7498ce0052
* Added a few lines to emphasize Interfaces importance to Design patterns. * Fixed several grammatical mistakes
78 lines
2.2 KiB
Markdown
78 lines
2.2 KiB
Markdown
---
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title: Interface
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---
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---
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An interface is similar to a class or struct but without implementation for its members.
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An interface declares a contract or a behavior that implementing classes should have.
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It may declare only properties, methods and events with NO access modifiers.
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All the declared members must be implemented in the inharit class, otherwise will have an compile error.
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as a convention we will mark interface with the letter I at the begenning (IMyInterface || IUserOptions).
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You define an interface by using the interface keyword.
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All members of an interface are:
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implicitly abstract,
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implicitly public, cannot declare an access modifier such as protected, internal private etc...
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An Interface can:
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* Inherit from other interfaces.
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* Inherit from multiple interfaces at the same time
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* Contain only methods, properties, events, and indexers.
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An Interface can not :
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* Inherit from a class.
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* Have implementation.
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* Have access modifiers other than public.
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* Be instantiated.
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---
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Using interfaces allows us to change our implementation in our project without breaking other parts, and only have to change the one place where the object is created.
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As interfaces do not implement any logic by themselves, they are a great tool for programmers to program against a type rather than a concrete object. This is very useful in keeping code loosely coupled. This behavior of interfaces made them imperative for implementation of Design Patterns.
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Interface Example:
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```csharp
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public Interface IUserFavoriteFood
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{
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void AddFood();
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Task<User> EatFavoriteFood(int id);
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}
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```
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---
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Interface inheritance and implementation:
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```csharp
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public class UserHungry : IUserFavoriteFood
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{
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public AddFood()
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{
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// Implementation:
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// A method to add food.
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}
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public Task<User> EatFavoriteFood(int id)
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{
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// Implementation:
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// A method to Eat food by id.
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}
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}
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```
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Every implementation can be different:
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```csharp
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public class AnotherUserHungry : IUserFavoriteFood
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{
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public AddFood()
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{
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// DIFFERENT Implementation:
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// A method to add vegan food.
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}
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public Task<User> EatFavoriteFood(int id)
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{
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// DIFFERENT Implementation:
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// A method to Eat only vegan food by id.
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}
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}
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```
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