Static in C# - Part 1

What is static?

Based on Microsoft (father of C-Sharp), it is modifier to declare a static member, which belongs to the type itself rather than to a specific object. For example, class have structure following:

class Test(){
    public string Content;
}

In main function, we have:

static void Main(string[] args){
    var t1 = new Test() { Content = "Test 1" };
    var t2 = new Test() { Content = "Test 2" };

    Console.WriteLine(t1.Content); //output: Test 1
    Console.WriteLine(t2.Content); // output: Test 2
}

So we can see the output will difference with other instance. But if we use static in class, what happen?

class Test(){
    public static string Content;
}

And update in main function:

static void Main(string[] args){
    var t = new Test() { };

    //error here because you can't access static property through by instance
    Console.WriteLine(t.Content); 

    Test.Content = 'Static Content'
    Console.WriteLine(Test.Content); //output: Static Content

    ChangeContent("Update content with function");
    Console.WriteLine(Test.Content); //output: Update content with function
}

static void ChangeContent(string content)
{
    Test.Content = content;
}

Compare main before and after, we have table conclusion:

	Non static	Static
Create at	New instance create	Compiler time
Access by	Instance	Class
Value	Follow the instance	Follow the class
Life time	Until the instance deallocate	Until program end

P/s: With static keyword, the variable will be stored in heap memory, below is short description about stack & heap:

	Stack	Heap
Store	- Primitive type - Reference variable - Function call	- Object - Static type
Structure	Last In First Out (LIFO)	Dynamic
Performance access	Faster	Slower