Lära Class Objects | Introduction to Object-Oriented Programming (OOP)

An object of a class can be created using the following syntax:

index.cs


              1
            
className variableName = new className();

We can access the field of a class using the dot (.) operator:

index.cs


              1
            
variableName.fieldName

For-example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player p1= new Player();
        
        p1.username = "Don";
        Console.WriteLine(p1.username);
    }
}

The expression new Player(); is used for creating a new object while Player p1 is used for creating a variable for storing that new object. So simply writing Player p1; will only create an empty variable with no object inside it therefore we have to create a new object and, in turn, store it into a variable: Player p1 = new Player();.

Therefore, if we create an Array of size 10 using the Player class, it won't create 10 objects, rather, it will create an empty array with a capacity to store 10 Player objects. This can be understood by the following example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        
        players[0].username = "Don"; // Error on this line
        Console.WriteLine(players[0].username);
    }
}

The error says "Object reference not set to an instance of an object" which simply means that we are trying to access data from an object that is not there - there is no object to access at the index 0.

This can be fixed by manually creating an object at the index 0:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        players[0] = new Player();
        players[0].username = "Don";
        Console.WriteLine(players[0].username);
    }
}

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An object of a class can be created using the following syntax:

index.cs


              1
            
className variableName = new className();

We can access the field of a class using the dot (.) operator:

index.cs


              1
            
variableName.fieldName

For-example:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player p1= new Player();
        
        p1.username = "Don";
        Console.WriteLine(p1.username);
    }
}

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        
        players[0].username = "Don"; // Error on this line
        Console.WriteLine(players[0].username);
    }
}

This can be fixed by manually creating an object at the index 0:

index.cs


              12345678910111213141516
            
using System;

class Player {
    public string username;
}

public class ConsoleApp
{
    public static void Main(string[] args)
    {
        Player[] players = new Player[10];
        players[0] = new Player();
        players[0].username = "Don";
        Console.WriteLine(players[0].username);
    }
}

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 3. Kapitel 4

Class Objects

Awesome!

Class Objects