Inner classes and nested classes in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a nested class inside the outer class.

Kotlin

class Outer {
    class [1] {
        fun greet() = "Hello from nested class"
    }
}

Drag options to blanks, or click blank then click option'

ANested

BCompanion

CInner

DStatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using the keyword 'Inner' instead of 'Nested' for a nested class.

Trying to use 'Static' keyword which does not exist in Kotlin.

The keyword class Nested declares a nested class inside Outer. Nested classes do not hold a reference to the outer class.

2fill in blank

medium

Complete the code to declare an inner class that can access the outer class's property.

Kotlin

class Outer {
    val greeting = "Hello"
    inner class [1] {
        fun greet() = greeting
    }
}

Drag options to blanks, or click blank then click option'

AInner

BNested

CCompanion

DStatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Nested' instead of 'Inner' when access to outer class properties is needed.

Forgetting the 'inner' keyword causes no access to outer class members.

The inner keyword declares an inner class that holds a reference to the outer class instance, allowing access to its properties.

3fill in blank

hard

Fix the error in the code to correctly create an instance of the inner class.

Kotlin

class Outer {
    inner class Inner {
        fun greet() = "Hi"
    }
}

fun main() {
    val inner = Outer().[1]()
    println(inner.greet())
}

Drag options to blanks, or click blank then click option'

AOuter

Bnew

Ccreate

DInner

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to instantiate inner class without an outer class instance.

Using keywords like 'new' which are not used in Kotlin.

To create an instance of an inner class, you call it on an instance of the outer class like Outer().Inner().

4fill in blank

hard

Fill both blanks to create a nested class and call its method.

Kotlin

class Outer {
    class [1] {
        fun greet() = "Hello from nested"
    }
}

fun main() {
    val nested = Outer.[2]()
    println(nested.greet())
}

Drag options to blanks, or click blank then click option'

ANested

BInner

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Inner' keyword for nested class declaration.

Trying to instantiate nested class like an inner class.

The nested class is declared with class Nested and called with Outer.Nested().

5fill in blank

hard

Fill all three blanks to create an inner class, instantiate it, and call its method.

Kotlin

class Outer {
    val message = "Hi from outer"
    inner class [1] {
        fun greet() = message
    }
}

fun main() {
    val outer = Outer()
    val inner = outer.[2]()
    println(inner.[3]())
}

Drag options to blanks, or click blank then click option'

AInner

Cgreet

DNested

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Nested' instead of 'Inner' for the inner class.

Calling the method incorrectly or forgetting parentheses.

The inner class is declared with inner class Inner, instantiated with outer.Inner(), and its method greet() is called.