When I first laid eyes on Java 8’s Stream API and found out that it worked lazily (then found out what that meant), I was blown away and utterly baffled. It didn’t seem possible at all. Eventually, I was able to wrap my head around it, realizing it was done with my favorite design pattern: the Decorator Pattern!
In this post, I’m going to go through and write up a simplified implementation, only going through the
reduce() methods. We’ll also be ignoring the ability to parallelize the calls. Lastly, for the sake of readability, I’ll be ignoring
extends in the generics. Continue Reading
Back in my delegate decorator article, I mentioned some weaknesses of the delegate pattern as a substitute to inheritance. The decorator solved one of those problems, but the other is still a problem. The problem comes when using something akin to the template pattern. Continue Reading
Recently, I posted about how you can use composition instead of inheritance, and in that article, I mentioned the Delegate Pattern. As a quick description, the pattern has you inherit from the parent interface (or, in Python, you can just implement the protocol), but all the methods either redirect to calling the method on an injected implementation of interface/protocol, possibly surrounding the call in its own code, or it completely fills the method with its own implementation.
For the most part, it is like manually implementing inheritance, except that the superclass in injectable.
Anyway, one of the more annoying parts of implementing the Delegate Pattern is having to write all of the delegated calls. So I decided to look into the possibility of of making a decorator that will do that for you for all the methods you don’t explicitly implement. Continue Reading
Quite a while back, I posted about how, despite the fact that you should prefer composition over inheritance, you can best design classes for inheritance. Now, I wish to give some examples of how you can take your code that uses inheritance and change it to use composition instead, which will often actually make your code more flexible.
The code will be in java, but the concepts can transferred to any language that is object-oriented. Some languages might have constructs that make parts of this easier, too (Kotlin’s Delegates).
One thing is important to remember, though: Even if you switch “completely” to composition, you will still have some inheritance. This inheritance will be from interfaces and interface-like classes only, though. It barely counts as inheritance, really, since all it’s doing is restricting itself to an API and not inheriting implementation details. Continue Reading