C#•2y ago

❔ ✅ public class

55 Replies

Ryan-T1412OP•2y ago

class is already public why do we use public for every fields and methods

Saber•2y ago

so you can access them from outside of the class

Ryan-T1412OP•2y ago

but is there another way? using public ones

cap5lut•2y ago

there are different visibility modifiers, public, internal, protected and private i wont get into detail for all all them to keep it simple and understandable. i will take the Human class as base for my explanation:

public class Human
{
  public int Age;
}

public class Human
{
  public int Age;
}

an age of 65 would be fine as value. but no human should be -100 years old, right? thats why u have mechanisms set the age only if its a valid value:

public class Human
{
  private int _age;
  public int Age
  {
    get
    {
      return _age;
    }
    set
    {
      if (value < 0 || value > 150) throw new ArgumentException("Invalid age!")
      _age = value;
    }
  }
}

public class Human
{
  private int _age;
  public int Age
  {
    get
    {
      return _age;
    }
    set
    {
      if (value < 0 || value > 150) throw new ArgumentException("Invalid age!")
      _age = value;
    }
  }
}

here its declared that u must be at least 0 years old (new born) or at maximum 150 years old, so everything lower than zero or higher than 150 should complain the actual value is stored in _age, which is has the private visibility modifier and thus is only accessible in this very own class the Age property is publicly accessable, well.... to have public access to the age of a human basically the modifiers are used to keep that human in the "correct state" at any time u interact with it. if u could do someHuman._age = -123; that would lead to someHuman having an invalid state as no human should be younger than freshly born in the case this was too complex for u, here is another human example: for humans we want to have 2 functionalities: let them eat and let them say how much they ate yet so 2 methods are needed Eat() and SayHowMuchYouAte():

public class Human
{
  public void Eat()
  {
    Console.WriteLine("Eating");
  }
  public void SayHowMuchYouAte()
  {
    Console.WriteLine("I ate ??? times.");
  }
}

public class Human
{
  public void Eat()
  {
    Console.WriteLine("Eating");
  }
  public void SayHowMuchYouAte()
  {
    Console.WriteLine("I ate ??? times.");
  }
}

the ??? must be replaced with the actual count, which means we need to introduce a counter variable: and to raise it when we eat:

public class Human
{
  public int _eatCounter = 0; // this is the counter

  public void Eat()
  {
    _eatCounter = _eatCounter + 1; // we eat, so we increase the counter
    Console.WriteLine("Eating");
  }
  public void SayHowMuchYouAte()
  {
    Console.WriteLine("I ate {0} times.", _eatCounter); // just trust me that it prints something like "I ate 13 times."
  }
}

public class Human
{
  public int _eatCounter = 0; // this is the counter

  public void Eat()
  {
    _eatCounter = _eatCounter + 1; // we eat, so we increase the counter
    Console.WriteLine("Eating");
  }
  public void SayHowMuchYouAte()
  {
    Console.WriteLine("I ate {0} times.", _eatCounter); // just trust me that it prints something like "I ate 13 times."
  }
}

now think about this code:

Human someHuman = new Human();
someHuman.Eat();
someHuman.Eat();`
someHuman.SayHowMuchYouAte();

Human someHuman = new Human();
someHuman.Eat();
someHuman.Eat();`
someHuman.SayHowMuchYouAte();

that would print

Eat
Eat
I ate 2 times.

Eat
Eat
I ate 2 times.

but because _eatCounter is public, u can modify it:

Human someHuman = new Human();
someHuman.Eat();
someHuman._eatCounter = 0;
someHuman.Eat();
someHuman.SayHowMuchYouAte();

Human someHuman = new Human();
someHuman.Eat();
someHuman._eatCounter = 0;
someHuman.Eat();
someHuman.SayHowMuchYouAte();

that would print

Eat
Eat
I ate 1 times.

Eat
Eat
I ate 1 times.

which is a lie! the _eatCounter should be private, so that only from within itself it can be accessed and modified for different circumstances different modifiers exist. public and private are the easiest to explain so i sticked to them for this explanation. there is a lot more under the hood u will learn later 😉

Ryan-T1412OP•2y ago

why did you use _

cap5lut•2y ago

sorry for that wall for text

Ryan-T1412OP•2y ago

before variable names

cap5lut•2y ago

_variableName is a naming convention for private members basically the moment u see the _ in front of the name -> its a private member

Ryan-T1412OP•2y ago

thanks for everything 🙂

cap5lut•2y ago

public int _eatCounter = 0; would be bad as its not private, it should be private int _eatCounter = 0;

Ryan-T1412OP•2y ago

there are too much thing that i don't know

cap5lut•2y ago

do not care too much about that yet, you are a beginner after all 😉

Ryan-T1412OP•2y ago

and this '??? '

cap5lut•2y ago

thats just a placeholder for my explanation

Ryan-T1412OP•2y ago

oh i got it sorry

cap5lut•2y ago

Console.WriteLine("I ate {0} times.", _eatCounter); <- this replaces the {0} with the value of _eatCounter the ??? was just to not have to explain it xD but more importantly, do u understand the difference between public and private?

