Develop Reference

How can I make it so Eclipse automatically updates my code in a window as I edit it?

How can I make it so Eclipse automatically updates my code in a window as I edit it? I've seen the feature before in youtube videos but I cannot find it. For example : I change a JApplet rectangle width from 20 to 10, I want to see it update immediately.

I've seen Notch do this on development videos (Minecraft), it is awesome but I don't know exactly how he does it.
-- EDIT --
This has been bugging me so I went and googled "how does notch code" and found this on a blog page https://gun.io/blog/what-i-learned-from-watching-notch-code/. It doesn't say exactly how it was done but gives a good hint (HotSwap) and makes it seem like he set it up himself without external software. Here's the most relevant section:
Incredibly Fast Testing
He began by building the engine, and to do this he used the ‘HotSwap’ functionality of the Java JVM 1.4.2, which continuously updates the running code when it detects that a class has changed.
When building the engine, Notch wrote a function which would continuously pan the camera around and clip through the walls and keep the view on top, so he could make changes to the code and see the effects they made in real time. I’m used to testing by writing a function, building it, installing it on the device I’m testing on, and then seeing the result, which can take up to a minute at a time, so it’s easy to see how HotSwapping could save a lot of development time.
--- ORIGINAL POST CONTINUED ---
I get a similar effect by using groovysh though, works smoothly and can use all your java classes as is.
What I'll usually do is write all my code in java, then go and fire up "Groovysh" where it will give you a little window to enter commands (You may have to ensure the classpath works correctly outside of eclipse). I can then "new" any of my classes and call methods on them one line at a time. When you do myFrame.setSize([100,100]) you will see it change immediately.
A good test is to just run groovysh and type something like:
import javax.swing.*
f=new JFrame()
f.setVisible(true)
f.setSize(100,100)
or the groovier version:
f=new JFrame(visible:true, size:[100,100])
and you will see your frame resize on the screen. You can even drag it bigger and then do something like:
println f.getWidth()
to show your new width. It's fun to interact this way but it's more complicated if you want to actually change your class definition and see it pick up the change, I have no idea how Notch did that. I looked into it a little--it's possible he was using something like JRebel
It requires something special since you would have to dynamically reload the classfile into your running system on every save--something that should have serious classloader issues.
By the way there is also a way to get your Java program to throw out a little GroovyConsole which will allow you to inspect and modify all the variables in your running code (but again you can't replace definitions of existing classes).
Also see answer here:
Change a method at runtime via a hot swap mechanism

Necessary and sufficient conditions to run Java applets and JWS applications in browser?

I have already asked this and was heavily downvoted. Unfortunately, I still can't solve it. I don't know what I do, but sooner or later I loose an ability to run java applets and java web start applications in all browsers.
Here is an example what is happening.
I am opening page with applets http://csis.pace.edu/~bergin/Java/applets.htm and getting the following picture:
with signs plugins were blocked. I am trying to unblock
which causes another dialog
after OK I have another
next
if clicked
And so on.
Applet doesn't run.
After dancing with PATHes, Java updates and so one, once I can have applet run. But sooner or later I will stuck in this position again.
I would like to know, is it possible to exclude this situation in principle?
I mean I don't want to disable security at all, but I mean that in case my explicit permission everything should run. Is it possible to do that?
UPDATE
First of all, I don't understand, why can't I run applet on outdated java if I want?
I am a human and robots should obey me! :)
Suppose I wish to debug my applet on old version of java, why not?
Second, there is no information about what version it thinks I have and what version it wants?
Without this information it is possible that there is just a bug in version detection mechanism.
I have multiple versions of Java in Program Files since I am a Java developer. Then how can I know which one it uses?
UPDATE 2
I have updated my Java from 1.8.0_20 to 1.8.0_25 and now situation have changed, but applets are sill impossible to run.
The proof I have "latest" java:
The proof I have added the site above to exclusions list:
The effect of applet run:
(applet not runs)
Clicking details result:
(no any details in fact)
So, what to do?
UPDATE 3
This site is not working: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012VP113;orb=1;cov=0;log=0;cad=0#orb
(show orbit diagram)
Reloading/restarting browser does not help.

I looked at your html source and realized you're using the .class file directly instead of wrapping it in a jar file. This is what you have:
<applet code="GSort.class" width=700 height=400>
I think applets no longer work when using .class files directly due to new security requirements. They have to be wrapped in jar files because you need to add some security settings to the meta-inf folder of the jar file. Here is how oracle recommends deploying an applet:
https://docs.oracle.com/javase/tutorial/deployment/applet/deployingApplet.html
Edit:
I tried again with adding the site url to the Java security exception list and this time I got it to work! It looks like chrome stays in memory after exiting so changing Java security doesn't affect it unless you shut down chrome completely and restart it. Easiest way is to use Internet Explorer. Try it with Internet Explorer and it should work (assuming that you still have the site added under java security exception list).

Can Matlab deploytool compile files with javax.swing elements?

Suppose I have a set of codes to display a JFrame, a JPanel, and a JLabel. This works fine if I run it as a script file. It just shows a tiny window with a label that says "A label" exactly like you would expect:
frame = javax.swing.JFrame('Test');
panel = javax.swing.JPanel();
label = javax.swing.JLabel('A label');
panel.add(label);
frame.add(panel);
frame.setDefaultCloseOperation(javax.swing.JFrame.HIDE_ON_CLOSE);
frame.pack();
frame.setVisible(true);
The problem comes when I compile this as an exe file with the deploytool. It will compile and I can run the program, but the frame will show up for about 3 seconds or so then disappear. If I run from inside Matlab with !main.exe, there is no error message when the window disappears (I don't want to say it crashes because there is no error message). Neither is there one if I run the executable from the Windows command prompt (same results -- shows for a few seconds and then crashes).
Any ideas what is going on here? I can compile other files just fine. Is the problem because I included the javax.swing elements?
Many thanks for your help.
UPDATE
This feels like a really cheap hack, but having a while loop that pauses Matlab as long as the JFrame is open does the trick. So now the question is, is there a better way to do this?

