What is exact difference between Inheritance and Abstract class?

Question

I know the fundamentals of OOP concepts[Inheritance, Abstraction, Encapsulation, Polymorphism]

We use Inheritance in case of Parent-Child relationship[C

Answer 1

Inheritance is for inheriting properties and having some of its own as well.

Abstract is to restrict from being instantiated.

Example:
Lets take Vehicle and VehiclePart. But Vehicle as such is very abstract and not complete. So we want Vehicle class abstract because we don't want to instantiate it directly. Car is more meaningful entity than Vehicle and car is a Vehicle. So car extends vehicle and it is not abstract.

abstract class Vehicle{
    String name;
}

abstract class VehiclePart{
    String name;
    Date expiry;
}

class Car extends Vehicle{
     List parts;
}

class RacingCar extends Vehicle{

}

class Gear extends VehiclePart{
   int numOfGears;
}

Inheritance: We need to override the method in child class

Nope. in the above example you can see Car is inheriting properties like name from Vehicle. Overriding is optional. Like RacingCar can override methods of Car and make it a little bit custom. But basically it is getting(inheriting) some properties from base class. Like all the basic properties of a car will in Car and not in RacingCar. RacingCar will have properties specific to it.

Abstract class: Put abstract keyword in method name and need to implement the method in child class

Nope. It is just to restrict its instantiation. Eg. We don't want to instantiate Vehicle object because there is no meaning to it. A vehicle has to be something like car, bus etc etc. It can't just be a vehicle. So we put abstract and restrict instantiation.