为什么Java的基于价值的类不能被序列化？ [英] Why should Java's value-based classes not be serialized?

问题描述

由于Version 8 Java具有 的概念基于价值的类。这是为了准备未来的版本，很可能会定义值类型。两个定义/描述都提到序列化（我添加的粗体）：

Since Version 8 Java has the concept of value-based classes. This is in preparation of a future version which will most likely allow the definition of value types. Both definitions/descriptions mention serialization (bold face added by me):

关于现有的基于价值的类：

About the existing value-based classes:

如果程序试图将两个引用区分为基于值的类的相等值，无论是直接通过引用相等还是间接通过引发同步，身份哈希，序列化，或任何其他身份敏感机制。

A program may produce unpredictable results if it attempts to distinguish two references to equal values of a value-based class, whether directly via reference equality or indirectly via an appeal to synchronization, identity hashing, serialization, or any other identity-sensitive mechanism.

关于未来的价值类型：

通过System.identityHashCode提供的对象的默认基于身份的哈希代码也不适用于值类型。像序列化这样的基于身份的区别对象的内部操作要么不适用于值（因为它们不适用于基元），要么它们会使用值类型的hashCode提供的基于值的区别方法。

The default identity-based hash code for object, available via System.identityHashCode, also does not apply to value types. Internal operations like serialization which make identity-based distinctions of objects would either not apply to values (as they do not apply to primitives) or else they would use the value-based distinction supplied by the value type’s hashCode method.

因为未来的JVM实现可能不会使用基于值的类的对象头和引用指针，所以一些限制很明显。 （例如，没有锁定JVM必须不支持的标识。锁定的引用可以被删除并在以后被另一个替换，这使得释放锁定毫无意义并将导致死锁）。

Because future JVM implementations might not use object headers and reference pointers for value-based classes, some of the limitations are clear. (E.g. not locking on an identity which the JVM must not uphold. A reference on which is locked could be removed and replaced by another later, which makes releasing the lock pointless and will cause deadlocks).

但我不知道序列化如何发挥作用。为什么它被认为是身份敏感机制？为什么基于身份的对象区分？

But I don't get how serialization plays into this. Why is it considered an "identity-sensitive mechanism"? Why does it "make identity-based distinctions of objects"?

推荐答案

序列化使用 System.identityHashCode （通过 IdentityHashMap ）确保反序列化产生的对象图的拓扑在拓扑上等同于输入的拓扑图形。

Serialization uses System.identityHashCode (via IdentityHashMap) to ensure that the topology of the object graph resulting from deserialization is topologically equivalent to that of the input graph.

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