Nested class independence from outer in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested class in Kotlin?

A nested class is a class defined inside another class. In Kotlin, it does not hold a reference to the outer class by default.

beginner

How does a nested class differ from an inner class in Kotlin?

A nested class is independent and cannot access members of the outer class. An inner class holds a reference to the outer class and can access its members.

beginner

Can a nested class access properties of its outer class in Kotlin?

No, a nested class cannot access properties or functions of the outer class unless it is marked as inner.

intermediate

Why might you use a nested class instead of an inner class?

Use a nested class when you want to group a class logically inside another but keep it independent, avoiding unnecessary references to the outer class.

intermediate

Show a simple Kotlin example of a nested class and explain its independence.

class Outer {
    class Nested {
        fun greet() = "Hello from Nested"
    }
}

// Usage:
val nested = Outer.Nested()
println(nested.greet())

// Explanation: Nested class does not access Outer members and can be created without an Outer instance.

In Kotlin, what does a nested class NOT have by default?

A Its own properties and methods

B Ability to be instantiated

C Reference to the outer class instance

D A name

A nested class does not hold a reference to the outer class instance unless marked as inner.

Which keyword makes a nested class able to access outer class members?

A inner

B open

C override

D companion

The 'inner' keyword allows the nested class to access members of the outer class.

How do you create an instance of a nested class in Kotlin?

A val obj = Outer().Nested()

B val obj = Outer.Nested()

C val obj = Nested()

D val obj = Outer.Inner()

A nested class instance is created using Outer.Nested() without needing an outer class instance.

Which statement is true about nested classes in Kotlin?

A They cannot have constructors.

B They can access private members of the outer class.

C They must be marked with 'static' keyword.

D They are static by default.

Nested classes in Kotlin behave like static classes in Java, meaning they do not hold an implicit reference to the outer class.

Why might you avoid using inner classes when not needed?

A They increase memory usage by holding outer class references.

B They cannot access outer class members.

C They cannot be instantiated.

D They are slower to compile.

Inner classes hold a reference to the outer class, which can increase memory usage if not necessary.

Explain the difference between a nested class and an inner class in Kotlin.

Think about how each class relates to the outer class and what members they can access.

Describe a situation where using a nested class is better than an inner class.

Consider memory and design simplicity.