CS 541 Meeting -*- Outline -*-

* Examples of AspectJ

  Use the command line tools and Eclipse to show how to program

   Main reference (esp. for examples):
    AspectJ Progrmmer's guide
    See also AspectJ in Action by Ramnivas Laddad (Manning).

** Basic tool use and join point model example

*** Command line tools

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       COMMAND LINE TOOLS

$ cd joinpoints
$ ajc *.java
$ java Test

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        The -argfile option can be used to name particular file,
         in some order

        ajc -argfile billing.lst 

        CLASSPATH needs to include InstallDir/lib/aspectjrt.jar

*** Eclipse IDE

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        USING ECLIPSE

$ eclipse

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        show how to start a project,
        import files
        build,
        run

        Look at the code in the classes of jointpoints/*.java
             to see the advice markers, etc.

*** playing with the example

    what happens if you replace !within(JoinPointTraceAspect)
                        with if(true)?

    Look at the javadocs for org.aspectj.lang.JoinPoint,
      which is the type of thisJoinPoint

    Q: How would you enforce that the amount passed to credit must be
    non-negative? 
       use before advice and throw an exception, in new aspect!
       do same using around advice 

    Q: How would you enforce this for both credit and debit?
       use a type pattern in the pointcut description

** tracing shape example

   From AspectJ Programmer's guide chapter 3, tracing section

   Show the TwoDShape and its subclasses

   To compile without aspects, use

       cd examples
       ajc -argfile tracing/notrace.lst
       java tracing.ExampleMain

*** simple

    See version1/Trace.java

    then version1/TraceMyClasses.java is an aspect that puts in calls

    ajc -argfile tracing/tracev1.lst

*** reusable

    See version2/Trace.java

    version2/TraceMyClasses.java is a concrete aspect that extends this

    ajc -argfile tracing/tracev2.lst

** subject/observer example

   cd examples/observer

   "The demo consists of the following:
     A colored label is a renderable object that has
       - a color that cycles through a set of colors, and
       - a number that records the number of cycles it has been through.
    A button is an action item that records when it is clicked."

   "With these two kinds of objects,
    we can build up a Subject/Observer relationship in which
    
      colored labels observe the clicks of buttons;

    that is, where colored labels are the observers
               and buttons are the subjects."

    see the Subject and Observer interfaces

    look at the SubjectObserverProtocol.java class

    Instantiation is in the classes

      - Button (subjects)
      - ColorLabel (observers)
      - and the aspect SubjectObserverProtocolImpl (glue)

   ajc -argfile observer/files.lst
   java observer.Demo

** others

   See also Laddad's chapter 8 for some neat examples