Inner class access to outer members in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of inner class accessing outer class property

What is the output of this Kotlin code?

Kotlin

class Outer {
    val greeting = "Hello"
    inner class Inner {
        fun greet() = "$greeting from Inner"
    }
}

fun main() {
    val inner = Outer().Inner()
    println(inner.greet())
}

A Hello

B Error: Cannot access 'greeting' from Inner

C from Inner

D Hello from Inner

💡 Hint

Remember that inner classes have access to outer class members.

In Kotlin, an inner class can access members of its outer class instance. Here, 'greeting' is accessed directly inside the inner class method.

❓ Predict Output

intermediate

Output when inner class shadows outer property

What will be printed by this Kotlin program?

Kotlin

class Outer {
    val value = 10
    inner class Inner {
        val value = 20
        fun printValues() {
            println(value)
            println([e-mail])
        }
    }
}

fun main() {
    Outer().Inner().printValues()
}

A

10
20

B

20
10

C

20
20

D

10
10

💡 Hint

Use 'this@Outer' to refer to the outer class instance.

The inner class has its own 'value' property which shadows the outer class's 'value'. 'value' alone refers to inner's property, '[e-mail]' refers to outer's property.

🔧 Debug

advanced

Why does this code cause a compilation error?

This Kotlin code tries to access an outer class property from a nested class but fails. Why? class Outer { val name = "Outer" class Nested { fun printName() { println(name) } } } fun main() { Outer.Nested().printName() }

A Nested class is not inner, so it cannot access outer class members directly.

B The property 'name' is private and inaccessible.

C The syntax for accessing outer class members is incorrect.

D Nested classes cannot have functions in Kotlin.

💡 Hint

Check the difference between 'inner' and 'nested' classes in Kotlin.

In Kotlin, nested classes are static by default and do not hold a reference to the outer class instance. Only inner classes can access outer class members directly.

❓ Predict Output

advanced

Output of inner class accessing outer class function

What is the output of this Kotlin program?

Kotlin

class Outer {
    fun outerFun() = "Outer Function"
    inner class Inner {
        fun callOuter() = outerFun()
    }
}

fun main() {
    println(Outer().Inner().callOuter())
}

A Outer Function

B Error: Cannot call outerFun from Inner

C null

D Outer

💡 Hint

Inner classes can call outer class functions directly.

The inner class method 'callOuter' calls the outer class function 'outerFun' directly, so it returns 'Outer Function'.

🧠 Conceptual

expert

How to access outer class property when inner class has same property name?

In Kotlin, if an inner class has a property with the same name as the outer class, how can you access the outer class property inside the inner class?

A Use 'Outer.propertyName' directly without any qualifier.

B Use 'super.propertyName' inside the inner class.

C Use '[e-mail]' to refer to the outer class property.

D It's not possible to access outer class property if names clash.

💡 Hint

Kotlin provides a special syntax to refer to outer class instance.

The syntax 'this@Outer' refers to the instance of the outer class, allowing access to its members even if shadowed.