I recently created a project in Netbeans using VirtualBox on which i installed windows XP (Not activiated)
My Windows required me to activate and would not allow me access to my files on the computer before i activate it, i stupidly went and uninstalled XP and reinstalled it, thinking i'll have access to all the files from the JAR file i created
I want to know if theres any way i can use the class files of the project i created, to create new java files so that i can edit the code in netbeans ??
Please if anyone can shed some light on this topic, if its at all posible to gain access to the forms java content i created. Im new to programming and this is something above my knowledge (i hope this makes sense)
If not possible please let me know what an absolute idiot i am, so that i can start re creating the project from scratch ... Sigh, and thank you
A jar/class file is compiled bytecode that is not human-readable... but with Java it is easily converted back. Look into a program like JavaDecompiler.1 This is not my program but I use it and I find it workable for my needs.
1 If this is considered spam I'll gladly invalidate the link.
As a sidenote: You are lucky that its Java. In many other languages like C++ that would hardly be possible. The difference is that Java does not compile the source code to machine code. That step is hardly reversible since for example all variable names are lost. Try to understand a non-trivial piece of code without helpful variable names...
Java instead compiles the source code to byte code which then is interpreted by Java on runtime. That byte cold holds way more information about the original source code than machine code.
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How is the java utility that begins the process of launching a class told to "spill its guts" on what it's doing as it tries to load classes?
In particular, what file paths is it TRYING to access, only to perhaps discover whatever it's looking for is not there, at least as it interprets the specification given? There was a way to get that information, but I can't find it now.
Note that this is Java version "1.8.0_333" on Windows 10.
I've tried every flag known to me, via the -h and -X flags, and I strongly suspect what I'm looking for is (was) an X flag that's been removed, just as the -X help output warns. And so, there must be an OS way to figure this out, I sure hope!
You might ask why? Whatever for? What are you trying to do? Well, that's the bulk of this question's text. To wit:
As one of the very early users of Java (I started with 1.1) way back in the '90s, I had an issue moving an application suite I'd written for my company on Linux to MS Windows and I got it working by using Cygwin. Along the way, this same sort of issue came up and I quite vividly recall having found a mechanism for getting the Java launcher to articulate just what file specifications - paths - it was actually using in searching for the appropriate class. And through using this, I found that the CLASSPATH was being specified incorrectly, and with some experimentation, I got it working reliably. Now I need to do that again!
This flag I'd used was immensely helpful in figuring out just what the file specification format CLASSPATH needed to be (we're not talking semicolons here) this combination of OS, Java, and Cygwin. After some hours of what I hope was reasonable hunting, I'm wondering if this capability has been removed at some point? Either that or "I'm looking for the wrong thing." Heck, since the source is available (I think!), maybe some brave soul has hacked the java utility to do such a thing?
It may help to understand that for this application I wrote for my company, it was a major goal to have the source work pretty much the same on all Windows and Linux / Unix systems (and at the time, macOS), and just use a configuration file to tell the code what's different. And that wasn't easy to figure out, but with this flag, it wasn't that hard, either.
But, unfortunately, I haven't needed this knowledge since I figured it all out all those years ago, and apparently, this little kernel of knowledge is very hard to find today. Or, it's no longer pertinent to the modern version(s).
I don't think this has anything much to do with the actual problem, but it may help in people's thinking if they understood the scenario: The current situation is that I have a fully functional installation of this software on Windows 7 to use as a comparison for how to configure things on Windows 10 (and hopefully younger). The Windows 7 is running a pretty modern Cygwin installation and very nearly the most modern Java - just a sub-version away from the new installation from last week on a Windows 10 box. (Everything's bright and shiny new on the new box.)
The required format for CLASSPATH on the nearly identical but fully functional Windows 7 system is:
CLASSPATH="C:/opt/OurInstallationDir/lib"
And that's it.
This value is picked up in several places as the code later needs to launch Java itself to do some unusual things. However, the java command that gets it all going is launched from a C program - not that that matters for this problem - but the C program (compiled under Cygwin, but perfectly runnable from any Windows environment) helps ensure that the Java environment is secured (policy file contents and so forth) before getting into Java, else it refuses. And this program on Windows 11 launches Java just fine, it's just giving it a CLASSPATH that isn't useful, apparently, even though the files are there where they should be, etc.
Configuring things as before just doesn't work, even from the command line. No version of specifying CLASSPATH seems to work if it's more than a dot; the only thing that works, is being in the /lib directory when starting and using "-cp ." ... But that's just not going to fly for so many reasons! To be a little more clear, I've tried reversing the slashes, using /cygdrive/c/, and whatever else I could think of. But, at least we know that if you're in the directory and use -cp, it will find and launch the program. So, there's nothing wrong with the Java, just pointing the java utility at it.
Again: How is the java utility that begins the process of launching a class told to "spill its guts" on what it's doing as it's trying to load classes?
You use this construct on the JVM:
java -XX:+TraceClassPaths -cp "C:\opt\SomeDirectory\lib" myClass
I was able to get confirmation of what Java was using, not only for my CLASSPATH, but "internally" by using the above.
The fact that it echoed back both what I was doing and what it was doing somehow gave me the insight to check everything about it. Java itself doesn't work (at all) if it's installed in a location that it thinks has a link in it, and it's own fetches go right back to the system disk specification.
From that I found that Java on Windows won't take a CLASSPATH that has a link in it!
Simply ensuring that the whole tree was specified "from the top" of the drive it's on works. If it's not, it won't.
It's now working happily using the syntax noted above.
This is quite different from every other application I've seen on Windows. But, well, it's Java!
