An in-depth analysis of SQL encapsulation, polymorphism and overload _mssql

Object-oriented

1. Class: Abstract from many objects

2. Object: Class instantiated

3. Definition of Class

Keyword class

4. The class contains

Member variable

Member properties

Member Methods

5. Object-oriented three major characteristics

(1) Package

Purpose: To protect classes and make classes more secure.

Practice: Let the member variables inside the class into private, do the appropriate method or attribute to indirectly manipulate the member variables

Encapsulates member methods to indirectly manipulate member variables within a class

Use member properties to indirectly access member variables within a class

Access modifiers

Private private can only be accessed in this class

Protected protected can only be accessed in this class and its subclasses

Public access is available anywhere

Constructor method (function):

The method to be invoked to create an object that can be initialized to a member

Each class has a construction method, not written, but not visible.

Particularity: Special execution time of writing special

This keyword:

This represents the object and does not represent the class

(2) Inheritance:

Concept: Subclasses can inherit everything from the parent class

Feature: Single inheritance A subclass can have only one parent class, and a parent class may have multiple subclasses (all parent classes are object)

Base keyword

Sealed keywords: Sealed class This class cannot be inherited

Part of class: Partial can split a class into multiple parts, and put them in multiple files

namespace namespaces are equivalent to virtual folders

(3) Polymorphism:

1. Compile polymorphism

Function overload

2. Run polymorphic

Concept: When a parent class reference points to a subclass instance, because the subclass's method of the parent class is overridden, the difference in the invocation of the method is called polymorphism

Condition: Must have inherited parent class reference point to subclass real example class must override method of parent class

The Richter substitution principle: If there is a place to use the parent object, then you can give him a subclass object

1. Function overload

Condition required for function overloading: function name to be the same, number of arguments or type of parameter different

2.this keywords

Although it is written in the class, but not in the class, it belongs to the object's

Generally within the class the This keyword can be omitted, but if there is a method parameter name and member name repetition, then call the member inside the object need to add the This keyword

3. is keyword

Determines whether a variable belongs to a type

If (y2 is Ren)
{
s = ' is a person ';
}
Else
{
s = "not a person";
}

4. As keyword

Conversion type (only compatible types can be converted, the subclass object may be converted to the parent class object)

5. Inheritance

Subclasses can inherit everything from the parent class

Features: Single inheritance

A subclass can have only one parent class, and one parent class may have multiple subclasses

C # Special points: Ancestors of all classes are object

Base keyword: Represents a parent class object in a subclass, with the same usage as the This keyword

If the parent class has a construction method, the subclass also has a construction method, and if the parent constructor requires parameters, the subclass construct must also have corresponding parameters.
The constructor method of the parent class can be invoked by base after the subclass construct

Public (string m): Base (m)
{ 
}

The above is a small set to introduce the SQL package, polymorphism and overloading, I hope to help you, if you have any questions please give me a message, small series will promptly reply to everyone. Here also thank you very much for the cloud Habitat Community website support!