Difference between Abstract Classes and Interfaces
| Abstract | Interface |
|---|---|
| Abstract class can have abstract and non-abstract methods . | Interface can have only abstract methods and abstract class can have field/property but interface not allow it. |
| Abstract class doesn’t support multiple inheritance | Interface supports multiple inheritance. |
| It can use access modifier | But interface wont have it because within an interface by default everything is public |
| It can have final, static ,non-final and non-static variables | Interface has only final variables and static |
| It can provide the implementation of interface | Interface can’t provide the implementation of abstract class |
Let us discuss the difference one by one with simple example.
Abstract class can have abstract and non-abstract methods. Interface can have only abstract methods and abstract class can have field/property but interface not allow it.
Abstract Class:
public abstract class Employee
{
public string FirstName;
public string LastName;
public override int GetFullName()
{
return this.FirstName + " " + this.LastName;
}
}
Interface : Wrong
public interface IEmployee
{
// Cant use field in interface
public string FirstName;
public string LastName;
//Implementation & access specifier will not accept
public int GetFullName()
{
return this.FirstName + " " + this.LastName;
}
}
Interface : With Proper
public interface IEmployee
{
void GetFullName();
}
Note : In simple, An abstract class can has implementation or non-implemented methods but interface can’t have implementation for any of its method.
Abstract class doesn’t support multiple inheritance. Interface supports multiple inheritance.
It’s not possible to inherite more than one abstract class. For example, if we having two abstract class namely Employee , EmployeePersonalDetails.
Abstract: Error
//Multiple class can't be inherit.
class PartTimeEmployee : Employee ,EmployeePersonalDetails
{
... code here....
}
Interface: It support multiple inheritance
class PartTimeEmployee : IEmployee ,IEmployeePersonalDetails
{
... code here....
}
An abstract class can access modifier but interface wont have it because within an interface everything is public in default.
Interface : Incorrect
public interface IEmployee
{
public void GetFullName();
}
Interface : Correct
public interface IEmployee
{
void GetFullName();
}