Editing AspectJ (section)

==Simple language description==
All valid Java programs are also valid AspectJ programs, but AspectJ lets programmers define special constructs called ''[[Aspect-oriented software development#Aspects|aspects]]''. Aspects can contain several entities unavailable to standard classes. These are:

;[[Extension method]]s: Allow a programmer to add methods, fields, or interfaces to existing classes from within the aspect. This example adds an <code>acceptVisitor</code> (see [[visitor pattern]]) method to the <code>Point</code> class:

:<syntaxhighlight lang="aspectj">
aspect VisitAspect {
  void Point.acceptVisitor(Visitor v) {
    v.visit(this);
  }
}
</syntaxhighlight>

;[[Pointcut]]s: Allow a programmer to specify join points (well-defined moments in the execution of a program, like method call, object instantiation, or variable access). All pointcuts are expressions ([[Aspect-oriented software development#Quantification and obliviousness|quantifications]]) that determine whether a given join point matches. For example, this point-cut matches the execution of any instance method in an object of type <code>Point</code> whose name begins with <code>set</code>:

:<syntaxhighlight lang="aspectj">
pointcut set() : execution(* set*(..) ) && this(Point);
</syntaxhighlight>

;[[Advice (programming)|Advices]]: Allow a programmer to specify code to run at a join point matched by a [[pointcut]]. The actions can be performed ''before'', ''after'', or ''around'' the specified join point. Here, the advice refreshes the display every time something on <code>Point</code> is set, using the pointcut declared above:

:<syntaxhighlight lang="aspectj">
after () : set() {
  Display.update();
}
</syntaxhighlight>

AspectJ also supports limited forms of pointcut-based static checking and aspect reuse (by inheritance). See the [http://www.eclipse.org/aspectj/doc/released/progguide/index.html AspectJ Programming Guide] for a more detailed description of the language.