What are the differences between an abstract class and an interface?

Question

Accepted Answer

Abstract class is a class that cannot be instantiated and can have both abstract and non-abstract methods. Interface is a contract that a class must adhere to.

Abstract class can have fields, constructors, and non-abstract methods, while interface cannot.
A class can inherit only one abstract class, but can implement multiple interfaces.
Abstract class can provide default implementations for some methods, while interface cannot.
Abstract class is used when there is a need for common functionality among related classes, while interface is used for providing common behavior to unrelated classes.
Example: Abstract class 'Animal' with abstract method 'makeSound', and interface 'Flyable' with method 'fly'.

Accepted Answer

Abstract class using the abstract key word
Interface using interface key word
Abstract class us collection of abstract members and non abstract memebers by default access modifier is private and abstract. 
Interface is colletion of inly abstract members by default access modifiers public
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