Object oriented programming in .net o.starosotskaya.pdf · Abstract classes vs interfaces Feature...

OOP

Object oriented programming

OOP

Inheritance

Polymorphism

Encapsulation

Class concepts

• Classes can contain:

• Constants

• Delegates

• Events

• Fields

• Constructors

• Destructors

• Properties

• Methods

• Nested classes

Encapsulation

• Public The type or member can be accessed by any other code in the same assembly or another assembly that references it.

• Private The type or member can be accessed only by code in the same class or struct.

• Protected The type or member can be accessed only by code in the same class or struct, or in a class that is derived from that class.

• Internal The type or member can be accessed by any code in the same assembly, but not from another assembly.

Access modifiers

Access modifiers. Combined.

Access modifiers. Protected internal.

Access modifiers. Protected internal.

Access modifiers. Protected internal.

Access modifiers. Auto-property.

Access modifiers. Best practice

• Reasons to prefer public property over public field

• Serialization

• Reflection

• Testing

• Debugging

• Logging

• Used for data binding

Useful keywords

Readonly

declaration or in a constructor

Value is set when instance is created

Const

initialized at the declaration

Value is set once before compiling

Inheritance & Polymorphism

• No multiple inheritance in C#

• Classes can be inherited

• Interfaces can be implemented

Interfaces

• “Can – do” logics

• Interfaces can contain:

– Properties

– Events

– Methods

– Indexers

• Always public

• Cannot be initiated directly

• Classes can implement one or more interfaces

Abstract classes

• “Is a” – logics

• Can contain whatever a usual class can

• Cannot be initialized directly

• Class can inherit only one

• abstract class

Abstract classes vs interfaces

Feature Interface Abstract class

Multiple inheritance A class may inherit several interfaces.

A class may inherit only one abstract class.

Default implementation An interface cannot provide any code, just the signature.

An abstract class can provide complete, default code and/or just the details that have to be overridden.

Access Modfiers An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public

An abstract class can contain access modifiers for the subs, functions, properties

Abstract classes vs interfaces

Feature Interface Abstract class

Core VS Peripheral Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface

An abstract class defines the core identity of a class and there it is used for objects of the same type.

Homogeneity If various implementations only share method signatures then it is better to use Interfaces.

If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.

Speed Requires more time to find the actual method in the corresponding classes

Fast

Abstract classes vs interfaces

Feature Interface Abstract class

Adding functionality (Versioning)

If we add a new method to an Interface then we have to track down all the implementations of the interface and define implementation for the new method.

If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.

Fields and Constants No fields can be defined in interfaces

An abstract class can have fields and constrants defined

Overriding

Overriding

Inheritance

Composition

Composition over inheritance

• Prefer composition over inheritance

• do not use a compose-always approach

• it's easy to change behavior on the fly with Dependency Injection / Setters with composition

• Inheritance is more rigid

Composition over inheritance

• Inheritance acid rule:

Does TypeB want to expose the complete interface (all public methods no less) of TypeA such that TypeB can be used where TypeA is expected?

• Prefer composition

Does TypeB only want only some/part of the behavior exposed by TypeA?

Multiple interfaces implementation

Implicit implementation

Explicit implementation

Explicit vs implicit implementation

• Implicit always public

• Explicit always private

• No virtual for explicit

• No abstract for explicit

Design patterns

• In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.

Singleton

Lazy initialization

Abstract factory

Other interesting patterns

These patterns you will definitely need:

- Strategy

- Decorator

- Prototype

- Builder

- Facade

- Dependency injection

- Mediator

Generics

Powerful tool since c# 2.0

Point classes:

• Should contain values with floating points

• Should contain integer values

• Should log values every time the coordinates are changed

Generics

Generics

Generics with where

business, evolved.