Practical example regarding usage of Abstract classes and Interfaces

 Hi all ,
In which situation we go for Abstract classes and Interfaces  in OOP Programming can any body give me practical example regrding usage of Abstarc class and Interfaces because in Inheritance and Abstract class we are doing the same thing i mean declaring method as virtual and override in drieved class and in Abstract class we are decalring the method as abstract and implementing that method in Dervied class .
Guide me in above issue .
Best Regards
 
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