Inner class access to outer members in Kotlin - Step-by-Step Execution

Concept Flow - Inner class access to outer members

Create Outer Class Instance

↓

Create Inner Class Instance

↓

Inner accesses Outer member

↓

Print or use Outer member value

↓

End

The inner class is created inside the outer class and can access the outer class's members directly.

Execution Sample

Kotlin

class Outer {
    val outerVal = "Hello from Outer"
    inner class Inner {
        fun printOuter() = println(outerVal)
    }
}
fun main() {
    val inner = Outer().Inner()
    inner.printOuter()
}

This code creates an outer class with an inner class that accesses and prints a member of the outer class.

Execution Table

Step	Action	Evaluation	Result
1	Create Outer instance	Outer instance created	outerVal = "Hello from Outer"
2	Create Inner instance from Outer	Inner instance created	Can access outerVal
3	Call Inner.printOuter()	Access outerVal from Outer	Prints: Hello from Outer
4	End of main	Program ends	Output complete

💡 Program ends after printing outerVal accessed by inner class

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
outerVal	N/A	"Hello from Outer"	"Hello from Outer"	"Hello from Outer"	"Hello from Outer"
Outer instance	N/A	Created	Created	Created	Created
Inner instance	N/A	N/A	Created	Created	Created

Key Moments - 2 Insights

How does the inner class access the outer class's member without creating a new instance?

The inner class holds a reference to its outer class instance, so it can directly access outerVal as shown in step 3 of the execution_table.

Why do we need to create the inner class instance from an outer class instance?

Because the inner class is tied to an outer instance, you must create it via Outer().Inner() as shown in step 2, ensuring it can access outer members.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of outerVal after step 1?

A Undefined

B null

C "Hello from Outer"

D "Hello from Inner"

💡 Hint

Check the 'Result' column in row for step 1 in execution_table.

At which step is the inner class instance created?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table to find when Inner instance is created.

If we tried to create Inner instance without Outer instance, what would happen?

A It would work fine

B Compilation error because Inner needs Outer instance

C Runtime error only

D Inner class would create its own Outer instance automatically

💡 Hint

Recall key_moments about how Inner class is tied to Outer instance.

Concept Snapshot

Inner classes in Kotlin can access outer class members directly.
Create inner instance via Outer().Inner() to link them.
Inner class holds reference to outer instance.
Use inner class methods to access outer members.
This allows clean encapsulation and access.

Full Transcript

This example shows how an inner class in Kotlin can access members of its outer class. First, an Outer class instance is created with a member outerVal. Then, an Inner class instance is created from the Outer instance. The inner class method printOuter accesses outerVal directly and prints its value. The execution table traces these steps, showing variable states and actions. Key points include that the inner class holds a reference to the outer instance, so it can access outerVal without creating a new Outer. The inner instance must be created from an existing Outer instance. The visual quiz tests understanding of these steps and relationships.