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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> |
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<html> <head> |
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<title>AspectJ Tutorial Exercises</title> |
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<title>AspectJ Exercises</title> |
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</head> |
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<body bgcolor="white"> |
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<h1>AspectJ Tutorial Exercises</h1> |
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<h1>AspectJ Exercises</h1> |
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<h3>Organization</h3> |
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<p> The exercises work with a figure editor together with JUnit test |
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cases. They progress, as most users do in their adoption of AspectJ, |
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from non-functional, development-only aspects to aspects which augment |
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a deployed program with crosscutting features. </p> |
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<p> Before the tutorial we will make available a package that includes |
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the tests, the base code, JUnit, and a distribution of AspectJ. All |
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it needs is information about where Java lives (so set your JAVA_HOME |
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environment variable). It assumes that you unzip it in c:\ (on |
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Windows) or in your home directory (on Linux): If you put it somewhere |
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else, edit setpaths or setpaths.bat, as appropriate. Once all this is |
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done, run <code>setpaths.bat</code> or <code>source setpaths</code> to |
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export some other needed environment variables. </p> |
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<p> This tutorial consists of the attendees solving AspectJ |
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programming tasks (with unit tests) in pairs or triples and discussing |
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the answers with the group and with the tutorial presenters. The |
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exercises work with a figure editor together with JUnit test cases. |
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They progress, as most users do in their adoption of AspectJ, from |
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non-functional, development-only aspects to aspects which augment a |
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deployed program with crosscutting features. </p> |
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<p> These notes consist of four sections of exercises, a quick |
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reference to AspectJ syntax, and a UML diagram of a figure editor |
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program. While you should feel free to have a quick look through |
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these notes before the tutorial, please do not try to seriously read |
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or do the exercises; you'll learn a lot more by working through it in |
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groups. </p> |
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<h3>Command-line usage</h3> |
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<p> At the beginning of the tutorial we will make available a binary |
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package that includes the tests, the base code, JUnit, and a |
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distribution of AspectJ. All it needs is information about where Java |
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lives (so set your JAVA_HOME environment variable). It assumes that |
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you unzip it in c:\ (on Windows) or in your home directory (on Linux): |
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If you put it somewhere else, edit setpaths or setpaths.bat, as |
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appropriate. Once all this is done, run <code>setpaths.bat</code> or |
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<code>source setpaths</code> to export some other needed environment |
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variables. </p> |
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<p> All the files in the program are listed in base.lst, including |
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test cases and an empty answer aspect, |
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@@ -29,7 +42,7 @@ answers there, all you need to do is compile base.lst, either in an |
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IDE or with </p> |
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<blockquote><PRE> |
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$ ajc -Xlint -argfile base.lst |
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$ ajc -argfile base.lst |
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</PRE></blockquote> |
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<p> Before you move onto another exercise, though, make sure to copy |
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@@ -39,18 +52,11 @@ together: |
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<blockquote><PRE> |
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> copy answers/Answer.java answers/2a.java (Windows) |
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$ cp answers/Answer.java answers/2a.java (Linux) |
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$ cp answers/Answer.java answers/2a.java (Unix) |
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</PRE></blockquote> |
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<p> If you want to put your answer in a different file, say, |
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<code>answers/Answer2a.java</code>, you can compile with </p> |
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<blockquote><PRE> |
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$ ajc -Xlint -argfile base.lst answers/Answer2a.java |
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</PRE> </blockquote> |
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<p> In any case, after building the system, you should invoke Java on |
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the compiled test class. On the command-line, this this would be </p> |
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<p> After building the system, you should invoke Java on the compiled |
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test class. On the command-line, this this would be </p> |
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<blockquote><PRE> |
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$ java tests.Test2a |
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@@ -66,7 +72,7 @@ rudimentary tests on figure elements, and so is a useful test to run |
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periodically. Looking at the JUnit tests for each exercise may also |
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be helpful. </p> |
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<p> Again, ae will be looking at some solutions and having discussion, |
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<p> Again, we will be looking at some solutions and having discussion, |
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which is much more difficult without incremental solutions. So when |
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you go from one exercise to the next, make sure to save your work in a |
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file and go on to work in a different file, even if you plan to |
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@@ -91,13 +97,15 @@ shell, though, to run the JUnit tests (and don't forget to run the |
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set up the run button to run a test through the Options menu, but |
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we've found this is fairly cumbersome. </p> |
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<hr> |
