java - 共享调用和引用调用是否仅在多线程时有所不同？

Question

如果使用Call-by-Reference 调用函数，则对函数内变量所做的任何更改都会立即影响调用者。对于 Call-by-Sharing，它在函数结束时受到影响。

问题 1:Java 是否使用Call-by-Sharing 而不是 Call-by-Reference？

问题 2:我认为 Call-by-Sharing 不同于 Call-by-Reference only而多线程。创建它只是为了减少在其他线程中使用时并发覆盖值；提供一致性。我说得对吗？

Answer 1

我建议您不要使用“共享调用”术语。作为this Wikipedia article状态:

"However, the term "call by sharing" is not in common use; the terminology is inconsistent across different sources. For example, in the Java community, they say that Java is pass-by-value, whereas in the Ruby community, they say that Ruby is pass-by-reference[citation needed], even though the two languages exhibit the same semantics. Call-by-sharing implies that values in the language are based on objects rather than primitive types."

和

"Although this term has widespread usage in the Python community, identical semantics in other languages such as Java and Visual Basic are often described as call-by-value, where the value is implied to be a reference to the object."

底线是 Java 使用“通过共享调用”......但他们不这么调用它，如果你想让 Java 人理解你，你可能也不应该这样称呼。

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I think that Call-by-Sharing differs from Call-by-Reference only while multithreading. It is created only to decrease concurrent over-writing of values while it is being used in some other thread; to provide consistency. Am I right?

不，你不对。

在值是对象引用的情况下，“共享调用”的真正含义是“按值调用”。真正的“通过引用调用”意味着您(实际上)正在传递一个变量的地址，并且被调用的方法可以更新该变量。