What is abstract class. Difference between abstract class and Interface

Question

Accepted Answer

Abstract class is a class that cannot be instantiated. Interface is a collection of abstract methods.

Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
Abstract class can have instance variables, while interface cannot.
A class can implement multiple interfaces, but can only inherit from one abstract class.
Example of abstract class: Animal (cannot be instantiated). Example of interface: Runnable (collection of abstract methods).

Accepted Answer

In object-oriented programming, an abstract class is a class that is not meant to be instantiated directly, but is instead intended to be subclassed by other classes. An abstract class can have both concrete methods (i.e., methods with implementations) and abstract methods (i.e., methods without implementations).

The purpose of an abstract class is to provide a blueprint for other classes to follow. By defining a set of methods and properties in an abstract class, you can ensure that all classes that extend the abstract class have a certain set of functionality. Abstract classes can be used to define a common interface or set of behaviors for a group of related classes.

On the other hand, an interface is a collection of abstract methods and constants that can be implemented by any class. Interfaces define a contract that a class must adhere to if it implements the interface. Unlike abstract classes, interfaces cannot contain any concrete implementations of methods. They only define the method signatures and constants that must be implemented by any class that implements the interface.

The key differences between abstract classes and interfaces are:

Instantiation: An abstract class cannot be instantiated directly, while an interface cannot be instantiated at all. Instead, both abstract classes and interfaces are meant to be subclassed or implemented, respectively.
Method Implementation: An abstract class can have both concrete and abstract methods, while an interface can only have abstract methods.
Multiple Inheritance: A class can only inherit from one abstract class, but can implement multiple interfaces.
Access Modifiers: Methods and properties in an abstract class can have varying access modifiers, while methods in an interface are by default public.

In summary, abstract classes and interfaces serve different purposes in object-oriented programming. Abstract classes are meant to be extended and provide a set of common functionality to their subclasses, while interfaces define a contract that must be adhered to by any class that implements them.

What is abstract class. Difference between abstract class and Interface

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