what is difference between abstract class and interface with real time

An interface has only abstract methods (method without body) but an abstract class can have both abstract as well as non abstract methods (methods with body), so it can also support access modifiers (private,internal etc) but interface has by default public methods only.

so, it is a common practice that whenever you have to create contract (force child class to implement and use same naming conventations) we use interface.

Another benefit of interface is to achieve loose coupling between two projects or classes. we use interface instead of concrete objects which also hides the real implementions from caller class.

public class EmployeeBL
{
private IDepartmentBL _DepartmentBL;
public Employee(IDepartmentBL DepartmentBL)
{
_DepartmentBL=DepartmentBL;
}
public Department DepartmentByEmployeeId(int id)
{
return _DepartmentBL.DepartmentByEmployeeId(id);
}
}

so, caller doesn't know which implementation out of the given two implementions, _DepartmentBL pointing to, and will be resolved at run time using dependency injection.

public Interface IDepartmentBL
{
Department DepartmentByEmployeeId(int id);
}
public class DepartmentBL1 :IDepartmentBL
{
public Department DepartmentByEmployeeId(int id)
{
return Departmets.Where(x=>x.EmployeeId==id).singleOrDefault();
}
}
}
public class DepartmentBL2 :IDepartmentBL
{
public Department DepartmentByEmployeeId(int id)
{
return Departmets.Where(x=>x.EmployeeId==id).singleOrDefault();
}
}
}

2 Replies

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Sachin Singh4y ago
Accepted answer
An interface has only abstract methods (method without body) but an abstract class can have both abstract as well as non abstract methods (methods with body), so it can also support access modifiers (private,internal etc) but interface has by default public methods only.
so, it is a common practice that whenever you have to create contract (force child class to implement and use same naming conventations) we use interface.
Another benefit of interface is to achieve loose coupling between two projects or classes. we use interface instead of concrete objects which also hides the real implementions from caller class.
public class EmployeeBL
{
private IDepartmentBL _DepartmentBL;
public Employee(IDepartmentBL DepartmentBL)
{
_DepartmentBL=DepartmentBL;
}
public Department DepartmentByEmployeeId(int id)
{
return _DepartmentBL.DepartmentByEmployeeId(id);
}
}
so, caller doesn't know which implementation out of the given two implementions, _DepartmentBL pointing to, and will be resolved at run time using dependency injection.
public Interface IDepartmentBL
{
Department DepartmentByEmployeeId(int id);
}

public class DepartmentBL1 :IDepartmentBL
{
public Department DepartmentByEmployeeId(int id)
{
return Departmets.Where(x=>x.EmployeeId==id).singleOrDefault();
}
}
}

public class DepartmentBL2 :IDepartmentBL
{
public Department DepartmentByEmployeeId(int id)
{
return Departmets.Where(x=>x.EmployeeId==id).singleOrDefault();
}
}
}
Muhammad Imran Ansari4y ago
Please follow the step by step article with code examples:
https://www.c-sharpcorner.com/article/when-to-use-abstract-class-and-interface-in-real-time-projects/