AspectJ(tm) is a simple and practical extension to the Java(tm) programming language that adds to Java aspect-oriented programming (AOP) capabilities. AOP allows developers to reap the benefits of modularity for concerns that cut across the natural units of modularity. In object-oriented programs like Java, the natural unit of modularity is the class. In AspectJ, aspects modularize concerns that affect more than one class.
You compile your program using the AspectJ compiler (perhaps using the supported development environments) and then run it, supplying a small (< 100K) runtime library.
The AspectJ technologies include a compiler (ajc), a debugger (ajdb), a documentation generator (ajdoc), a program structure browser (ajbrowser), and integration with Eclipse, Sun-ONE/Netbeans, GNU Emacs/XEmacs, JBuilder, and Ant.