Open classes and methods in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the open keyword mean in Kotlin?

In Kotlin, <code>open</code> means a class or method can be inherited or overridden. By default, classes and methods are <code>final</code> and cannot be changed.

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Why are classes and methods final by default in Kotlin?

Kotlin makes classes and methods final by default to avoid accidental inheritance or overriding, which helps keep code safer and easier to understand.

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How do you make a class inheritable in Kotlin?

Add the <code>open</code> keyword before the class name. For example: <code>open class Animal</code> allows other classes to inherit from <code>Animal</code>.

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How do you allow a method to be overridden in Kotlin?

Mark the method with open. For example: open fun speak() {} lets subclasses provide their own version of speak().

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What happens if you try to override a method that is not marked open?

Kotlin will give a compile error because only open methods can be overridden. This prevents accidental changes to important behavior.

In Kotlin, what keyword do you use to allow a class to be inherited?

A open

B final

C override

D abstract

The open keyword allows a class to be inherited. Classes are final by default.

What is the default behavior of classes in Kotlin regarding inheritance?

A They are abstract

B They are open for inheritance

C They are final and cannot be inherited

D They are interfaces

By default, Kotlin classes are final and cannot be inherited unless marked open.

Which keyword allows a method to be overridden in Kotlin?

A abstract

B override

C final

D open

The open keyword marks a method as overridable. override is used when overriding.

What happens if you try to override a method not marked as open?

A It works normally

B You get a compile-time error

C The method becomes abstract

D The method is ignored

Kotlin prevents overriding methods that are not open by giving a compile-time error.

Which of these is true about open classes and methods?

A They can be inherited or overridden

B They cannot be inherited or overridden

C They are abstract by default

D They are deprecated

open means classes or methods can be inherited or overridden.

Explain what the open keyword does in Kotlin and why it is important.

Think about how Kotlin protects your code by default and how <code>open</code> changes that.

Describe the difference between a class marked open and one that is not in Kotlin.

Focus on inheritance and overriding permissions.