kotlin int boxed identity

问题:

In the documentation we have

Note that boxing of numbers does not preserve identity

but the next examples give different results

val number1 = 127
val b1 : Int? = number1
val b2 : Int? = number1
print(b1 === b2) // this prints true

val number2 = 128
val c1 : Int? = number2
val c2 : Int? = number2
print(c1 === c2) // this prints false

In numbers greater than 127 works as expected but not when is above 128 (8 bits), why?

回答1:

This article explains it: http://javapapers.com/java/java-integer-cache/

The basic idea is that the Java standard lib uses a cache for values between -128 and 127, therefore they always refer to the same Integer object (by identity).