The problem is probably that your main M-code function finishes executing, and since there are no figures up, Matlab decides to exit. In a Java Swing program, what would happen is that things would keep going until all the Swing windows are closed or you explicitly terminate the program. Since this is a Matlab program, the layer that's "in control" is the Matlab handle graphics layer, so you need to either have the main function executing or a figure up. (In interactive Matlab, it'll keep running as long as you have the IDE up, but there's no IDE in a compiled Matlab program, so when its work is done, it exits.)
The "Right Thing" to do from MathWorks' perspective is to probably buy the Matlab Builder JA toolbox, build the Matlab part of your program in to a Java library, include that in a main program which you write in Java. That way the Java layer is "in control" of the main execution sequence, and the "stay running as long as there are Java windows open" logic you're expecting will be in effect.
If you want to hack this to make it work in your current program structure, your invisible figure window might be a good one. Though you will need to make it Visible to have it work; invisible figures don't count for keeping a Matlab GUI running. You may be able to hide it from the user by changing its position to move it entirely off the user's screen.
Then you need to terminate the program somehow. Some part of your code is going to know when the program should end. That sounds like it's the Java part of your code. From there, you could just call java.lang.System.exit(). If you need to do Matlab-layer stuff, you could exit from M-code by communicate the "it's time to exit" back to your Matlab code, which could then call exit() or close that figure. You could do this by setting a public class variable in one of your Java classes, and have a Matlab timer object that checked that variable every 500 milliseconds or so.
If the condition that ends the program is that all your Java Swing windows get closed, that's a little tougher. Because the Matlab figure window itself is a Java AWT or Swing window, so as long as that's open you're not getting down to zero windows. What you could do is have that Matlab timer, instead of looking for a class variable, check the list of open Java windows and see if the Matlab figure is the only one left, and if so, close it or exit explicitly.

Turning java application into applet

I followed a tutorial for a bit of learning java 2d gaming. It included turning it into an applet.
I use a class which is the launcher class, and it basically just launches it. It can be run as applet (using init) or an application (with main)
I expanded upon the code greatly, Adding a save and load feature using a flat .txt and .png files. which used get_property("user.home") and so forth.
Now I know that applet's on the browser can not save/view the persons computer information. So the above is useless for an applet.
What I have tried doing is commenting and adjusting everything that includes the persons computer information and so forth, And I still can not get the applet to load.
I am using dropbox to host it, I have tried different browsers and made sure the applet was not loaded into my cache for changes I did.
The applet in my eclipse IDE works fine-even saves, so I can't trust it, so I am using dropbox.
My applet did work, this was a long time ago before I developed the engine into my game.
I will share my GameHandler class because it holds the meat of the game. I really should organize this better. Any suggestions?
http://pastebin.com/zdmexGya GameHandler class.
I'm positive saveGame and loadGame do not even get called.

restart java.exe from an applet

I have an applet packaged with a third part dll (from JTwain). My applet scans documents from the TWAIN compatible default printer. The applet fails on a paper jam and won't recover. The user navigates away from the page and the applet is destroyed. When returning to the page it fails again. Closing the browser (which kills java.exe process on the pc), and then returning to the page clears the problem and everything works.
I want to restart everything without requiring users to close down the browser. I've added a GUID query string to the URL's from which the applets resources are loaded - so I know nothing is being cached. I've checked in the windows task manager and there is no process created by the dll, it's all happening within the main java.exe process. I tried wrapping the scanning process in a thread so I could interrupt it in the stop or destroy methods (just in case the applets thread weren't stopped when the applet was destroyed), but that didn't work.
Any suggest would be greatly appreciated. Ideally I'd like some way to restart java when the applet unloads (but I doubt that's possible).
UPDATE
I've spent a couple of days trying to identify what causes the applet to fail. I still don't know :(
When the paper jam occurs something (not my code), is producing a couple of popups. The first alerts the user of the jam, and can be closed by clicking the OK button. The second says 'reading from device' and hangs. It cannot be close with the red, close window, icon in the top corner - I kill it from the task manager and windows asks to send a report regarding the 'non-responsive program'. I assume these popups are produced by the dll. And given that the second hangs, my assumption is that a thread started by the dll has hung while retaining a lock on some component of the TWAIN application. I get
com.asprise.util.jtwain.JTwainException: Failed to open the specified data source:
Source: TW-Brother MFC-9970CDW LAN Thrown
..when I try to access the scanner.
I'm at a bit of a loss as to how I can get more information. I'm testing my applet on a windows virtual pc (so as to use ie7), and don't have a method for step debugging in this environment. (And it's crashing on third party code for which I have no source anyway)

I see only two practical options here:
Use an API that handles paper jam without problems. Of course, that is easy to say (get robust API), harder to find.
Launch the app. free floating using Java Web Start. If it freezes up, the user can kill it and click the link for another instance in a new JVM. Or the applet might also call BasicService.showDocument(URLof.jnlp) if it can detect a problem with the DLL and is not itself frozen.
Of course, you should also report the bug to the ..Asprise(?) developers. The optimal solution would be to have the problem fixed at its source. Anything we do here is a 'workaround'.