Question

I have a class that requires a specific method to be called before being used by other objects, this method implements all the required logic and sets the properties of the class to their respective values. How can I ensure that the method of this class is called before the object is returned for use by other objects? I heard that it is a bad idea to implement logic in the constructor so I cannot call this method in the constructor. A code example for this sort of implementation is as follows:

SomeClass myClass = new SomeClass("someName");
//Class must call this method if object is to be of any use
myClass.ConvertNameToFunnyCharacters();
return myClass;

Answer 1

Putting a lot of logic in the constructor can lead to a few problems:

• If the constructor calls methods of the object, those methods run in a partially constructed object. This can really bite you when you override the method in subclasses: in Java and C# the subclass’ implementation will run before the subclass’ constructor has initialised the extended state of the object and so fail with null pointer exceptions. C++ works more “correctly” but can cause different confusing effects.
• It makes unit testing with mock objects a bit more complicated if the constructor calls back out to objects passes as parameters.

So, I prefer to keep constructors as simple as possible: just assign parameters to instance variables. If I need to perform more complex logic to initialise an object I write a static factory function that calculates the constructor parameter values and passes them to a simple constructor.