Lesson 45 - Static vs Instance Members

Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps

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In this lesson, we're going to cover static vs instance class members. Simply put, a static method or property is one which belongs to – and is therefore accessible via – the class itself, without having to create an instance in order to access it. You may have noticed, in previous lessons, that there were some methods that were called without going through an instance in order to call it; there was no “new” keyword involved before we could access these methods:


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Step 1: Using Intellisense to Identify Static Methods and Properties

All of these methods are static. The easiest way to distinguish static from instance methods is that they are accessible through the class name that they belong to. If you start typing a class name into Visual Studio, Intellisense will show you what static methods and properties are available to the type itself:


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To demonstrate this difference between static and instance methods, fields and properties, create a simple class that contains both:


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And now in another class, let’s create an instance to see what’s available to it via Intellisense. Note how the static field and static method are not available through the instance:


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Also, note how the instance field and method are not available through referencing the class itself:


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Tip:

As a beginner, it’s recommend that you not use the static keyword in your own classes unless they're classes that only contain public helper methods and that they don't contain any properties.

Step 2: Using Static Keyword for Helper Methods

A common use for the static keyword is for whenever there is a public helper method that performs some function that isn’t instance specific. Perhaps the method just processes some data and outputs it to the screen, for example. Here is a very contrived example:


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Notice how the static method PerformCalculation() references the other static method handleSomePartOfTheCalculation(). This is perfectly fine, however, it would not be possible for the static method to reference an instance method even if they both belong to the same class:


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The reason this is not allowed is because instance methods, in principle, have access to (1) instance fields, properties, and methods with its own class. If handleSomePartOfTheCalculation() were to (2) reference an instance property, then PerfomCalculation() would (3) also be referencing that instance property (although indirectly). However, since PerformCalculation() is statically accessible, handleSomePartOfTheCalculation() wouldn’t know what instance, if any, is being referenced:


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The reason why this doesn’t work becomes obvious when we try to call the static method:


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Step 3: An Instance Can Reference a Static, But not Vice Versa

We have no way of knowing what instance is being referenced by this static method, and neither does the compiler. That is why a static method can only access other static methods and properties. However, the inverse is possible, which is to say that an instance method can access a static property. Here, we’re creating a simple static property that can count each time a new instance of type Valuation is created:


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Step 4: Making an Entire Class Static

You can also mark an entire class as static, and the only time you would do that is if the class only holds static helper methods. Note that if you do mark a class as static, it is no longer able to hold any non-static fields, properties, or methods:


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Step 5: Snapshot of the Static Math Class

One such class that exists in the .NET Framework is the Math class, which is a static class that only holds static methods (for performing common calculations), along with a few constants:


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As you can see, the helper methods in the Math class are all static because all they do is return some sort of numerical value. An instance is not needed to do a basic calculation:


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You can find more information about this class and its methods by visiting:

http://v.gd/static


Related Articles in this Tutorial:

