2002 Palo Alto Research Center, Incorporated. All rights reserved.
</para>
<!-- todo Update me! -->
- <para>Last updated on the web November 26, 2002.
+ <para>Last updated December 31, 2002.
</para>
<para>
For a list of recently-updated FAQ entries, see <xref linkend="q:faqchanges"/>
AspectJ 1.1 is currently in development, and
some answers may change after it is released;
- for more information, see the
- <ulink url="http://aspectj.org/doc/readme11/index.html">AspectJ 1.1 README</ulink>.
- This is a web-only distribution of the FAQ; the 1.0 documentation bundle
- contains an earlier version.
+ for more information, see the README
+ included with the AspectJ 1.1 distribution.
</para>
<qandaset defaultlabel="number">
<qandadiv id="overview" xreflabel="Overview">
</para>
</question>
<answer>
+ <para>
+ Briefly, there are two interesting times when a constructor or method is
+ run. Those times are when it is called, and when it actually
+ executes.
+ </para>
+ <para>
+ The main difference is that a call join point happens outside of
+ the object (for non-static methods) or class (for static methods
+ and constructors), and that an execution join point happens inside
+ the object or class. This means that the <literal>within</literal>
+ and <literal>withincode</literal> pointcuts pick them out
+ differently: A call join point is picked out within the caller,
+ while an execution join point is picked
+ out where it is actually defined.
+ </para>
+ <para>
+ A call join point is the ``outermost'' join point for a particular
+ call. Once a call join point proceeds, then a number of different
+ things happen. For non-static methods, for example, method
+ dispatch happens, which will cause one method execution join point
+ -- perhaps more, if there are super calls. For constructors, the
+ super constructor is called, and fields are initialized, and then
+ various constructor execution join points will occur.
+ </para>
+ <para>
+ A call join point matches only the ``external'' calls of a method
+ or constructor, based on a signature, and it does not pick out
+ calls made with <literal>super</literal>, or
+ <literal>this</literal> constructor calls.
+ </para>
+ <para>Here's more detail:
+ </para>
<para>Consider method execution in Java as (1) the initial call from
this object to some method on the target object with a
particular signature; and (2) the execution of the actual code
</para>
</answer>
</qandaentry>
- <qandaentry>
- <question id="q:compareccallandexecution"
- xreflabel="Q:What is the difference between call and execution?">
- <para>
- What is the difference between call and execution?
- </para>
- </question>
- <answer>
- <para>
- There are two interesting times when a constructor or method is
- run. Those times are when it is called, and when it actually
- executes.
- </para>
- <para>
- The main difference is that a call join point happens outside of
- the object (for non-static methods) or class (for static methods
- and constructors), and that an execution join point happens inside
- the object or class. This means that the <literal>within</literal>
- and <literal>withincode</literal> pointcuts pick them out
- differently: A call join point is picked out within the caller,
- while an execution join point is picked
- out where it is actually defined.
- </para>
- <para>
- A call join point is the ``outermost'' join point for a particular
- call. Once a call join point proceeds, then a number of different
- things happen. For non-static methods, for example, method
- dispatch happens, which will cause one method execution join point
- -- perhaps more, if there are super calls. For constructors, the
- super constructor is called, and fields are initialized, and then
- various constructor execution join points will occur.
- </para>
- <para>
- A call join point matches only the ``external'' calls of a method
- or constructor, based on a signature, and it does not pick out
- calls made with <literal>super</literal>, or
- <literal>this</literal> constructor calls.
- </para>
- </answer>
- </qandaentry>
<qandaentry>
<question id="q:recursiveentrypoints"
xreflabel="Q:How do I say that I want the topmost entrypoint in a recursive call?">
</para>
</answer>
</qandaentry>
+ <qandaentry>
+ <question id="q:adviseconstructors"
+ xreflabel="Q:How do I work with an object right when it is created?">
+ <para>How do I work with an object right when it is created?
+ </para>
+ </question>
+ <answer>
+ <para>
+ You can advise some form of constructor join point.
+ Constructors are tricky in Java, and that's exposed in AspectJ.
+ Here are some rules of thumb:
+ <itemizedlist>
+ <listitem>
+ <para>If you want the join point on the "outside" of object creation,
+ use after returning from call to the constructor:
+ </para>
+ <programlisting>
+ after() returning (Foo newlyCreatedObject): call(Foo.new(..)) { ... }
+ </programlisting>
+ <para>
+ You might be tempted to use "this" or "target" to expose the new object, but remember
+ that if you're on the "outside" of object creation, the object itself might not be
+ created yet... it only exists "on the way out", when you return the object.
+ </para>
+ </listitem>
+ <listitem>
+ <para>If you want the join point inside a particular constructor, use:
+ </para>
+ <programlisting>
+ after(Foo newlyCreatedObject) returning: this(newlyCreatedObject) && execution(Foo.new(..)) { ... }
+ </programlisting>
+ <para>
+ Remember, though, that if you use "before" advice here, the body of the constructor
+ will not have run, and so the object may be somewhat uninitialized.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ In the rare case that there are all sorts of constructors for the object that call
+ each other with <literal>this(...)</literal> and you want exactly one join point
+ for each initialization of <literal>Foo</literal>, regardless of the path of
+ constructors it takes, then use:
+ </para>
+ <programlisting>
+ after(Foo f) returning: this(f) && initialization(Foo.new(..)) { ... }
+ </programlisting>
+ </listitem>
+ </itemizedlist>
+ </para>
+ </answer>
+ </qandaentry>
<qandaentry>
<question id="q:andingpointcuts"
xreflabel="Q:I want advice to run at two pointcuts, but it doesn't run at all.">
</question>
<answer>
<para>
- Entries changed since the earlier September 13 version:
+ Entries changed since the earlier November 26 version:
<itemizedlist>
- <listitem><para><xref linkend="q:ajdocneeds13"/></para></listitem>
- <listitem><para><xref linkend="q:idebugs"/></para></listitem>
- <listitem><para><xref linkend="q:ajcbugs"/></para></listitem>
- <listitem><para><xref linkend="q:searchingsite"/></para></listitem>
- <listitem><para><xref linkend="q:bytecodeweaving"/></para></listitem>
- <listitem><para><xref linkend="q:differences"/></para></listitem>
- <listitem><para><xref linkend="q:schedule"/></para></listitem>
- <listitem><para><xref linkend="q:aopinjava"/></para></listitem>
- <listitem><para><xref linkend="q:aspectjandj2ee"/></para></listitem>
- <listitem><para><xref linkend="q:applets"/></para></listitem>
- <listitem><para><xref linkend="q:packagedeclares"/></para></listitem>
- <listitem><para><xref linkend="q:writingbugsandemails"/></para></listitem>
- <listitem><para><xref linkend="q:andingpointcuts"/></para></listitem>
- <listitem><para><xref linkend="q:idesupportplans"/></para></listitem>
- <listitem><para><xref linkend="q:opensource"/></para></listitem>
+ <listitem><para><xref linkend="q:adviseconstructors"/></para></listitem>
</itemizedlist>
</para>
</answer>
projects / aspectj.git / commitdiff