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Old 03-09-2013, 08:30 AM   #11
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Default Re: Java Programming Application

Quote:
Originally Posted by drill View Post
Sure, be my guest. I always look forward to learning how to code better
In that case, here goes!

First off, I'm not sure how much experience you have with either / or Swing and threading? There's a few rules that need to be followed to guarantee that your application will be free of threading bugs, and the main one in this instance is that you must only ever do anything to Swing components if you're running on the event dispatch thread (see here for details.)

Quote:
This is necessary because most Swing object methods are not "thread safe": invoking them from multiple threads risks thread interference or memory consistency errors.
Granted, some Swing objects *are* thread safe, but for the moment assume that none are - it's considered good practice to just do everything that needs to be done in Swing on the EDT.

In your case, the update() method is called from an arbitrary thread which is most definitely *not* the EDT (it's one that you've just created), so this is especially dangerous since the two are running concurrently. (No, you might not usually run into these problems with simple applications, but for more advanced ones you definitely will at some point, so pays to have it right straight off.)

If you're not on the EDT but you want to execute a piece of Swing code on the EDT, then it's relatively easy to do:

Code:
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            //Code to run on the EDT goes here.
        }
    });
This essentially schedules a runnable to be executed on the EDT - it will be invoked at some point in the near future. If you want to wait until that drawing code is complete (which isn't usually what you want but is available anyway) then use invokeAntWait() rather than invokeLater(). As you've probably already found, if you attempt to do *everything* on the EDT then your application will just appear to lock up while these tasks are completing, not what you want.

You may be starting to realise there's more to threading than you first thought - it's a hugely complicated topic, entire books have been written on threading issues you can come across just in Java (Java concurrency in practice is a great book if you're interested, but not for the beginner.) Introducing threading to your application unlocks a whole potential hive of livelocks, deadlocks, race hazards and so on, and many will be unpredictable and hard to track down. So use threads wisely, and only when you have to

In terms of other points, overall it's not bad but I'd suggest a few style / misc changes:
  • Comments are a bit sparodic - you've put one about declaring the variables, but this isn't really needed (it's obvious to anyone reading the code that's what you're doing.) However, you should really comment all methods and explain what they do, because that isn't so obvious. In these comments you can put things like whether the method needs to be executed on the EDT or not in order to aid others that may be using your code. Might not be important now, but in a team of people or on a large codebase good commenting gets incredibly important. Use the set Javadoc style for this.
  • Your imports are a bit sparodic - you've got one star one and the rest are just individual imports. I'd advocate using individual imports for everything, since it makes it clearer to the reader what you're importing and mitigates name clashes (two classes with the same name in different packages you may be importing.) Whatever you choose, make it consistent.
  • A lot of things are static that shouldn't be static - unless you can really justify it, nothing should really be static (at least tell yourself that to start with.) I see nothing in that class that should really be static.
  • With fields such as "private static ArrayList<JLabel> labels = new ArrayList<JLabel>();" - first off you don't need the second JLabel class, you can use diamond, and secondly it's better practice to use an interface type for the field rather than tying it to an implementation - it makes things much easier to swap out that way. So it would become: "private static List<JLabel> labels = new ArrayList<>();" (where list is java.util.List.)

So overall, it's not bad - but there are definitely things you can work on even if you want to just keep the same level of functionality!
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Old 03-09-2013, 09:21 AM   #12
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Default Re: Java Programming Application

Quote:
Originally Posted by berry120 View Post
First off, I'm not sure how much experience you have with either / or Swing and threading?
As you guessed, I am very new to threading. So new that this is my first application that involves threading. And to be honest, I didnt hear of EDT until just now. I will probably fix a good bit of my code up later today when I have more time. Also, I dont remember why I had all those statics (as I wrote this a couple weeks ago and I have a very bad memory), but I remember coming across errors, and all I had to do was declare the variable a static to fix them (yes I usually go the path of least resistance).

You taught me a lot about threading today so

---------- Post added at 09:21 AM ---------- Previous post was at 09:19 AM ----------

Quote:
Originally Posted by Fujitsu_Technician View Post
as long as you are happy with your work drill that is the main thing as it is not my adopted launage I don't tend to run jarva application much well not JAR files anyway but I respect you for your work and shear your views on programming like I do any one who can program as there is so much to learn in each language Best of luck.

Kind Regards
Well thanks, and I can understand your hesitance to use java apps as that I have seen it before. If you ever change your mind about them you are welcome to use the java apps that I post.
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Old 03-09-2013, 09:24 AM   #13
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Default Re: Java Programming Application

Quote:
Originally Posted by drill View Post
As you guessed, I am very new to threading. So new that this is my first application that involves threading. And to be honest, I didnt hear of EDT until just now. I will probably fix a good bit of my code up later today when I have more time. Also, I dont remember why I had all those statics (as I wrote this a couple weeks ago and I have a very bad memory), but I remember coming across errors, and all I had to do was declare the variable a static to fix them (yes I usually go the path of least resistance).

You taught me a lot about threading today so
It was probably because you came across an error that went something like "non-static variable cannot be referenced from a static context" - in this case making everything static appears to fix the error quite quickly, but in fact breaks the OO model, since whatever you make static will no longer be tied to the object, it will be tied to the class instead (which while it seems to work in the trivial case, usually isn't what you want at all.)

And you're welcome in terms of the threading stuff, just be aware that it's not nearly as trivial as it might seem in the majority of cases. The java.util.concurrent package has some really useful classes in this regard and supports all sorts of things, but perhaps best to leave that until a bit later
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