Boxing of number giving true for number less than 128

Support
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val boxedA: Int? = 127
val anotherBoxedA: Int? = 127
println(boxedA === anotherBoxedA)      // Output true

val boxedB: Int? = 127
val anotherBoxedB: Int? = 127
println(boxedB === anotherBoxedB)    // Output false
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I think the compiler is free to use the same object for boxing when it feels like. And I believe a few ints, I guess up to 127 are all boxed once at startup just in case.

Is there a specific question you have about this behavior?

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Yes, as mentioned in kotlin docs, by default all elements are boxed, so they will be different reference for every object, which means whatever the value its shouldn’t be equal

4

Yes, as mentioned in kotlin docs, by default all elements are boxed

Where exactly did you read that?

https://kotlinlang.org/docs/reference/basic-types.html

On the Java platform, numbers are physically stored as JVM primitive types, unless we need a nullable number reference (e.g. Int? ) or generics are involved. In the latter cases numbers are boxed.

Java specification states that numbers from -128 to 127 are always boxed to the same object.
https://docs.oracle.com/javase/specs/jls/se8/html/jls-5.html#jls-5.1.7

All example variables are nullable so they will be boxed and if they are in range from -128 to 127, they will always point to the same object when using Kotlin on JVM.

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5

I think for range -128 to 127 by default use Int cache

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6

Boxing an Int in an object does not mean that a new object is used each time. Indeed, on the jvm all integer literals up to 128 use the same object when boxed. A practice known as interning.

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