CODEWITHSUNDEEP
classkotlinoopinterface
EduSantino
EduSantino

Reputation: 1

How to get a value from a field inside an nested class?

I'm trying to get a value of a field from inside a nested class in Kotlin, however, I'm having some difficulties with the logic. Somewhere I saw that it is possible through an interface, but I don't know where to start.

A simple sample:

class ExternalClass {
       
     class InternalClass {
           val internalValue = 2
     }

     val externalValue = InternalClass().internalValue
}


fun main(args: Array<String>) {

    print(ExternalClass().externalValue)
}

The easiest way (and most obvious) to achieve this would be to instantiate the InternalClass class inside the External, however, in some cases, it would be necessary to pass several parameters in the Internal's constructor, which would not be the case.

So how would it be possible to do this through an interface?

Any idea or insight will be welcome!

Thank you!

Upvotes: 0

Views: 461

Answers (1)

Tenfour04
Tenfour04

Reputation: 93649

Taking a step back, it is nonsensical for the outer class to want to access a stateful property of some arbitrary instance of the nested class. There's no reason for an arbitrary instance's state to be useful. The only reason the outer class would need to access a property of the other class is if it is doing something with a specific instance of the inner class, in which case it would already have an instance of it on which to access its property.

In your example code, the nested class is weird because it defines a property that can only ever hold a value of 2. So every instance of the class is reserving memory for a property to hold a duplicate of that same value, even though it should really be a constant that is shared by all instances.

If the value you want to access is a constant (the same value for all instances), then it would make sense to want to access it regardless of instance because it doesn't have anything to do with a specific instance. To make it constant, it should be defined in a companion object like this. Then it can be accessed through the name of the nested class without creating an instance of it.

class ExternalClass {
       
     class InternalClass {
           companion object {
               val internalValue = 2
           }
     }

     val externalValue = InternalClass.internalValue
}

An interface would have nothing to do with this kind of thing.

Upvotes: 1

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