"Byte" 个数字的 Kotlin 引用相等性

Question

在 Kotlin 官方参考资料中 https://kotlinlang.org/docs/reference/basic-types.html#numbers 我读到：

Note that boxing of numbers does not necessarily preserve identity

以及说明如何表示的示例：

val a: Int = 10000
print(a === a) // Prints 'true'
val boxedA: Int? = a
val anotherBoxedA: Int? = a
print(boxedA === anotherBoxedA) // !!!Prints 'false'!!!

经过一些自发测试后，我意识到它对于字节数 (<128) 应该可以正常工作：

val a = 127
val boxedA: Int? = a
val anotherBoxedA: Int? = a
print(boxedA === anotherBoxedA) //!!!Prints 'true'!!!

也在同一参考资料中 https://kotlinlang.org/docs/reference/equality.html 我发现：

For values which are represented as primitive types at runtime (for example, Int), the === equality check is equivalent to the == check

但这并不能解释这种情况：

val a = 128
val boxedA: Int? = a
val anotherBoxedA: Int? = a
print(boxedA === anotherBoxedA) //!!!Prints 'false'!!!

所以我想弄清楚为什么引用相等性“===”对数字 >=128 显示 "false" 而对 <128 显示 "true"？

Answer 1

这来自 Integer.valueOf(int) 是如何为 JVM 实现的：

This method will always cache values in the range -128 to 127, inclusive, and may cache other values outside of this range.

因此，对于 a = 127，恒等式 box1 === box2 始终成立，而对于所有非 byte 值，它可能不成立。

"Byte" 个数字的 Kotlin 引用相等性

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