The Daily WTF

Inheritance is one of those object-oriented concepts that creates a lot of conflicts. You’ll hear people debating what constitutes an “is-a” versus a “has-a” relationship, you’ll hear “favor composition of inheritance”, you’ll see languages adopt mix-in patterns which use inheritance to do composition. Used well, the feature can make your code cleaner to read and easier to maintain. Used poorly, it’s a way to get your polymorphism with a side of spaghetti code.

Greg was working on a medical data application’s front end. This representative line shows how they use inheritance:

public class Patient extends JavascriptStringBuilder

Greg writes: “Unfortunately, the designers were quite unacquainted with newfangled ideas like separating model objects from the UI layer, so they gave us this gem.”

This, of course, was a common pattern in the application’s front end. Many data objects inherited from string builder. Not all of them, which only helped to

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