An introduction to Aspect Oriented Programming – AspectJ

As I have been finding in my research, software modularity is crucial to maintainable, separable code. Sadly in modern times, Object Oriented Programming though allowing for common class related code to be modularised, it lacks the modularity needed to avoid code scattering (you know when you have some type of functionality found in parts all over a program) and code tangling (when you have different aspects of your program all mixed up in a single method). Anyhow, this is where the use of Aspect Oriented Programming can come in handy. Aspect-Oriented Programming is based around the idea of modularising “aspects” of your program into their own modules, called Aspects (you was expecting that wasn’t you?).

Common examples to how this can be useful is normally in the situations of say security: On particular class methods you need to do some sort of security checks.  Now in OOP, you would probably have this tangled and scattered across all the classes which require this checking. Though at first may feel normal, what happens when you want to alter the security checking? You need to go through all the classes/methods affected, wasting time (which otherwise can be wasted on facebook).

In this post I will be going through a simple example of AspectJ, an AOP extension to Java.

Firstly, to use aspectj you need to download the tools, these can be for a number of IDEs but I recommend the eclipse plugin ( Once the plugin is installed and enabled we are all set and ready to begin.

Starting a new AspectJ Project

Once you have the development tools installed and enabled, we will start by starting a new AspectJ project. For this you may find it isn’t in the menu when clicking on “new”, so click on other. We setup normal Java project settings and make a very basic HelloWorld program.


Now, for this example I will work with an aspect called “Logger”. The beauty of AOP is being able to crosscut concerns (code tangling and scattering). For instance, if you updating security aspects of your program that were involved all over your program, you would have these parts in lots of different methods, making it difficult to track. With AOP, you can put all these concerns within a single aspect, needing to edit/update that single aspect file…simple!

Within the aspect, we now first specify the pointcut (where do you want to apply advice) in line 8. Then you want to then want to program what advice you want it to execute and when (before, around, or after the pointcut). As you see in the second screenshot, the string ” Aspect” is appended to the string “Hello World” already outputted.

I strongly suggest after trying this simple example you experiment with other more complex examples. In the next post I will tell you guys how this method can be integrated and used within Android programming as an alternative programming paradigm to OOP.

Until next time!

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