Type hierarchy

Hi Alan,

First of to clarify some things: Every Exception is of Type System.Exception.

catch(System.Exception ex) { }

This block will search for an Exception of Type System.Exception which is every Exception. Based on this we can say which exceptions a catch block will catch and which not.

An arguments or variables type must be more general then the Instance it is capturing

Object alan = new Person("Alan"); // obj is more general (is the parent class of Person) then the Person class
Person alan = new Object(); // will not work because Person Type is more specific

The same for method parameters, properties (...) and of course, catch blocks and there arguments: If the thrown Exception is more specific then the type passed to the catch block it will catch it.

try {
    throw new OtherException("This exception is based on NewException which is on itself based on System.Exception");
}
catch(NewException nEx) {
   // Exception will be caught here because OtherException is more specific than NewException
}
catch(Exception ex) {
 // Every Exception which is not based on NewException (because those are already handled by the above block) will be handled here
}

Now back to your question.

• TreehouseDefense.OutOfBoundsException is based on TreehouseDefense.TreehouseDefenseException -> Which is why it is catch by it in question 3.

    try
    {
        DoSomething(); // throws TreehouseDefense.OutOfBoundsException
    }
    catch(TreehouseDefense.TreehouseDefenseException ex)
    {
    }
    catch(System.Exception ex)
    {
    }

• TreehouseDefense.TreehouseDefenseException is based on System.Exception

In question 5 the more general Exception is thrown (TreehouseDefense.TreehouseDefenseException) so the catch with the more specific type will let it pass.

It would catch it if the passed in Type is more general then the thrown Exception

try
    {
        DoSomething(); // throws TreehouseDefense.TreehouseDefenseException which is more specific then System.Exception
    }
    catch(Exception ex) // is most general Exception Type
    {
    }

In this and every other case the exception would be caught.

Hope this helps;