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C# C# Objects Methods Documentation

Friso Mosselmans
Friso Mosselmans
2,105 Points
Posted by Friso Mosselmans
Friso Mosselmans
2,105 Points

How can I see what type of method "System.DateTime.DaysInMonth()" is? static or instance?

I really don't understand in this quiz why "System.DateTime.DaysInMonth()" is a static method, while "System.DateTime.AddDays()" is an instance method? There is no difference in the way they are called, is there? So how can you tell?

3 Answers

Eduardo Parra San Jose
Eduardo Parra San Jose
12,579 Points

Hi,

One way to know if a method is static or not is too look in the MSDN documentation:

The difference between them is that you can call System.DateTime.DaysInMonth static method, directly from the class, without creating an object:

// The example is from the MSDN documentation for System.DateTime.DaysInMonth
int daysInJuly = System.DateTime.DaysInMonth(2001, July);

However, to call System.DateTime.AddDays you have to create an object of the type DateTime:

// The example is from the MSDN documentation for System.DateTime.AddDays
DateTime today = DateTime.Now;
DateTime answer = today.AddDays(36);

I hope it helps. Have a nice day

Steven Parker
Steven Parker
229,644 Points
Steven Parker
Steven Parker
229,644 Points

:point_right: The difference is clearly indicated in the documentation.

If you look at the documentation pages for System.DateTime.DaysInMonth() and System.DateTime.AddDays() , you can clearly see that the first is defined as "static", while the second is not.

As to why these are implemented differently, you can see that DaysInMonth takes two integer arguments and returns another integer. Since it makes no direct reference to a DateTime object, it makes sense that it would be implemented as static so it can be invoked without requiring a DateTime instance.

On the other hand, since the purpose of AddDays is to modify an existing DateTime object, it must have a reference to a DateTime object instance. So it makes sense that it would be implemented as an instance method.

There is, in fact, a significant difference in the way these are called. Check the documentation pages for examples.

Friso Mosselmans
Friso Mosselmans
2,105 Points
Friso Mosselmans
Friso Mosselmans
2,105 Points

Thank you both for these great answers!