few questions about this video.

Question

hi, Im not fully understand why we created the Exception.cs file in the first place? for what purpose?

another question is, in this example the teacher write this code :

 class TreehouseDefenseException : System.Exception
    {
         public TreehouseDefenseException()
            {
            }


        public TreehouseDefenseException(string message) : base(message)
        {

        }

    }

    class OutOfBoundsException : TreehouseDefenseException
    {
        public OutOfBoundsException()
        {
        }


        public OutOfBoundsException(string message) : base(message)
        {
        }
    }
}

TreehouseDefenseException inherits from the system.exception, But why after that "OutOfBoundsException inherits TreehouseDefenseException?

another thing i dont fully understand is the meaning of "base" why in this example we passed ":base(message) 2 times?

Steven Parker

Answer 1 · 2018-11-30T14:24:18Z

November 30, 2018 2:24pm

First the point of creating TreehouseDefenseException and all is to show you an example of how to extend the Exception class and create your own exceptions. The 'in code' reason is to be able to differentiate this type of exception from other Exceptions that may be thrown by the system or other projects. Also it gives you the ability to handle this specific type of exception differently when you are setting up a try-catch block. So for example if only for TreehouseDefenseException you just wanted to log the error and continue running, but normal exceptions you wanted to display a message to the user.

try
{
   //some code that may throw either a TreehouseDefenseException or some other Exception

} catch(TreehouseDefenseException tdex) {
   //just log error
}catch(Exception ex) {
   //display some message to the user
}

As far as why OutOfBoundsException inherits TreehouseDefenseException, it seems the idea here is to begin creating a list of custom exceptions that are all identified as being thrown by the Treehouse Defense code, so that these exceptions can be handled differently that regular system exceptions. (again aside from the educational purpose)

The base() call is used in the method signature of a constructor when you want to send a parameter to the constructor of the parent class. It is used twice in this code because there are 3 levels of exceptions. So whenever a new OutOfBoundsException is created and thrown a message parameter can be sent into the constructor (though not required since there is a default constructor), after any code in the constructor method is run, the same message parameter is passed up to the constructor of the TreehouseDefenseException class through the base(message) call. Then the same thing happens in TreehouseDefenseException to pass the same message parameter up to the top parent class's constructor System.Exception.

Hope this helps. Please let me know if I can clarify anything. And happy coding :)

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few questions about this video.

Steven Parker

Steven Parker

1 Answer

Allan Clark

Allan Clark

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