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An
abstract class is a class that can only be derived from;
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no
objects can be instantiated it.
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Its
purpose is to define an interface and provide a common
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base
class for derived classes.
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A
base class becomes an abstract class by making its
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constructor(s)
protected or by declaring a virtual function
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pure: virtual void statement()=0;
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Derived
classes must implement all pure virtual functions.
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If a
derived class does not implement these functions, then
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it
becomes an abstract class as well.
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Abstract
classes are not required to implement their pure
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virtual
functions.
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