#Java annotations software#
#Java annotations code#

Yes, the compiler checks that you got the name of the annotation right, that you are specifying all the right parameters and that the target (class/method/…) is correct. Going further, the annotation mini-language offers very limited type-safety. This language is very limited, but it’s also an asset: it makes annotations static and enables compile-time or run-time inspection. No expressions, no conditionals, no loops the annotation language shares only basic syntax with Java, otherwise is completely parallel. You can define annotations with parameters, but the parameter values must be constants like Strings, Ints, Class references, arrays of the above, or might be nested annotations. Annotations as a languageįrom a language design perspective, annotations form a mini-language embedded in Java. Let’s explore in more detail which aspects of annotations aren’t the best fit for their current use-cases. Or rather, annotations have found applications far beyond the original intentions of the authors. The design of annotations isn’t without flaws. Hence, whatever other approach we might want to take instead of annotations, it needs to enable a concise and elegant way of describing our classes, data structures and methods, so that it’s possible to inspect them programmatically. Annotations, due to their constrained syntax, can be inspected statically by tools and thanks to the reflection API, the same is possible at run-time.įor example, at application start-up, it’s possible to read the meta-data defined by annotations on any class/method/field, and initialize appropriate business logic statically, without even instantiating the classes involved. despite the separation, meta-data is still part of the codebase, “close” to the referenced elementsīut attaching meta-data is only one side of the equation it would be useless without a way to consume that meta-data and act basing on it.the meta-data is clearly separated from the definition of a class, method or field.They are well-designed in a number of aspects: xml, but annotations are much better suited for this task. This core requirement of attaching meta-data can be satisfied using e.g.

#Java annotations software#

Turns out that to write good software (for many definitions of that term) we simply need a way to describe our classes, data structures and methods.

#Java annotations code#

The most important feature of annotations is what they’ve been designed for: the ability to attach additional information to various fragments of the code we write. Thirdly and finally, knowing the crucial features of annotations, and their shortcomings, we’ll be able to explore the land of possible alternatives.

Such extensions are not type-safe, usually not composable and hard to inspect, reason about and explore. This, in turn, allows you to extend the base language (Java), which is so useful because of Java’s shortcomings. They form an embedded mini-language, interpreted at runtime.

Secondly, however successful, annotations encourage certain design elements, which might be problematic. What are their core characteristics? What are they enabling, that core Java does not? The first question that comes to mind is what is it about annotations that makes them so widely used? Entity mapping, defining REST endpoints, validation, JSON mapping are just a few examples of areas where annotations dominate. To take a good look around, identify our problems, and be able to take a peek beyond the nearest hill, we’ll proceed in three steps.