What is an Abstract Class? When is it used?
Abstract Class
An abstract class is a class intended to serve as a base abstraction and cannot normally be instantiated directly. It can contain both implemented methods and abstract methods that derived classes must implement. I use an abstract class when related types share common state, invariants, or implementation, while still requiring subclasses to provide specific behavior. It is particularly useful when there is a genuine IS-A relationship and some common behavior belongs in the base class.
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Cannot normally be instantiated directly.
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Can contain abstract and concrete methods.
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Can contain instance state and constructors.
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Useful for sharing common implementation among closely related types.
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Should represent a meaningful abstraction rather than being used merely for code reuse.
Follow-up Questions
- Can an abstract class have a constructor?
- Can an abstract class contain concrete methods?
- Can an abstract class implement an interface?
- What is the difference between an abstract class and an interface?