Skip to main content

Dynamic Traits with Java

Traits are reusable components representing a set of methods or behaviors that can be used to extend the functionality of multiple classes. Some programming languages like Groovy and Scala have been supporting Traits for a long time, and allow dynamic association of Traits to any object, at runtime.

Java being a strongly typed programming language, enforces a very strict discipline of type association, upfront whilst declaring any language element, e.g. variables, functions, etc; and the same is applicable for Classes too. Therefore when you implement a class in Java, the associative types for the class, must be specified as a part of the declaration of the class, which strongly binds the type interfaces to the class, and cannot be changed in runtime.

The concept of Traits is implemented in Java using Interfaces, which contain default methods and variables to allow maintaining an object's state. However, these interfaces then have to be tightly coupled with the class declaration, and as discussed above one cannot dynamically modify an interface association.

Java-DynaTraits is a very simple and minimalist library, that allows dynamic association of Traits/Interfaces; such that new interfaces could be added to your class at runtime, without really having to specify them, with the declaration of the class.

The core concept behind the code is to use a subscription model, which allows registering interfaces (or in other words Traits) with a class, in runtime, and then using an Invocation Handler to delegate function calls to the relevant subscriptions.

An Example Code

Following is a sample code, that demonstrates an example usage -


var catalog = (CatalogInterface & NamedEntity & PricedEntity) 
(new Catalog()).withTraits(new NamedEntity(){}, new PricedEntity(){});

// The setName function is rendered by the "NamedEntity" trait.
catalog.setName("Dynamic Traits with Java");
System.out.println(catalog.getName());

// The setPrice function is rendered by the "PricedEntity" trait
catalog.setPrice(20.00);
System.out.println(catalog.getPrice());


Please visit the project page on Github for further details.

Comments

Post a Comment

Popular posts from this blog

Shard – A Database Design

Scaling Database is one of the most common and important issue that every business confronts in order to accommodate the growing business and thus caused exponential data storage and availability demand. There two principle approaches to accomplish database scaling; v.i.z. vertical and horizontal. Regardless of which ever scaling strategy one decides to follow, we usual land-up buying ever bigger, faster, and more expensive machines; to either move the database on them for vertical scale-up or cluster them together to scale horizontally. While this arrangement is great if one has ample financial support, it doesn't work so well for the bank accounts of some of our heroic system builders who need to scale well past what they can afford. In this write-up, I intend to explain a revolutionary and fairly new database architecture; termed as Sharding, that some websites like Friendster and Flickr have been using since quite sometime now. The concept defines an affordable approach t...
8 comments
Read more

FAINT - Search for faces

Lately, I've been playing around a bit with facial pattern recognition algorithms and their open source implementations. I came across many reference implementation but a very few were implemented in Java, and the Eigenfaces algorithm by far happens to be the best amongst them all. During my research around the said topic i happened to stumble-upon an implementation called FAINT (The Face Annotation Interface - http://faint.sourceforge.net). Faint by far the best facial pattern recognition API and as you must have already guessed, it implements the Eigenfaces algorithm. Now enough of theory talks, how about implementing an example with faint...? Here is one for all you face-recognition enthusiasts. The following example simply searches for faces in a given photograph and thumbnails them. Now, I know thats not face recognition; but be a little creative here. Once you have the facial thumbnails extracted, its never a big deal to look further in the Faint API and find methods which ca...
27 comments
Read more

Is Java String really immutable...?

In many texts String is cited as the ultimate benchmark of Java's various immutable classes. Well, I'm sure you'd have to think the other way once you have read this article. To start with, let's get back to the books and read the definition of immutability. The Wikipedia defines it as follows - 'In object-oriented and functional programming, an immutable object is an object whose state cannot be modified after it is created.' I personally find this definition good as it mentions that an immutable instance's state should not be allowed to be modified after it's construction. Now keeping this in the back of our minds, let's decompile Java's standard String implementation and peep into the hashCode() method - public int hashCode() { int h = hash; if (h == 0) { int off = offset; char val[] = value; int len = count; for (int i = 0; i h = 31*h + val[off++]; } hash = h; } return h; } A detailed ...
2 comments
Read more