Lesson 1 - Series Introduction

Lesson 2 - Installing Visual Studio 2015

Lesson 3 - Building Your First Web App

Lesson 4 - Understanding What You Just Did

Lesson 5 - Working with Projects in Visual Studio

Lesson 6 - Simple Web Page Formatting in Visual Studio

Challenge 1

Solution 1

Lesson 7 - Variables and Data Types

Lesson 8 - Data Type Conversion

Lesson 9 - Arithmetic Operators

Lesson 10 - C# Syntax Basics

Challenge 2 - ChallengeSimpleCalculator

Solution - ChallengeSimpleCalculator

Lesson 11 - Conditional If Statements

Lesson 12 - The Conditional Ternary Operator

Challenge 3 - ChallengeConditionalRadioButton

Solution - Challenge Conditional RadioButton

Lesson 13 - Comparison and Logical Operators

Lesson 13 Challenge - First Papa Bob's Website

Solution - Challenge First Papa Bob's Website

Lesson 14 - Working with Dates and Times

Lesson 15 - Working With Spans of Time

Lesson 16 - Working with the Calendar Server Control

Challenge 4 - Challenge Days Between Dates

Solution - Challenge Days Between Dates

Lesson 17 - Page_Load and Page.IsPostBack

Lesson 18 - Setting a Break Point and Debugging

Lesson 19 - Formatting Strings

Challenge 5 - Challenge Epic Spies Assignment

Solution - Challenge Epic Spies Assignment

Lesson 20 - Maintaining State with ViewState

Lesson 21 - Storing Values in Arrays

Lesson 22 - Understanding Multidimensional Arrays

Lesson 23 - Changing the Length of an Array

Challenge 6 - Challenge Epic Spies Asset Tracker

Solution - Challenge Epic Spies Asset Tracker

Lesson 24 - Understanding Variable Scope

Lesson 25 - Code Blocks and Nested If Statements

Lesson 26 - Looping with the For Iteration Statement

Challenge 7 - Challenge For Xmen Battle Count

Solution - Challenge For Xmen Battle Count

Lesson 27 - Looping with the while() & do...while() Iteration Statements

Lesson 28 - Creating and Calling Simple Helper Methods

Lesson 29 - Creating Methods with Input Parameters

Lesson 30 - Returning Values from Methods

Lesson 31 - Creating Overloaded Methods

Lesson 32 - Creating Optional Parameters

Lesson 33 - Creating Names Parameters

Lesson 34 - Creating Methods with Output Parameters

Challenge 8 - Challenge Postal Calculator Helper Methods

Solution - Challenge Postal Calculator Helper Methods

Mega Challenge Casino

Solution - Mega Challenge Casino

Lesson 35 - Manipulating Strings

Challenge 9 - Phun With Strings

Solution - Challenge Phun With Strings

Lesson 36 - Introduction to Classes and Objects

Challenge - Hero Monster Classes Part 1

Solution - Hero Monster Classes Part 1

Challenge - Hero Monster Classes Part 2

Solution - Challenge Hero Monster Classes Part 2

Lesson 37 - Creating Class Files Creating Cohesive Classes and Code Navigation

Lesson 38 - Understanding Object References and Object Lifetime

Lesson 39 - Understanding the .NET Framework and Compilation

Lesson 40 - Namespaces and Using Directives

Lesson 41 - Creating Class Libraries and Adding References to Assemblies

Lesson 42 - Accessibility Modifiers, Fields and Properties

Lesson 43 - Creating Constructor Methods

Lesson 44 - Naming Conventions for Identifiers

Lesson 45 - Static vs Instance Members

Challenge 10 - Challenge Simple Darts

Solution - Challenge Simple Darts

Lesson 46 - Working with the List Collection

Lesson 47 - Object Initializers

Lesson 48 - Collection Initializers

Lesson 49 - Working with the Dictionary Collection

Lesson 50 - Looping with the foreach Iteration Statement

Lesson 51 - Implicitly-Typed Variables with the var Keyword

Challenge 11 - Challenge Student Courses

Solution - Challenge Student Courses

Mega Challenge War

Solution - Mega Challenge War

Lesson 52 - Creating GUIDs

Lesson 53 - Working with Enumerations

Lesson 54 - Understanding the switch() Statement

Lesson 55 - First Pass at the Separation of Concerns Principle

Lesson 56 - Understanding Exception Handling

Lesson 57 - Understanding Global Exception Handling

Lesson 58 - Understanding Custom Exceptions

Lesson 59 - Creating a Database in Visual Studio

Lesson 60 - Creating an Entity Data Model

Lesson 61 - Displaying the DbSet Result in an ASP.NET GridView

Lesson 62 - Implementing a Button Command in a GridView

Lesson 63 - Using a Tools-Centric Approach to Building a Database Application

Lesson 64 - Using a Maintenance-Driven Approach to Building a Database Application

Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database

Lesson 66 - Package Management with NuGet

Lesson 67 - NuGet No-Commit Workflow

Lesson 68 - Introduction the Twitter Bootstrap CSS Framework

Lesson 69 - Mapping Enum Types to Entity Properties in the Framework Designer

Lesson 70 - Deploying the App to Microsoft Azure Web Services Web Apps

Papa Bob's Mega Challenge

Papa Bob's Mega Solution Part 1 - Setting up the Solution

Papa Bob's Mega Solution Part 2 - Adding an Order to the Database

Papa Bob's Mega Solution Part 3 - Passing an Order from the Presentation Layer

Papa Bob's Mega Solution Part 4 - Creating the Order Form

Papa Bob's Mega Solution Part 5 - Adding Enums

Papa Bob's Mega Solution Part 6 - Creating an Order with Validation

Papa Bob's Mega Solution Part 7 - Calculating the Order Price

Papa Bob's Mega Solution Part 8 - Displaying the Price to the User

Papa Bob's Mega Solution Part 9 - Creating the Order Management Page


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