以是显著的。|7cmj9|为什么这个类不能序列化？|5iqgv|epmco|The+The+The|bfe3t|类作为一个整体可以是serialized1。The+The+The|b6etd|可以直接序列化，但他们选择将其标记为|4pds9|以另一种方式实现序列化。|8ca1i|1-实际上，这取决于元素的运行时类型。例如，如果您尝试序列化|f8bj8|包含|7ckh2|引用，那么您将得到第一个非空引用的运行时异常。^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|12|9|@]|A|@]|B|$]]|$2|C|4|-4|6|7|8|13|9|@]|A|@]|B|$]]|$2|D|4|E|6|7|8|14|9|@]|A|@]|B|$]]|$2|F|4|G|6|7|8|15|9|@]|A|@]|B|$]]|$2|H|4|I|6|7|8|16|9|@]|A|@]|B|$]]|$2|J|4|K|6|7|8|17|9|@]|A|@]|B|$]]|$2|L|4|M|6|7|8|18|9|@]|A|@]|B|$]]|$2|N|4|-4|6|7|8|19|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|1A|9|@]|A|@]|B|$]]|$2|Q|4|R|6|7|8|1B|9|@]|A|@]|B|$]]|$2|S|4|T|6|7|8|1C|9|@]|A|@]|B|$]]|$2|U|4|V|6|7|8|1D|9|@]|A|@]|B|$]]|$2|W|4|X|6|7|8|1E|9|@]|A|@]|B|$]]|$2|Y|4|Z|6|7|8|1F|9|@]|A|@]|B|$]]|$2|10|4|11|6|7|8|1G|9|@]|A|@]|B|$]]]]

<blockquote>
Why does this need to be transient?
</blockquote>
It does this because it provides custom <code>readObject</code> and <code>writeObject</code> methods that do a better job of serialization than the default. Specifically, the writeObject method writes just the size and the sequence of elements. This avoids serializing the private array object which 1) has its own header and overheads, and 2) is typically padded with <code>null</code>s. The space saving can be significant.
<blockquote>
Why can't this class be serialized?
</blockquote>
The <code>ArrayList</code> class as a whole can be serialized1. The <code>Object[]</code> could be serialized directly, but they chose to mark it as <code>transient</code> implement the serialization another way.
<hr />
1 - Actually, this depends on the elements' runtime types. For example, if you attempted to serialize an <code>ArrayList</code> containing <code>Thread</code> references, then you would get a runtime exception for the first non-null reference.

entityMap|blocks|key|8cnfi|text|因为它实现了显式序列化。参见ArrayList#writeObject。|type|unstyled|depth|inlineStyleRanges|entityRanges|data^0^^$0|$]|1|@$2|3|4|5|6|7|8|C|9|@]|A|@]|B|$]]]]

Because it implements explicit serialization. See ArrayList#writeObject.

entityMap|blocks|key|4vu4n|text|实现|type|unstyled|depth|inlineStyleRanges|entityRanges|data|dmgab|，所以|a4599|可以|8kn90|被序列化，这就是为什么私有支持数组|aoh0k|，因此它不会与类中的其他数据一起序列化，因为所有数据都由|ae8rd|%25s|76v2h|和|2c4lj|方法。^0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|Q|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|R|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|S|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|T|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|U|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|V|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|W|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|X|9|@]|A|@]|B|$]]]]

<code>ArrayList</code> implements <code>Serializable</code>, so it can be serialized, that's exactly why the private backing array is <code>transient</code>, so it is not serialized along with other data in the class, since all is handled by <code>ArrayList</code>'s <code>writeObject</code> and <code>readObject</code> methods.

entityMap|blocks|key|dkhfp|text|它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|7mr3f|可以|e7gv9|被序列化；|1k1qn|类只负责自己的事情，而不是使用默认机制。看看|8cmq1|和|74a87|方法，这些方法是标准序列化机制的一部分。|de3vh|如果你看一下源代码，你会发现|lvla|不保存支持数组。相反，它一次序列化一个元素(包括null值)，直到|64fie|限制。这避免了序列化数组的开销，特别是在数组末尾的任何未使用的插槽。在反序列化时，将创建所需最小大小的新支持数组|97hlf|..。^0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|U|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|V|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|W|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|X|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|Y|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|Z|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|10|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|11|9|@]|A|@]|B|$]]|$2|Q|4|R|6|7|8|12|9|@]|A|@]|B|$]]|$2|S|4|T|6|7|8|13|9|@]|A|@]|B|$]]]]

It can be serialized; the <code>ArrayList</code> class just takes care of things itself, rather than using the default mechanism. Look at the <code>writeObject()</code> and <code>readObject()</code> methods in that class, which are part of the standard serialization mechanism.

