What are the differences between Abstract Class and Interface in C# 8.0 and later?
C# 8.0 introduced significant enhancements to interfaces, making them more powerful and flexible. However, I am a bit confused about the specific changes, their purpose and how they improve development. Could someone explain the key differences between abstract classes and interfaces in C# 8.0 and later?
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Below is the major differences between Abstract Class and Interface in C# 8.0 and later?
- Method Implementations
- Abstract Class : Can have both abstract and concrete methods
- Interface : Can have abstract, default and static methods
- Constructors
- Abstract Class : ✅ Can have constructors
- Interface : ❌ Cannot have constructors
- Fields
- Abstract Class : ✅ Can have instance and static fields
- Interface : ✅ Can have static fields but ❌ no instance fields
- Multiple Inheritance
- Abstract Class : ❌ A class can inherit only one abstract class
- Interface : ✅ A class can implement multiple interfaces
- Access Modifiers
- Abstract Class : ✅ Supports public, protected, private and internal members
- Interface : ✅ Supports public and private members but ❌ no protected
- State Management
- Abstract Class : ✅ Can have instance fields to store state
- Interface : ❌ Cannot store instance state
- Use Case
- Abstract Class : Used when an object shares common behavior and state
- Interface : Used when only behavior needs to be enforced
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In C# 8.0 and later, interfaces became much more powerful.
They can now include default implementations, static methods and private helper methods, which were previously possible only in abstract classes.
However, the main difference still remains:
- Abstract classes can have fields, constructors and state and are used when you want to share both behavior and data among related classes.
- Interfaces define capabilities, they can now share behavior (via default methods) but cannot hold state.
So, after C# 8.0:
Use abstract classes when you need shared data or base logic,
and interfaces when you need flexible, reusable contracts (possibly with default behavior).
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In C# 8.0 and later, interfaces evolved they can now include default method implementations, static members and private methods. This lets developers add new methods to interfaces without breaking existing implementations.
The key difference is:
- Abstract classes can maintain state (fields, constructors) and share both data and logic.
- Interfaces still define contracts, but now can include optional logic for flexibility and backward compatibility.
Simply put:
Abstract classes = share structure and state.
Interfaces = share behavior and contracts.