Introduction
An Abstract class is a class that provides a common definition to the subclasses and this is the type of class whose object is not created.
Key points of Abstract Classes
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Abstract classes are declared using the abstract keyword.
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We cannot create an object of an abstract class.
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If you want to use it then it must be inherited in a subclass.
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An Abstract class contains both abstract and non-abstract methods.
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The methods inside the abstract class can either have an implementation or no implementation.
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We can inherit two abstract classes; in this case the base class method implementation is optional.
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Methods inside the abstract class cannot be private.
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Abstract classes are useful when you need a class for the purpose of inheritance and polymorphism.
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The purpose of an abstract class is to provide default functionality to its subclasses.
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When a class contains at least one abstract method, then the class must be declared as an abstract class.
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It is mandatory to override the abstract method in the derived class.