在-128到127之间的值上Int的Kotlin引用相等行为 [英] Kotlin referential equality behavior on Int with values between -128 to 127

问题描述

我要给自己直到12:00 AM，以学习和提高Kotlin的工作效率(希望).

I'm giving myself until 12:00AM to learn and get productive (hopefully) on kotlin.

遵循 https://kotlinlang.org/docs/kotlin-docs.pdf 我在第17页上尝试了这些代码片段.请问有人可以帮助我理解为什么===如果-128到127之间的值返回true吗?

Following https://kotlinlang.org/docs/kotlin-docs.pdf I tried these snippets on page 17. Could anyone please help me understand why === returns true if a value is between -128 to 127?

以下确实显示false:

val a: Int = 10000
val boxedA: Int? = a            // Integer@445
val anotherBoxedA: Int? = a     // Integer@447 why?
print(boxedA === anotherBoxedA) // false

但是将a更改为-128到127之间的任何值始终会打印true:

However changing a to any value between -128 to 127 always prints true:

val a: Int = -128
val boxedA: Int? = a            // Integer@445
val anotherBoxedA: Int? = a     // Integer@445 why?
print(boxedA === anotherBoxedA) // true!

在我看来，如果Int值在-128到127(Java字节)的范围之外，则Kotlin会在赋值时创建一个新对象，从而使引用不相等.

It seems to me if Int value is outside the bounds of -128 to 127 (Java byte) kotlin creates a new object on assignment does making the reference not equal.

推荐答案

请参见Integer.valueOf()的Java源代码，该代码负责对int值进行装箱. Javadoc说:

See the Java source code of Integer.valueOf() which is reponsible for boxing int values. The javadoc says:

此方法将始终缓存-128至127范围内的值

This method will always cache values in the range -128 to 127

因此，如果该范围内的带框整数具有相同的数值，则它们始终是同一对象.

So boxed integers in that range are always the same object if they have the same numeric value.

在Kotlin中，您应该将装箱的整数与==而不是与===进行比较.

In Kotlin, you should compare boxed Integers with == and not with ===.

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