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<!-- ============================== --> |
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<br style="page-break-after: always" /> |
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<h2>1. Static Invariants</h2> |
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<p> The easiest way to get started with AspectJ is to use it to |
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enforce static invariants. |
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</p> |
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<h3>a. Catch old tracing</h3> |
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<p> <strong>Sample Exercise</strong>: The main point of this exercise |
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@@ -114,7 +122,7 @@ test. </p> |
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to use <code>System.out.println()</code>, so that is what we typically |
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use for one-off debugging traces. It's a common mistake to leave |
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these in your system longer than is necessary. Type in the aspect |
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below to forces an error at compile time if this mistake is made. |
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below to force an error at compile time if this mistake is made. |
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</p> |
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<p> When you use this on the given system, you'll find one incorrect |
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@@ -163,6 +171,7 @@ aspect Answer1a { |
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of the <code>out</code> field is illegal. This will also catch those |
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users who bind System.out to a static field to save typing. </p> |
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<br style="page-break-after: always" /> |
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<h3>b. Mandate setters</h3> |
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@@ -191,9 +200,8 @@ outside of setter methods. "Outside", here, means that the code for |
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the assignment is outside the <em>text</em> of the setter. |
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<p> Make sure your program still passes the JUnit test |
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<code>tests.Test</code> before continuing, and that you see all of the |
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following warning messages. Make sure you get 11 warnings from this. |
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Wait to fix them until the next exercise. </p> |
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<code>tests.Test</code> before continuing. Make sure you get 11 |
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warnings from this. Wait to fix them until the next exercise. </p> |
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<h3>c. Refine setters mandate</h3> |
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@@ -205,9 +213,9 @@ Wait to fix them until the next exercise. </p> |
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<p> Look at some of the warnings from the previous exercise. Notice |
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that a lot of them are from within constructors. Actually, the common |
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coding convention is that no private field should be set outside of |
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setter methods <em>or constructors</em>. Modify your answer (in a new |
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file) to signal an actual error at compile time (rather than just a |
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warning) when such an illegal assignment expression exists. </p> |
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setter methods <em>or constructors</em>. Modify your answer to signal |
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an actual error at compile time (rather than just a warning) when such |
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an illegal assignment expression exists. </p> |
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<p>You'll want to add another <code>withincode</code> primitive |
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pointcut to deal with the constructors. |
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@@ -217,33 +225,38 @@ pointcut to deal with the constructors. |
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the convention is violated twice in the figures package. You should see |
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the following two errors:</p> |
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<pre> |
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.\figures\Point.java:28:9: bad field set |
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_x += dx; |
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^ |
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.\figures\Point.java:29:9: bad field set |
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_y += dy; |
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^ |
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<PRE> |
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.\figures\Point.java:37 bad field set |
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.\figures\Point.java:38 bad field set |
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2 errors |
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</pre> |
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</PRE> |
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<p>Rewrite these two occurrences so as not to violate |
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the convention. Make sure your program still passes the JUnit test |
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<code>tests.Test</code> before continuing. </p> |
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<h3>d. Congratulatoins</h3> |
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<h3>d. Congratulations</h3> |
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<p> You've taken your first steps. At this point, check the people to |
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your left and right. If they're stuck somewhere, see if you can help |
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them. </p> |
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<hr /> |
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<!-- ============================== --> |
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<br style="page-break-after: always" /> |
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<h2>2. Dynamic invariants</h2> |
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<p> The next step in AspectJ adoption is often to augment a test suite |
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by including additional dynamic tests. |
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</p> |
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<p> Tutorial attendees typically progress at different speeds through |
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these questions. Throughout this tutorial, if you finish early, see |
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what the people around you are doing and if they need help. Feel free |
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to help them out of naked self-interest; we promise you'll learn a lot |
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about AspectJ by explaining it. </p> |
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<h3>a. Check a simple precondition</h3> |
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<p> <strong>Sample Exercise</strong>: We've provided the answer to |
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@@ -280,7 +293,7 @@ Tests run: 7, Failures: 2, Errors: 0 |
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</p> |
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<blockquote><PRE> |
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$ ajc -Xlint -argfile base.lst answers/Answer.java |
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$ ajc -argfile base.lst answers/Answer.java |
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$ java tests.Test2a |
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....... |
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@@ -310,6 +323,9 @@ aspect Answer2a { |