If you look at the source, you see that <code>writeObject()</code> does not save the backing array. Instead, it serializes the elements (including null values) one at a time up to the <code>size()</code> limit. This avoids the overheads of serializing the array, and especially any unused slots at the end of the array. On deserialization, a new backing array of the minimum required size is created by <code>readObject()</code>.

entityMap|blocks|key|1aq80|text|该变量不可序列化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|8prqt|如果变量不可序列化，则序列化机制将在尝试序列化变量时抛出异常。为了避免这种情况，您可以将变量声明为瞬态变量。|6vn78|该变量是多余的。|bnvmu|假设实例缓存了计算结果。在本地，我们可能希望存储计算结果，以便节省一些处理器时间。但是当我们通过网络发送对象时，我们可能更担心消耗带宽，从而丢弃缓存的计算，因为我们总是可以在以后重新生成它。|et7bu|链接：|9crk5|http://onjava.com/pub/a/onjava/excerpt/JavaRMI|58jd4|_|e1785|10/index.html?page=3^0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|Q|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|R|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|S|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|T|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|U|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|V|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|W|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|X|9|@]|A|@]|B|$]]]]

The variable isn't serializable.

<ul>
<li>If the variable isn't serializable, then the serialization mechanism will throw an exception when it tries to serialize the variable. To avoid this, you can declare the variable to be transient.</li>
</ul>

The variable is redundant.

<ul>
<li>Suppose that the instance caches the result of a computation. Locally, we might want
to store the result of the computation, in order to save some processor time. But 
when we send the object over the wire, we might worry more about consuming bandwidth
and thus discard the cached computation since we can always regenerate it later on.</li>
</ul>

link: <a href="http://onjava.com/pub/a/onjava/excerpt/JavaRMI_10/index.html?page=3" rel="nofollow noreferrer">http://onjava.com/pub/a/onjava/excerpt/JavaRMI_10/index.html?page=3</a>

entityMap|blocks|key|33la9|text|根据上面Stephen+C的回答，我想纠正他关于使用瞬态的注意事项，在|type|unstyled|depth|inlineStyleRanges|entityRanges|data|e1f72|对于可读性而言，在他的答案下，这可能是更好的注释，但我还没有这种能力！|aebg8|当字段被标记为|c9pk8|对于可读性很有帮助，由于习惯的原因，它也是必要的。|dtdt|和|5de2u|方法调用|6mub1|%25s|k3cp|b8pj3|%25s|4gv2t|方法。这些方法将处理所有未标记的字段的序列化这一繁琐的工作|eo50t|(例如|dv9gp|)。|7p67d|请参阅的源代码|eqlt4|有关更多详细信息，请单击此处：|bmb59|https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/io/ObjectOutputStream.java#L431^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|13|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|14|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|15|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|16|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|17|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|18|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|19|9|@]|A|@]|B|$]]|$2|O|4|J|6|7|8|1A|9|@]|A|@]|B|$]]|$2|P|4|Q|6|7|8|1B|9|@]|A|@]|B|$]]|$2|R|4|S|6|7|8|1C|9|@]|A|@]|B|$]]|$2|T|4|U|6|7|8|1D|9|@]|A|@]|B|$]]|$2|V|4|W|6|7|8|1E|9|@]|A|@]|B|$]]|$2|X|4|Y|6|7|8|1F|9|@]|A|@]|B|$]]|$2|Z|4|10|6|7|8|1G|9|@]|A|@]|B|$]]|$2|11|4|12|6|7|8|1H|9|@]|A|@]|B|$]]]]

Extending on Stephen C's answer above, I would like to correct his note about transient being used, in <code>ArrayLists</code>'s case, for readability. This may be better as a comment under his answer but I don't have that ability yet!

While the field being marked as <code>transient</code> is helpful for readability, it is also necessary due to the custom <code>readObject</code> and <code>writeObject</code> methods calling <code>java.io.ObjectInputStream</code>'s <code>defaultReadObject</code> and <code>java.io.ObjectOutputStream</code>'s <code>defaultWriteObject</code> methods respectively. These methods will do the dirty work of handling serializiation of all the fields not marked <code>transient</code> (e.g. <code>size</code>).

See the source code for <code>ObjectOutputStream</code> for more details here: <a href="https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/io/ObjectOutputStream.java#L431" rel="nofollow noreferrer">https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/io/ObjectOutputStream.java#L431</a>

I was reading the source of Java's ArrayList and I came across its backing array declaration:

<pre><code>private transient Object[] elementData;
</code></pre>

Why does this need to be transient? Why can't this class be serialized?

Thanks for the help!

Why does ArrayList use transient storage?

Java

 我正在阅读Java的ArrayList的源代码，我偶然发现了它的后端数组声明： private transient Object[] elementData; 为什么这需要是暂时的？为什么这个类不能序列化？ 谢谢你的帮助！

问为什么ArrayList使用瞬态存储？
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