AOP stands for Aspect-Oriented Programming. Use this tag if your question is about aspect-oriented concepts and techniques, or for programming problems using AOP extensions in any language. AOP increases modularity by allowing the separation of "cross-cutting concerns" into aspects. Click learn more... to find out what it's all about.
AOP stands for aspect-oriented programming. Questions about aspect-oriented concepts, techniques, and programming problems using AOP extensions in any language should have this tag.
AOP exists because there are two types of requirements in software engineering: functional requirements (concerns) describe specific behaviors; non-functional requirements (cross-cutting concerns) describe general qualities or services. In OOP, concerns are implemented in a very modular way -- all of the code for a concern is kept together, usually in a class. This is a good thing because modular code increases software quality.
However, cross-cutting concerns cannot be modularized in OOP (that's why they're called "cross-cutting" because they 'cut across' the functional concerns). Code for a cross-cutting concern ends up being spread out (tangled) over many, or even all, of the modules in an OOP program. AOP fixes this problem by collecting that spread-out code into one module called an aspect.
Logging, caching, security, and transaction management are examples of cross-cutting concerns. AOP makes it straightforward to retrofit existing applications with any of these services. The original code is not modified. Instead, an aspect is created with advice and pointcuts. Advice is like a class method - it contains code with the new functionality to be added. A pointcut is code that selects one or more join points. Join points are specific places in the existing program where the advice will be applied. The new program is created during a process called weaving, when the original code and the aspect code are integrated with each other. Weaving can be done at compile-time or load-time, so you can add aspects to programs even when you don't have the source code (there are some restrictions, see here for example).
The most widely used AOP language is AspectJ, which is an aspect-oriented enhancement to Java. Using AOP in the Spring framework is also popular here on SO. AOP is accessible in a number of ways including command-line, Eclipse, Spring, and IntelliJ Ultimate. AOP is also available for several other languages: Python, JavaScript, Ruby, Lua, and Smalltalk.
AOP was first used in 1997 at Xerox PARC to solve the problem of tangled cross-cutting concerns in object-oriented programs.
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