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<p> <strong>Task:</strong> Pass <code>tests.Test2b</code>. </p> |
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<p> <strong>Tools: </strong> <code>call</code>. |
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</p> |
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<p> <code>Group</code> is a <code>FigureElement</code> class that |
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encapsulates groups of other figure elements. As such, only actual |
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figure element objects should be added to <code>Group</code> objects. |
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@@ -340,19 +356,32 @@ call. |
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<h3>d. Assure input</h3> |
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<p> <strong>Task: </strong> Pass <code>tests.Test2g</code>. |
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<p> <strong>Task: </strong> Pass <code>tests.Test2d</code>. |
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</p> |
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<p> <strong>Tools: </strong> around advice |
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</p> |
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<p> Instead of throwing an exception when one of <code>Point</code>'s |
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<code>int</code> fields are set to an out-of-bounds value, write an |
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aspect to trim the value into an in-bounds one. You'll want to use |
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<code>around</code> advice that exposes the new value of the field |
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assignment with an <code>args</code> pointcut, and |
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<code>proceed</code> with the trimmed value. </p> |
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<code>int</code> fields are set to a negative value, write an aspect |
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to trim the value to zero. You'll want to use <code>around</code> |
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advice that exposes the new value of the field assignment with an |
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<code>args</code> pointcut, and <code>proceed</code> with the trimmed |
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value. </p> |
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<p> This is going to look something like |
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</p> |
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<pre> |
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aspect A { |
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void around(int val): <var><Pointcut></var> { |
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<var><Do something with val></var> |
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proceed(val); |
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} |
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} |
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</pre> |
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<br style="page-break-after: always" /> |
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<h3>e. Check a postcondition</h3> |
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<p> <strong>Task: </strong> Pass <code>tests.Test2e</code> |
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@@ -363,7 +392,7 @@ assignment with an <code>args</code> pointcut, and |
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<p> A postcondition of a <code>Point</code>'s <code>move</code> |
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operation is that the <code>Point</code>'s coordinates should change. |
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If a call to move move didn't actually move a point by the desired |
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If a call to move didn't actually move a point by the desired |
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offset, then the point is in an illegal state and so an |
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<code>IllegalStateException</code> should be thrown. |
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</p> |
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@@ -389,22 +418,14 @@ element's bounds rectangle should move by the same amount as the |
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figure itself. Write an aspect to check for this postcondition -- |
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throw an <code>IllegalStateException</code> if it is violated. </p> |
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<h3>Help Yourself by Helping Others</h3> |
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<p> At this point, check the people to your left and right. If |
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they're stuck somewhere, see if you can help them. </p> |
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<hr /> |
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<!-- ============================== --> |
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<br style="page-break-after: always" /> |
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<h2>3. Tracing</h2> |
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<p> The crosscutting feature you will be adding in part (4) will be |
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support for caching the bound objects of <code>Group</code> figure |
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elements, which may be costly to compute. On the way to that, though, |
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it's useful to explore the system with some tracing aspects. </p> |
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<p> Tracing is one of the classic AspectJ applications, and is often |
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the first where AspectJ is used on deployed code. |
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</p> |
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<h3>a. Simple logging</h3> |
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@@ -420,7 +441,7 @@ in the figures package. To do this, use the utility class |
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<code>Log</code> (with an import from <code>support.Log</code>) |
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and call <code>Log.log(String)</code></p> |
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<h3>b. Simple logging</h3> |
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<h3>b. Exposing a value</h3> |
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<p> <strong>Task:</strong> Pass <code>tests.Test3b</code>.</p> |
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@@ -441,35 +462,16 @@ but also the target object, with the form |
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<p> <strong>Task:</strong> Pass <code>tests.Test3c</code>.</p> |
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<p> <strong>Tools:</strong> |
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<p> <strong>Tools:</strong> <code>args</code>. |
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</p> |
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<p> Write an aspect to log whenever a <code>Point</code> is added to |
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a group (including initially). To do this, use the utility class |
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<code>Log</code> (with an import from <code>support.Log</code>) and |
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call </p> |
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<blockquote><PRE> |
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Log.log("adding Point") |
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</PRE></blockquote> |
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<p> This will write the string "adding Point", followed by a semicolon |
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terminator, to the Log. For example, with your aspect enabled, </p> |
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<blockquote><PRE> |
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Point p1 = new Point(10, 100); |
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Point p2 = new Point(10, 100); |
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Group g = new Group(p1); |
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g.add(p2); |
