What to do when construction fails?

Posted on 1998-06-29
Medium Priority
Last Modified: 2010-04-01
Lets say I have a constructor that does some operations, for some reason one or more of these operations fail.  What is the best way to set some sort of error condition?  

A a = new A("filename");

say the filename doesn't exist, now probably any operation I do with a will also fail.  Do I use exceptions?  Add a class function to check for valid creation?

I am not dealing with IO in any sort in my situation, just using it to clearify my problem
Question by:micah
LVL 15

Accepted Solution

Tommy Hui earned 400 total points
ID: 1166887
Yes, you have two choices:

1. throw an exception and expect the client of the class to catch any possible exceptions.

2. Put the state of the object into an error state so that any methods called will be an error. Also you may need to provide a GetState() accessor to determine if the object is in an error state or not. This requires the client to consciously to call the GetState() method to determine if the class is valid or not.

I would opt for the first one if you have access to all of the client's code simply because it is typically unlikely for the exception to occur and hence the amount of code necessary to change will be quite local.

In the second case, it requires more changes because each time a method is called, the state of the object needs to be checked.

LVL 22

Expert Comment

ID: 1166888
There is actually a third choice, but I would probably opt for one of the others.  But the third choice is you can return an error code of some sort using a reference parameter.

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