Prev: Java and awk (jawk)
Next: Array of ArrayLists problem
From: jc_usernet on 6 Jul 2010 09:23
Hello.
I'm back into JAVA again and am curious to know the response from the
clever JAVA community about
my wish for an "easy diagnostic outputting from multiple threads to
the one text frame".

My current solution that I would like to improve on is:
-------------------------------------------------------
// DiagnosticOutput.java
// Class DiagnosticOutput updates JTextArea with output
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class DiagnosticOutput extends JFrame {
private JTextArea outputArea;
// the constructor
public DiagnosticOutput ( )
{
super( "Demonstrating Product & Consumer Thread" );

outputArea = new JTextArea( 20, 30 );
outputArea.setFont( new Font( "Monospaced", Font.PLAIN, 12 ) );
this.getContentPane().add( new JScrollPane( outputArea ) );

// set some properties of the "this" object
this.setSize( 555, 500 );
this.setVisible( true );

this.setDefaultCloseOperation ( JFrame.EXIT_ON_CLOSE );
}

// this is the method for the writing the data to the JFrame
public void put( String messageToAppend )
{
// invokeLater i understand is the thread safe way of running
the
// run method of the runnable object that is passed as a
parameter.
// Note that the runnable object also has the JTextArea object
and the
// message to append as parameters to it's constructor.
SwingUtilities.invokeLater( new RunnableOutput( outputArea,
messageToAppend ) );
}
} // end class
-------------------------------------------------------
This seems to do what I want for now. However it find this wanting
since I always have to create
an object and pass the reference around to all the participating
objects.

Is it possible to have a class without the need to explicitly create a
object for the output I want?
I am thinking along the lines of a static method like
DiagnosticOutput.put( String stringToAppend )
and first time usage creates the object and subsequent usage appends
to this hidden (from the application)
object. So all I need do is simply invoke this method at the various
location within the application.

Regards JC....
From: Lew on 6 Jul 2010 10:07
Your code seems good but you neglect to call 'pack()'. Also your
example is incomplete, but I'll assume the omitted parts are not
important.

jc_usernet wrote:
> I'm back into JAVA again and am curious to know the response from the
>

It's spelled "Java".

> My current solution that I would like to improve on is:
> -------------------------------------------------------
> // DiagnosticOutput.java
> // Class DiagnosticOutput updates JTextArea with output
>

These comments should have been in a Javadoc comment.

[snip]
> This seems to do what I want for now.  However it find this wanting
> since I always have to create an object
> and pass the reference around to all the participating objects.
>

Why is this a problem?

> Is it possible to have a class without the need to explicitly create a
> object for the output I want?

Anything's possible.

> I am thinking along the lines of a static method like
> DiagnosticOutput.put( String stringToAppend )
>

Static methods are particularly dangerous in a multi-threaded context
such as the one you need this for.

> and first time usage creates the object and subsequent usage appends
>

Lazy initialization is fraught with peril and usually provides no
benefit.

> to this hidden (from the application)
> object.  So all I need do is simply invoke this method at the various
> location within the application.
>

No, that's not all you need do. You also will need to add a bunch of
careful synchronization and spend a lot of time debugging the result
when it turns out that the use of static methods, a static object,
lazy initialization and multiple threads causes either or both of
wrong results or a huge performance bottleneck.

--
Lew
From: Lew on 6 Jul 2010 12:26
markspace wrote:
> Here's an example.  This class is, I believe, thread-safe,
> although quite simple.
>
> class TextAreaHandler extends Handler {
>
>     private final JTextArea view;
>
>     public TextAreaHandler( JTextArea view )
>     {
>        this.view = view;
>     }
>
>     @Override
>     public void publish( LogRecord record )
>     {
>        view.append( record.getMessage() );
>        view.append( '\n' );
>     }
>
>     @Override
>     public void flush()
>     {
>        // no-op
>     }
>
>     @Override
>     public void close()
>     {
>        // possibly dispose the top-level window here
>     }
>
>
>
> }
>

I worried about the 'view.append()' actions seeming not to be on the
EDT until I looked at the Javadocs for 'JTextArea#append()':
"This method is thread safe, although most Swing methods are not.
Please see _Threads and Swing_ for more information."

--
Lew
From: John B. Matthews on 6 Jul 2010 15:13
In article
<2c3b6ed9-fab7-4759-ad47-2ef5f1ee6a77(a)u26g2000yqu.googlegroups.com>,
Lew <lew(a)lewscanon.com> wrote:

> markspace wrote:
> > Here's an example.  This class is, I believe, thread-safe,
> > although quite simple.
> >
> > class TextAreaHandler extends Handler {
> >
> >     private final JTextArea view;
> >
> >     public TextAreaHandler( JTextArea view )
> >     {
> >        this.view = view;
> >     }
> >
> >     @Override
> >     public void publish( LogRecord record )
> >     {
> >        view.append( record.getMessage() );
> >        view.append( '\n' );
> >     }
> >
> >     @Override
> >     public void flush()
> >     {
> >        // no-op
> >     }
> >
> >     @Override
> >     public void close()
> >     {
> >        // possibly dispose the top-level window here
> >     }
> > }
> >
>
> I worried about the 'view.append()' actions seeming not to be on the
> EDT until I looked at the Javadocs for 'JTextArea#append()': "This
> method is thread safe, although most Swing methods are not. Please
> see _Threads and Swing_ for more information."

As a convenience when invoking append() form another thread, the
DefaultCaret update policy may be set to ALWAYS_UPDATE in order to
cause the text area to scroll automatically.

<http://java.sun.com/javase/6/docs/api/javax/swing/text/DefaultCaret.html>

This article elaborates:

<http://tips4java.wordpress.com/2008/10/22/text-area-scrolling/>

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>
 | 
Pages: 1
Prev: Java and awk (jawk)
Next: Array of ArrayLists problem