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System.out.println(Log.getString()); |
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</PRE></blockquote> |
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<p> Write an aspect to log whenever a <code>Point</code> is added to a |
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group. The <code>args</code> pointcut allows you to select join points |
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based on the type of a parameter to a method call. </p> |
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<p> should print out "adding Point;adding Point;". |
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<p> Look at the test case for details about the tested log message. |
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</p> |
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<p> <em>Hint: The <code>args</code> pointcut allows you to select join points |
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based on the type of a parameter to a method call. </em> </p> |
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<h3>d. Logging extended to checking an invariant</h3> |
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<p> <strong>Task:</strong> Pass <code>tests.Test3d</code>.</p> |
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@@ -477,8 +479,18 @@ based on the type of a parameter to a method call. </em> </p> |
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<p> <strong>Tools:</strong> <code>inter-type field declaration</code> |
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</p> |
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<p>Make sure that a Point is never added to more than one Group.</p> |
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<p> Make sure that a Point is never added to more than one Group. |
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To do so, associate a boolean flag with each Point using an inter-type |
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declaration, such as </p> |
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<blockquote><pre> |
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boolean Point.hasBeenAdded = false; |
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</pre></blockquote> |
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<p> Check and set this flag with the same kind of advice from your |
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answer to problem (c). Throw an <code>IllegalStateException</code> if |
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the point has already been added. |
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</p> |
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<h3>e. Better error messages for 3d</h3> |
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@@ -487,53 +499,9 @@ based on the type of a parameter to a method call. </em> </p> |
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<p> <strong>Tools:</strong> |
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</p> |
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<p>Make sure that a Point is never added to more than one Group. |
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Include the Group that the Point was previously a part of in the |
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thrown exception.</p> |
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<h3>c. Keeping track of state</h3> |
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<p> In this exercise, perform the tracing from part (a), but also log |
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the enclosing group, if any, of the moving point. You can use an |
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inter-type declaration inside your aspect to associate a |
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<code>Group</code> field with <code>Point</code> objects, and then |
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work with that field, setting it appropriately when the |
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<code>Point</code> is added to a <code>Group</code> (at the same join |
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points you were tracing in part b). So </p> |
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<blockquote><PRE> |
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Point p1 = new Point(10, 100); |
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p1.move(0, 0); |
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System.out.println(Log.getString()); |
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</PRE></blockquote> |
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<p> should print out "moving as a part of null;", but |
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</p> |
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<blockquote><PRE> |
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Point p1 = new Point(10, 100); |
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Group g = new Group(p1); |
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p1.move(0, 0); |
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System.out.println(Log.getString()); |
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</PRE></blockquote> |
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<p> should print out "moving as a part of Group(Point(10, 100));", |
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which you can do by using the toString() method already defined on |
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Group. </p> |
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<p> <em> Hint: This exercise combines the tracing from parts a and b. |
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If you start with an aspect that includes the solutions to those |
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previous exercises, you'll be most of the way there. </em> </p> |
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<p> Test this with the JUnit test case <code>tests.Test3c</code>. |
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<h3>Help Yourself by Helping Others</h3> |
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<p> At this point, check the people to your left and right. If |
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they're stuck somewhere, see if you can help them. </p> |
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<hr /> |
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<p> Extend your solution to problem (d) by using the string |
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representation of the Point's containing group as the <code>msg</code> |
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part of the <code>IllegalStateException</code>. </p> |
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<!-- ============================== --> |
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@@ -577,7 +545,7 @@ around advice intercepting the method. |
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<p> <strong>Task:</strong> Pass <code>tests.Test4b</code>. |
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</p> |
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<p> <strong>Tools:</strong> <code>private Rectangle Group.mumble;</code> |
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<p> <strong>Tools:</strong> inter-type field. |
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</p> |
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<p> Instead of making the (very) conservative approximation of |
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@@ -605,12 +573,11 @@ Change your aspect so that it invalidates the cache whenever the |
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<code>move()</code> method of <code>Group</code> is called. |
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</p> |
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<br style="page-break-after: always" /> |
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<h3>d. Invalidate, part 2</h3> |
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<p> <strong>Task:</strong> Pass <code>tests.Test4d</code>.</p> |
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<p> <strong>Tools:</strong> <code>your solution to 3c</code></p> |
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<p> Of course, part (c) didn't really solve the problem. What if a |
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<code>Point</code> that is part of a <code>Group</code> moves? |
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Whenever either of a Point's fields are set it should invalidate the |
ehilsdal
пре 21 година