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Re: [aspectj-users] simple question
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To explain more fully, in case it helps people remember...
Join point context is determined by Java, not AspectJ.
In Java, there is no reference to an object-to-be-created
at the point of a constructor call.
In Java, "this" is available in the body of a constructor.
A pointcut should match regardless of the kind of advice,
except that after returning and after throwing specify
an additional instanceof-type check on the result or the
exception thrown, since in both cases the checked reference
only exists when exiting the join point. Rather than
having target() behave inconsistently over the lifetime
of the join point, the language designers chose to
use a separate form for this kind of post-hoc dynamic
binding. This can permit implementations to cache the
result of the pointcut once for all advice affecting
the join point, rather than re-evaluating it for each
kind or instance of advice.
If there is anything in the production-aspects section
of the programming guide that says otherwise, it's a bug.
The semantics appendix of the programming guide is the
best source for understanding the language. We should
add a table listing for each join point the advice
possible and the context available, since it's easy to
believe that all context is always available.
Wes
Ron Bodkin wrote:
David,
It's important to note that the target of a constructor call is always null, even after the join point has executed. That's what I was saying parenthetically.
I find this to be inconsistent because the value for "this" on a constructor execution join point is non-null, after the join point has returned. But it's the language design, and is not considered a bug.
Ron
Ron Bodkin
Chief Technology Officer
New Aspects of Security
m: (415) 509-2895
------------Original Message-------------
From: "Costakos,David" <costakod@xxxxxxxx>
To: "'aspectj-users@xxxxxxxxxxx'" <aspectj-users@xxxxxxxxxxx>
Date: Tue, Sep-30-2003 6:10 AM
Subject: RE: [aspectj-users] simple question
I agree that after returning advice should work. I tested your code and it
works for me.
I think the discrepancy may be centered around "target" pointcuts.
I've modified your example slightly in a way that breaks it using a target
pointcut to capture the join point context. Your example captured the
JComponent object just using after returning advice. As I read the
Production Aspects section of the online documentation, this code should
work. Have I read it wrong or misunderstood something?
import javax.swing.JTextField;
import javax.swing.JComponent;
public aspect AddToolTip {
pointcut newJ(JComponent c):
call(JComponent+.new(..)) && target(c); // <-- This uses target to
capture context
after(JComponent c) returning : newJ(c) {
c.setToolTipText("OK");
System.out.println("set tool tip");
}
public static void main(String args[]) {
JTextField comp = new JTextField();
System.out.println("text is "+comp.getToolTipText());
}
}
Thanks in advance Ron (or whoever answers this post).
-----Original Message-----
From: Ron Bodkin [mailto:rbodkin@xxxxxxxxxxxxxx]
Sent: Monday, September 29, 2003 7:38 PM
To: aspectj-users@xxxxxxxxxxx
Subject: RE: [aspectj-users] simple question
David,
After returning advice should work, if you bind the result using after
returning (JComponent c), rather than trying to use target (which is always
null for a ctor).
Another possible problem could be if you had some other advice interacting
with this one, though that seems less likely.
If, in fact, the after returning approach didn't work, it would be a bug and
it would be helpful to post a standalone example that illustrates it.
Here's an example where after returning does work:
import javax.swing.JTextField;
public aspect AddToolTip {
pointcut newJ():
call(javax.swing.JComponent+.new(..));
after() returning (javax.swing.JComponent c) : newJ() {
c.setToolTipText("OK");
System.out.println("set tool tip");
}
public static void main(String args[]) {
JTextField comp = new JTextField();
System.out.println("text is "+comp.getToolTipText());
}
}
Ron Bodkin
Chief Technology Officer
New Aspects of Security
m: (415) 509-2895
------------Original Message-------------
From: "Costakos,David" <costakod@xxxxxxxx>
To: "'aspectj-users@xxxxxxxxxxx'" <aspectj-users@xxxxxxxxxxx>
Date: Mon, Sep-29-2003 12:45 PM
Subject: RE: [aspectj-users] simple question
Having tried this out, I wasn't about to make this happen with before or
after or after returning advice.
Around advice seemed to work though:
pointcut newJ():
call(JComponent+.new(..));
Object around(): newJ() {
Object o = proceed();
((JComponent)o).setToolTipText("My Tip");
System.err.println("Set");
return o;
}
If anyone could explain why only around advice seemed to work, I'd
appreciate it!
Thanks,
Dave.
-----Original Message-----
From: Ron Bodkin [mailto:rbodkin@xxxxxxxxxxxxxx]
Sent: Monday, September 29, 2003 1:16 PM
To: aspectj-users@xxxxxxxxxxx
Subject: Re: [aspectj-users] simple question
Hi Dmitry,
You surely don't want before advice here; the given object hasn't been
initialized at that point (and target is null). For a more complete
discussion of the topic of construction join points and how to access
newly
constructed objects, see the FAQ entries 10.6 and 10.7 at
http://dev.eclipse.org/viewcvs/indextech.cgi/~checkout~/aspectj-home/doc/faq
.html#q:initializationjoinpoints
Here's a stab at how you might write your aspect. If you need to set the
tool tip "during" construction and not after, you probably will want to
write a pointcut based on being withincode of your constructors.
public aspect AddToolTip {
pointcut newJ():
call(javax.swing.JComponent+.new(..));
after() returning (javax.swing.JComponent c) : newJ(){
c.setToolTipText("OK");
}
}
Ron Bodkin
Chief Technology Officer
New Aspects of Security
m: (415) 509-2895
------------Original Message-------------
From: =?koi8-r?Q?=22=E4=CD=C9=D4=D2=C9=CA=22=20?= <dmrzh@xxxxxxx>
To: aspectj-users@xxxxxxxxxxx
Date: Sun, Sep-28-2003 11:50 PM
Subject: [aspectj-users] simple question
I want write aspect for set ToolTip text for all comonents, but this
picks
out no join points.
Help me please.
import javax.swing.JComponent;
public aspect AddToolTip {
pointcut newJ(javax.swing.JComponent c):
call(javax.swing.JComponent+.new(..))&& target(c);
before(javax.swing.JComponent c) : newJ(c){
c.setToolTipText("OK");
}
}
import javax.swing.*;
import java.awt.*;
public class MyFrame extends JFrame{
public static void main(String[] args){
MyFrame f=new MyFrame();
f.setSize(300,300);
JPanel cp=new JPanel(new FlowLayout());
JButton b=new JButton("Ok");
cp.add(b);
f.setContentPane(cp);
f.show();
}
}
Dmitriy.
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