Interface vs. Class: When Should You Choose Which?

Interfaces vs. Classes: When to Choose Which? ——Comprehensive Guide

In software engineering, it is crucial to understand the difference between interfaces and classes. While both are important language constructs, their purposes and applications are quite different.

What is an interface?

An interface defines a contract that specifies the methods that a class must implement. It acts as a blueprint for a class, outlining the methods that must be available without providing their concrete implementations. A class that implements an interface must provide definitions for all of its declared methods.

The difference between interfaces and classes

• Declaration: Interfaces are declared using the interface keyword, while classes are declared using the class keyword.
• Implementation: Interfaces do not provide method implementations, while classes contain method declarations and their implementations.
• Inheritance: Interfaces can only be implemented by classes, and classes can inherit from other classes or implement interfaces.
• Multiple implementations: A class can implement multiple interfaces to support multiple functions.

Why use interfaces?

Although it is possible to implement methods directly in classes, there are compelling reasons to use interfaces:

• Contract Encapsulation: An interface defines the characteristics required by a class, making it easier to ensure that an implementation conforms to a specified contract.
• Loose Coupling: By decoupling the interface from the implementation, it reduces the coupling between components. A class can change its internal implementation without affecting code that depends on the interface.
• Extensibility: Interfaces promote extensibility by allowing new classes that satisfy the same contract to be added without modifying existing code.
• Polymorphism: Interfaces enable polymorphism by allowing objects of different types that implement the same interface to be processed in a uniform manner.

Example:

Consider the following code snippet:

<code>interface ILogInterface
{
    void WriteLog();
}

class MyClass : ILogInterface
{
    public void WriteLog()
    {
        Console.Write("MyClass was Logged");
    }
}

class MyLogClass
{
    public void WriteLog(ILogInterface myLogObject)
    {
        myLogObject.WriteLog();
    }
}</code>

Here, ILogInterface defines the logging contract, and MyClass implements it. MyLogClass now accepts any object that implements ILogInterface, allowing different classes to implement their own logging behavior. This demonstrates the loose coupling and extensible nature of the interface.

In summary, interfaces are powerful tools for defining contracts, achieving loose coupling, promoting extensibility, and promoting polymorphism. While classes provide direct implementation, interfaces serve as abstractions that define expected behavior, making them invaluable in a variety of software design scenarios.

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