CODEWITHSUNDEEP
kotlin
Lyn
Lyn

Reputation: 291

How to explain these Kotlin codes about 'Int' type?

var a: Int = 10000
var b: Int = 10000
print(b === a) // Prints 'true'

The official doc says: "a === b evaluates to true if and only if a and b point to the same object."

In the codes above, what's "the same object"?

Upvotes: 1

Views: 865

Answers (2)

Avijit Karmakar
Avijit Karmakar

Reputation: 9388

=== means we have to check the referential equality between the objects.

var a: Int = 10000
var b: Int = 10000
print(b === a)

It prints true because the reference to a and b variables are same. It's actually not an object. As the value of a and b are same that's why their reference is also same. a and b refers to the same memory allocation as their value is same. a and b are primitive type variables. So, you will get a warning

Identity equality for arguments of types Int and Int is deprecated.

var c = Integer(10000)
var d = Integer(10000)
print(d === c)

It prints false because c and d are two different Integer objects. So, the reference to c and d are also different.

Upvotes: 2

jrtapsell
jrtapsell

Reputation: 7001

How is data stored

If you imagine inside the JVM there are 2 types that are stored directly:

  • Primitive types [Int, Long]

    These are stored as the value

  • Reference types [String, Object]

    These are stored as a reference to the object

How does === work

=== compares the values in memory, so for reference types it checks they refer to the same object, whereas for primitive types it checks that they hold the same value.

Why are Ints primitive objects

Kotlin stores types that can be stored as primitives as primitives as an optimisation, so Int is primitive, whereas Int? would be stored as a reference type.

Upvotes: 1

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