01 - OOP (1)
Object Oriented Programming (OOP)
- Clean Code
- Defensive coding
- Iterative, Agile
- Design Patterns
- Domain Driven Design
- MS UWA, ASP.NET, etc.
Object vs Class are not the same thing. Class is the code!
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Object is the usable instance of Class.
Creating an object (from class) is often called "instantiation".
Simple analogue is that class is the blueprint and object is the house made according to blueprint.
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Fields and properties
- like variables, can be read and set directly
- Have get and set procedures, more control over values
- Auto-implementing property
- Write in VS/Rider: prop + TAB for editor help
- Need more control - have a backing field and provide logic for storing and retrieving
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Method is an action that the object can perform.
Methods can have sevaral implementations of the same method, called overloads. Number of parameters or types have to differ.
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Constructor is a class method which is exectued automatically when object is created.
- Can run only once
- Allows overloads
Default constructor is parameterless, auto created by compiler when there are no other constructors present.
VS/Rider shortcut to create a constructor: ctor+TAB
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GC (Garbage Collection) takes care of object destruction and memory management in most cases but can be used in case of unmanaged resources.
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There can only be one destructor in class
Destructors are almost never used. Usage of
IDisposable is the recommended pattern.
Events enable a class or object to notify other classes or objects when something of interest occurs.
- Events are typically used to signal user actions such as a button clicks or menu selections in graphical user interface
- Advanced topic...
A class defined within another class is called nested. By default, the nested class is private.
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Access modifiers and levels
All classes and class members can specify what access level they provide to other classes by using access modifiers.
The type or member can be accessed by any other code in the same assembly or another assembly that references it.
The type or member can only be accessed by code in the same class.
The type or member can only be accessed by code in the same class or in a derived class.
The type or member can be accessed by any code in the same assembly, but not from another assembly.
The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly.
Not all access modifiers can be used by all types or members in all contexts, and in some cases the accessability of a type member is constrained by the accessability of its containing type.
Assembly and namespace
An assembly provides a fundamental unit of physical code grouping. It is an Output Unit. It is a unit of Deployment and a unit of versioning. Assemblies contain MSIL (MS Intermediate Language) code.
A namespace provides a fundamental unit of logical code grouping. It is a collection of names wherein each name is unique. They form the logical boundary for a group of classes. Namespace must be specified in project properties.
Static classes and members
A static member of the class is a property, procedure, or field that is shared by all instances of a class.
Static classes have static members only and cannot be instantiated. Static members also cannot access non-static properties, fields or methods
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Create objects without writing a class definition for the data type.
- Compiler generates a class for you.
- The class has no usable name and contains the properties you specify in declaring the object.
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Inheritance enables you to create a new class that reuses, extends, and modifies the behavior that is defined in another class.
The class whose members are inherited is called the base class.
The class that inherits those members is called the derived class.
All classes in C# implicitly inherit from the Object class that supports .NET class hierarchy and provides low-level services to all classes.
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To specify that class cannot be used as a base class:
To specify that class can only be used as base class and cannot be instatiated:
By default, a derived class inherits all members from its base class. If you want to change the behavior of the inherited member, you need to override it.
You can define a new implementation of the method, property or event in the derived class.
The following modifiers are used to control how properties and methods are overridden:
Allows a class member to be overridden in a derived class.
Overrides a virtual (overridable) member defined in the base class.
Requires that a class member to be overridden in the derived class.
Hides a member inherited from a base class.
The virtual keyword is used to modify a method, property, indexer, or event declaration and allow for it to be overridden in a derived class.
Cannot be used with:
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The override modifier is required to extend or modify the abstract or virtual implementation of an inherited method, property, indexer, or event.
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The abstract modifier indicates that the thing being modified has a missing or incomplete implementation.
The abstract modifier can be used with classes, methods, properties, indexers, and events.
Use the abstract modifier in a class declaration to indicate that a class is intended only to be a base class of other classes.
Members marked as abstract, or included in an abstract class, must be implemented by classes that derive from the abstract class.
- Abstract class cannot be instantiated
- Sealed is not possible
- Abstract method is also virtual
- Abstract methods only in abstract class
- No implementation of methods u No static or virtual
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When used as a declaration modifier, the new keyword explicitly hides a member that is inherited from a base class.
When you hide an inherited member, the derived version of the member replaces the base class version.
Although you can hide members without using the new modifier, you get a compiler warning. If you use new to explicitly hide a member, it suppresses this warning.
Override extends, new hides.
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Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation.
They are implemented by classes, and defined as separate entities from classes.
An interface represents a contract, in that a class that implements an interface must implement every aspect of that interface exactly as it is defined.
Most of modern OOP programming is based on interfaces!
- Interfaces members are public
- You have to implement every method in interface
- Abstract class can use interfaces
- Convention – all interfaces start with capital letter I
- You can implement more than one interface
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Classes, structures, records, interfaces and methods in the .NET Framework can include type parameters that define types of objects that they can store or use.
The most common example of generics is a collection, where you can specify the type of objects to be stored in a collection.
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