Ryan-T1412OP•2y ago

why is _eatCounter public

cap5lut•2y ago

thats the correct question! short answer: it should NOT be public. long answer:

the _eatCounter should be private, so that only from within itself [the class] it can be accessed and modified

Ryan-T1412OP•2y ago

perfect it's like global scope and local scope right

cap5lut•2y ago

sort of, yes

Ryan-T1412OP•2y ago

i can't access a private variable outside of the class

Unknown User•2y ago

Message Not Public

cap5lut•2y ago

yeah object basically has its internal state (private members) and a public interface to interact with it in this example only one state was there _eatCounter. but imagine u have additional counters, like how often vegetables were eaten or how often meat. for that u might have a method like EatASteakWithCucumbers() where u would have to increment two of many members (dont take my culinary knowledge into account here xD) anyway, i think you grasped how visibility modifiers work. dont be too concerned about them for now and keep going

Ryan-T1412OP•2y ago

what about "static" keyword is it complicated?

cap5lut•2y ago

its not really complicated if u understand it xD let me think how to explain it (you can give ur thoughts on it meanwhile) (ill need 1-3min for my ciggy)

Ryan-T1412OP•2y ago

sure 🙂

Unknown User•2y ago

Message Not Public

MODiX•2y ago

In C#, static allows you to have members (classes, methods, etc) that are not tied to any particular instance and are therefore always, globally, accessible. When applying static members, take the following considerations: • If there are to be multiple instances of a class, do not use static • If you need to track state, do not use static • If you are going to have multi threaded workflows, do not use static unless you're aware of the caveats static is best used for stateless methods, extension methods/classes and in areas where you understand the pros/cons. Read more here: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/static

cap5lut•2y ago

do u the difference between a type (class) and an instance? (trying to figure out how to explain it)

Ryan-T1412OP•2y ago

hmm, classes for similar group of objects but instances are more specific is that what you were asked?

cap5lut•2y ago

do u know anything about inheritance yet?

Ryan-T1412OP•2y ago

nope

cap5lut•2y ago

okay, then it will be hard 😂 classes describe a certain functionality, like the Human from before Human is a type, basically like a "blue print" that describes some features (in our case the eating counter) but its just a blue print, it doesnt describe an individual human

Ryan-T1412OP•2y ago

i think i understand inheritance it's like there is a main class

cap5lut•2y ago

dont get too stuck on inheritance

Ryan-T1412OP•2y ago

ok i can't explain what i understand

cap5lut•2y ago

if u cant explain what ya understand, u dont understand it ;p (that goes for me as well!)

Ryan-T1412OP•2y ago

public class Animal
{
    public string Name { get; set; }
    public int Age { get; set; }

    public virtual void MakeNoise()
    {
        Console.WriteLine("Some generic animal noise");
    }
}

public class Dog : Animal
{
    public string Breed { get; set; }

    public override void MakeNoise()
    {
        Console.WriteLine("Woof!");
    }
}

public class Cat : Animal
{
    public string FurColor { get; set; }

    public override void MakeNoise()
    {
        Console.WriteLine("Meow!");
    }
}

public class Animal
{
    public string Name { get; set; }
    public int Age { get; set; }

    public virtual void MakeNoise()
    {
        Console.WriteLine("Some generic animal noise");
    }
}

public class Dog : Animal
{
    public string Breed { get; set; }

    public override void MakeNoise()
    {
        Console.WriteLine("Woof!");
    }
}

public class Cat : Animal
{
    public string FurColor { get; set; }

    public override void MakeNoise()
    {
        Console.WriteLine("Meow!");
    }
}

here is an example

cap5lut•2y ago

okay, u only had problems phrasing it, thats okay ;p

Ryan-T1412OP•2y ago

my english is bad 😄

cap5lut•2y ago

tbh, ill take ur code as example to explain static

Ryan-T1412OP•2y ago

ok it's not actually mine but yeah haha good example tho

cap5lut•2y ago

well the code u posted i mean xD

Ryan-T1412OP•2y ago

okk

cap5lut•2y ago

sorry i really have a hard time rn how to explain it 😒

Ryan-T1412OP•2y ago

not a problem thanks for being helpful it's 6:20 in the morning and i gotta sleep

cap5lut•2y ago

4:20am here ;p

Ryan-T1412OP•2y ago

oh good night then

cap5lut•2y ago

uhm, ill keep it simple for now imagine if ya want a method that returns either a Dog or a Cat instance, based on if the user input is "dog" or "cat" (both would be simple strings) where would u place that method?

Ryan-T1412OP•2y ago

animal 😄

cap5lut•2y ago

oh damn, i have over complicated it: imagine you have class reflecting the age of a human:

public class Age
{
  public static int MinAge = 0;
  public static int MaxAge = 150;

  // instance members
  private int _value;
}

public class Age
{
  public static int MinAge = 0;
  public static int MaxAge = 150;

  // instance members
  private int _value;
}

Ryan-T1412OP•2y ago

yep

cap5lut•2y ago

the difference betewwn MinAge and _value is quite simple: MinAge is a global thingy for Age (the type), _value is a (non-static) value for its own specific instance basically static is something directly "attached" to Age the type, while _value is something "attached" to an instance/object of the type Age taken this definition of the class:

public class Age
{
  public static int MinAge = 0;
  public int Value;
}

public class Age
{
  public static int MinAge = 0;
  public int Value;
}

and this code:

Console.WriteLine(Age.MinAge); // global
Console.WriteLine(Age.Value); // local; this will error because its not static

Age instance = new Age();
instance.Value = 21; // this isnt erroring because its on an instance
Console.WriteLine(instance.Value);

Console.WriteLine(Age.MinAge); // global
Console.WriteLine(Age.Value); // local; this will error because its not static

Age instance = new Age();
instance.Value = 21; // this isnt erroring because its on an instance
Console.WriteLine(instance.Value);

basically static is "global" to the type, and the other is instance based ill hit the sack for now, but once i arise ill respond if ya wrote something

Ryan-T1412OP•2y ago

nice example even if i understand it 😄 thank you dude !close

Accord•2y ago

Closed! Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ ✅ public class