What is an abstract class?

Imagine you have some set of inter related classes like mango , apple ,banana all these classes are having same functionality so instead of creating again repeated methods in these classes i will create a more generalized method fruits and in that i define the idea means how to do it and later on sub classes will implement those ideas so in a company many people will work for 2 or 3 years and leave the company we cant take the code of them what they have written i mean to say in projects many people mainly project managers create abstract classes and later on sub ordinates will use or override the function of that idea which is present in abstract class like that it works.when project are very big we just modify the code in abstract class it will automatically modified in sub class it is like kind of relationship eg : mango is kind of fruit like that read less