This really came from a pointer from Mark Rotteveel who commented above about this article: How to track when class is loaded and destroyed in jvm? And therein I learned how to get the list of all the options the presently in-use JVM supports. All Java developers should be aware of this in my opinion, so thanks to Mark for that.
I need to send a project made by JavaFX SDK 16 and Java SE-15 using Eclipse to my friends, but when I try to export it, i'm getting surprised that Eclipse doesn't insert the VM arguments to the exported file :
and as you know since JavaFX SDK 10, JavaFX libraries are not anymore part of the Java SE, so we need to tell Eclipse where to find them by VM arguments, in short words, these VM arguments are really important to run my program.
I already know that I can insert those arguments while using prompt command to open it, but is there a more simple way? just by clicking on the exported file ?
Your main problem is that you are trying to do something that does not make any sense. Runnable jars are not a proper distribution format for JavaFX applications for various technical reasons. The way to go is having a look at jpackage. That's the proper way of dealing with distribution nowadays. Otherwise your are just banging your head against a wall.
Here is a good summary of all the options you have: https://stackoverflow.com/a/68823040/4262407
I have this problem 5 years ago (I use netbeans IDE, so I don't know if it works in eclipse, but I think yes), and I cant find a good way to do this.
Instead, I created one Swing application, and put all code of JavaFX inside.
You could see how I do in
this link from Oracle.
In particular - the Applet.class. How could I find where it locally resides? I have tried the following, but I get an exception:
System.out.println(JApplet.class.getProtectionDomain().getCodeSource().getLocation().getPath());
It is of course somewhere in Program Files/Java/jdk_7_xx/ but I have had quite a look around and searched online and cannot find the answer. I have always wondered where specific classes reside on the system.
Note: If you want some more detail (not necessary to read below this):
What I specifically want to do is edit the Applet.class and point my Eclipse to a new JRE System Library that contains the edited Applet.class. In theory this sounds plausible, yet in practice I am unsure.
This is needed so I can test legacy code which keeps making calls to super methods - I have tried many frameworks/approaches and tried multiple possible solutions that have been posted on stack overflow and other online resources - none work.
Found the JApplet.class in C:\Program Files (x86)\Java\jdk1.7.0_25\jre\lib\rt.jar
Made a back-up of jdk1.7.0.25 on my desktop and put it in a folder Desktop\BACKUP\jdk1.7.0.25
Unzipped it (rt.jar), decompiled Applet.class with jad, changed some methods and even added a new one, recompiled it, rezipped it, replaced the old rt.jar with the new one, made a new eclipse project and made it use the JRE in Desktop\BACKUP\jdk1.7.0.25 and it worked perfectly.
..do you know how I can find the specific path of the Applet.class?
For your own PC? Sure. For the PC of a client of your applet? No.
In fact, Oracle (or was it Sun?) eventually decided it was not the business of an app. launched within the Java Plug-In (e.g. applets or JWS apps), to know where the classes were cached. Not even it that app. was fully trusted.
I'm assuming its in a jar somewhere?
Don't assume. It is set in the Java Control Panel, which defaults to 'no compression'.
I made a simple command-line based game in java, only two classes (using Eclipse). But I was wondering how I can make this into a usable application for anyone, without running it through eclipse (ie send it to someone who knows nothing about java but would still be able to play the game)? Thanks!
You want to create a runnable jar file.
Eclipse has an option for this in the "Export" menu. For more options, search for "executable jar file" here or on Google.
You want to make sure that you also include any jar files your code depends on as well (Eclipse can also do that for you).
Users will be able to start this by double-clicking on the file on most platforms. If you need better integration (such as a custom icon), you will need to bundle it up further into an OS-specific executable. But for starters, a simple runnable jar works fine.
send it to someone who knows nothing about java
You need to get them to at least install the Java runtime on their machine (if it is not already there).
Just to be clear, "command-line" and "knows nothing about java" are probably not going to work very well for you given that:
java is OS agnostic, therefore, if you send (presumably) a jar file to say...your grandma and she has a mac and you have a PC chances are her getting it to work is not going to be "out of the box easy" so to speak.
Left with this, I think you have a couple choices...first off, you do need to package your classes - a runnable jar will work fine. Aside from that, you will most likely have to build OS specific scripts (batch scripts for Windows, shell scripts for unix, etc.) and you will have to hand these out with your jar file. That being said, the intended user will still need to have java installed, and the batch scripts themselves are not likely to be trivial endeavors.
Your next option would be to use JNLP. However, I don't think JNLP has a command line mode, so you will likely have to simulate a console with something like a JTextArea.
As far as I see it, your last option it to use one of the many products (not sure if there are any free ones) that package java into native code. I think Exe4j is one such example - but, like I said, I am not sure if there are any free ones and I am not sure how hard they are to use.
Best of luck, and if you can't get your jar to work you should probably move that to its own question.
I have a major problem that happened to me. I am writing a program that has taken me 3 months+ to make and today I accidentally deleted the source code.
I am working in NetBeans and I had just cleaned and built it, so I still have the working .jar file. The program was saved on a flash drive, not my computer, so the classes are not in the recycling bin.
Can anyone tell me about how I can go about getting my source code back?
Unless you explicitly packaged your source code in the JAR file, there's no way to get back the original source. You could try using a decompiler (like this) but that will hardly give you nice, readable code.
The best solution would be to stop using your computer right now. Then use a recovery tool to recover your deleted files. The more recently it was deleted, the higher the chance you'll get it back. There are lots of tools that can be used to do this (just Google it).
You can use a decompiler ( see How to decompile a whole Jar file? ) but you won't be getting "original" source back.