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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: What do you think of my CropImage class
Date: Thu, 21 Jul 2016 18:07:36 +0200
Organization: Decebal Computing
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On Thursday 21 Jul 2016 15:35 CEST, Eric Sosman wrote:

> On 7/21/2016 5:58 AM, Cecil Westerhof wrote:
>> I was not completely clear :'-( so here some more info.
>>
>> I have no real experience with Swing and had an itch to scratch.
>> That is why I wrote this program: to get some experience with
>> Swing and get a little tool to make my live a little easier.
>> [...]
>
> I have not studied your code closely, but one thing jumps out:
> You're doing Swingthings on the wrong thread.  Almost all of Swing
> is thread-unsafe, and almost all manipulation of Swing objects
> must occur on the Event Dispatching Thread, or EDT.  Your code
> breaches this requirement:
>
> - It constructs a pair of JLabels on whatever thread loads and
> initializes the class.  (And the JLabels are static, which is so
> very odd as to be downright weird.  Have you thought this through?)

Not really no: I just wanted to know if I could solve the problem of
cropping. ;-)

But about the things being static. There is always exactly one, so
what is the problem with things being static? If it is a real no-no I
could change it.


> - It constructs a bunch of Swing components on whatever thread
> executes main(). Furthermore, it manipulates those components
> (setting bounds, etc.), and even makes the JFrame visible -- all
> while running on the same wrong thread.
>
> Don't Do That.  See
>
> http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html

I will look into it. I wanted to learn, now I have to. :-D


> ... for a discussion of the issues, and how to deal with them.  (I
> rather suspect that the "flicker" you report may have its origins
> in, er, wrong-threadedness.)

No, it was that I used a Panel instead of a JPanel. I copied that part
from somewhere of the internet. I found it a little bit strange that a
Panel was used instead of a JPanel, but I thought “What do I know”? I
changed it to JPanel and that problem went away. I had to add:
    super.paintComponent(g);
to the paint function (otherwise the old one stays ‘below’ the new one
and that is a problem when the new picture is smaller as the old one),
but that is a small price to pay. :-D

Next time I should listen to that little voice.


> A few other random remarks:
>
> - You mention that "for me pack did not work," which is sort of
> weird.  I don't know what you tried before you settled on absolute
> positioning, but I wonder: Could your layout troubles have anything
> to do with the fact that CropImage extends Panel instead of JPanel?

I am going to try this out.


> - Maybe not, but then: What is the purpose of the DispImage class?
> What does it accomplish that couldn't just as well be done in the
> containing CropImage class (if the latter were a JPanel)?

I created the DispImage class to display the cropped image. And I am
going to use it to save it also. It is better to verify it before
saving it.


> - There's a handy MouseAdapter class that can eliminate some
> verbosity in your MouseListener implementation.

And something else I have to look into. I am happy to do, because I
found it much to verbose, but I did not know a better way.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof