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Organizing Data
These refactoring techniques help with data handling, replacing primitives with rich class functionality.
Another important result is untangling of class associations, which makes classes more portable and reusable.
Problem: You use direct access to private fields inside a class.
Solution: Create a getter and setter for the field, and use only them for accessing the field.
Problem: A class (or group of classes) contains a data field. The field has its own behavior and associated data.
Solution: Create a new class, place the old field and its behavior in the class, and store the object of the class in the original class.
Problem: So you have many identical instances of a single class that you need to replace with a single object.
Solution: Convert the identical objects to a single reference object.
Problem: You have a reference object that’s too small and infrequently changed to justify managing its life cycle.
Solution: Turn it into a value object.
Problem: You have an array that contains various types of data.
Solution: Replace the array with an object that will have separate fields for each element.
Problem: Is domain data stored in classes responsible for the GUI?
Solution: Then it’s a good idea to separate the data into separate classes, ensuring connection and synchronization between the domain class and the GUI.
Problem: You have two classes that each need to use the features of the other, but the association between them is only unidirectional.
Solution: Add the missing association to the class that needs it.
Problem: You have a bidirectional association between classes, but one of the classes doesn’t use the other’s features.
Solution: Remove the unused association.
Problem: Your code uses a number that has a certain meaning to it.
Solution: Replace this number with a constant that has a human-readable name explaining the meaning of the number.
Problem: You have a public field.
Solution: Make the field private and create access methods for it.
Problem: A class contains a collection field and a simple getter and setter for working with the collection.
Solution: Make the getter-returned value read-only and create methods for adding/deleting elements of the collection.
Problem: A class has a field that contains type code. The values of this type aren’t used in operator conditions and don’t affect the behavior of the program.
Solution: Create a new class and use its objects instead of the type code values.
Problem: You have a coded type that directly affects program behavior (values of this field trigger various code in conditionals).
Solution: Create subclasses for each value of the coded type. Then extract the relevant behaviors from the original class to these subclasses. Replace the control flow code with polymorphism.
Problem: You have a coded type that affects behavior but you can’t use subclasses to get rid of it.
Solution: Replace type code with a state object. If it’s necessary to replace a field value with type code, another state object is “plugged in”.
Problem: You have subclasses differing only in their (constant-returning) methods.
Solution: Replace the methods with fields in the parent class and delete the subclasses.