Abstract methods in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an abstract method in TypeScript?

An abstract method is a method declared in an abstract class without an implementation. Subclasses must provide their own implementation of this method.

beginner

Can you create an instance of an abstract class that contains abstract methods?

No, you cannot create an instance of an abstract class. Abstract classes are meant to be extended by other classes that implement the abstract methods.

beginner

How do you declare an abstract method in TypeScript?

Use the keyword abstract before the method name and do not provide a method body. For example: abstract greet(): void;

intermediate

Why use abstract methods in a class?

Abstract methods enforce that subclasses implement specific methods, ensuring a consistent interface while allowing different behaviors in each subclass.

intermediate

What happens if a subclass does not implement all abstract methods from its abstract superclass?

The TypeScript compiler will give an error because the subclass must implement all abstract methods or be declared abstract itself.

Which keyword is used to declare an abstract method in TypeScript?

A override

B abstract

C virtual

D interface

The keyword abstract is used to declare abstract methods in TypeScript.

Can you instantiate an abstract class directly?

A No, never

B Only if it has a constructor

C Only if it has no abstract methods

D Yes, always

Abstract classes cannot be instantiated directly in TypeScript.

What must a subclass do if it extends an abstract class with abstract methods?

A Remove the abstract keyword

B Ignore abstract methods

C Declare itself abstract

D Implement all abstract methods

Subclasses must implement all abstract methods or be declared abstract themselves.

Which of the following is true about abstract methods?

A They have no implementation in the abstract class

B They can be called directly on the abstract class

C They are optional to implement in subclasses

D They are private methods

Abstract methods have no implementation in the abstract class and must be implemented in subclasses.

What error occurs if a subclass does not implement an abstract method?

A Syntax error

B Runtime error

C Compiler error

D No error

TypeScript compiler throws an error if a subclass does not implement all abstract methods.

Explain what an abstract method is and why it is useful in TypeScript classes.

Think about how abstract methods guide subclasses.

Describe the rules for subclassing an abstract class with abstract methods in TypeScript.

Focus on what the subclass must do with abstract methods.