I am new to java.I have a doubt that only ".java" files supports debugging whereas the
".class" files does not supports debugging in IDE.
Can you please suggest an answer?
Most IDE's (I know eclipse does, and pretty sure IntelliJ and netbeans do) will allow you to step through the processing of a class file, however they won't let you see what code is being executed, however you can see the variables in use. However to get there you will need to add a breakpoint in your code, and step down to the relevant class file. If you can attach the source, it will let you see the code being executed, as well as add a breakpoint directly in the file in question.
Related
Do you know any way to find (un)used code from the perspective of a specific main method (or what IntelliJ calls an entry point)?
The background is that we have a big java project in which we have custom code for several clients. Sometimes we give clients the current state of the project in source form but would obviously want to remove the parts which only concern other clients. We have a Main file for each client so it should be possible to follow imports from there to find exactly the files relevant to each client.
I was hoping to be able to run intellij's code inspection on a single entry point but was unable to find anything. I'm open to any solution though.
You could remove all other entry points and run intellij's code inspection again to detect unused code. Now that you have only one entry point it should be able to tell you what code is unused. With that knowledge you can revert you changes and remove this code.
Hope that helps.
Sometimes i just want to write out some quick java to see if my algorithm works.
Maybe I am preparing for an interview! Maybe I just want to see how my code is running.
At these times, I typically make a new java file, and save it in a project i've marked called "scratchyCat". Don't judge me.
However, 99% of the code there is useless, I don't need to save it or ever even see it again. Does eclipse have some shortcut to create a java page that i can just write code on, compile and run, and then delete?
Alternatively, is there some website (like jsfiddle) that would let me do the same for java?
At first I have to say, that I've just started learning java a short while ago, so I'm not familiar with the language at all. Due to this, I try to get things done without using an IDE, so I can understand how things work. However, it's not the language that drives me crazy, but the process of making a .jar file.
I have the directories E:\Java\MyLib\mylib.java, E:\Java\Test\PartA\parta.java and E:\Java\Test\PartB\partb.java, which contains my main. mylib.java is a package that gets imported by parta.java, parta.java gets imported by partb.java.
I created a .bat file consulting several tutorials as much as the official specification from oracle about how to use the jar.exe, I've created a valid manifest.txt, I told the programm where it could find the partb.class containing my main, everything gets compiled to its own .class file just fine what tells me that my code is correct, but trying to merge all the files together into one .jar file took me hours without a working result.
According to any instructions I was able to find I'm doing everything right, I tried many different spellings and options, but at the end, either the compiler does not even find the files in the subfolders, or the files are in the .jar, but the javab.class is not able to find them during runtime.
It's sickening. I think I'm missing something, doing something absolutely wrong, but I can't figure out what it is. Any advice would be highly appreciated.
Use an IDE, it makes life so much easier. But, if you insist on doing things the old fashion way, try turning off your antivirus. If that doesn't work, check to make sure your environment variables are set correctly. If all else fails, try reinstalling your JDK.
I am writing/planning to write a program that takes in a java file (or multiple java files), and edits and adds functions/classes/variables and then outputs a new java file (or multiple files).
Is there a C++ or Java library that
Can recognize and output names of classes/functions within a text file
Can recognize and output the names of the input arguments for said classes/functions
Can allow me to insert code at specific lines or within specific functions
Can search for a given variable name/value
Maintains original file formatting
I would prefer not having to manually code something to do the above, so any help would be appreciated.
Thank you in advance!
EDIT: I currently use Eclipse, and am unsure of how to proceed. So to further explain my question:
In eclipse, if I write a program that opens another .java file, How would I go about 'asking' eclipse to output, say, all the class names of the .java file I just opened?
Also I will explain the 'purpose' of this project to further clarify. I want to write a program that can take in any java file, and turn it into a class that can implemented remotely via RMI. To do this I will need to add an execute() function, have the file implement Task and Serializable and add a few variables, etc... Based on my knowledge, doing this in Eclipse would require manual editing of the program, but I would like to completely automate this process.
Thank you, again.
Much of what you need can be found in a modern IDE; and some very good IDEs are open source (eclipse and Intellij IDEA Community Edition for Java). You might look there to see if there are modules that suite your needs.
Looks like you are talking of a tool like eclipse. You might not be looking for a full fledged IDE, but the requirements that you have mentioned are fulfilled by any basic IDE.
If you wish to make one of your own, you can do that using eclipse rich client platform.
All that you would need from Java is the reflection API.
I use Eclipse to write Java code and use DropBox to sync my code with others' across our multiple computers. Most of the time, everything works as expected: if anyone makes a change on either end, the change is saved and when the other person refreshes the Eclipse workspace, the changes come through and can be viewed and run successfully.
Sometimes, one of several errors arises. Sometimes Eclipse says it cannot find a main class and sometimes it says it could not find the class itself. Sometimes it will not report an error but for some reason will not actually update the .class file and therefore run an old version even though the compiler displays the new source code and that saves. I've then noticed that if I manually copy the code into a new .java file elsewhere in the file system and then compile it, it works fine, but for some reason it refuses to regenerate the .class file and I have to delete it manually and replace it with the one generated in the other project--then it works. But for solving the other problems everything needs to be manually copied, deleted, and re-pasted....
[The actual errors include NoClassDefFoundError, UnsupportedClassVersionError, and some other error related to not having a main class.]
I realize that the description here is somewhat vague, but unfortunately I'm not entirely sure what's going on. I hope I'm just missing some basic fact that would help solve all these problems.
Thanks!
I'm sure you will see issues using Dropbox for sharing your source.
Eclipse does not know what Dropbox is doing whilst it's uploading and downloading updates and their activities will certainly not be synchronised. At arbitrary points in time when Eclipse tries to do builds etc. it will find unexpected activity going on, maybe even partially downloaded source files which might explain the specific errors you are seeing.
You're trying to do something more complex than sharing photos or documents. The advice I would give is to use a source control system like git or subversion for source code sharing and control. You can then make use of plugins for Eclipse that are designed to integrate these systems in an easy to use way. There's a learning curve there, but the skills will serve you well.
You can use online versions of these solutions like github and unfuddle if you want to consume sharing, backup and version control of source as a service like you do with Dropbox. They're free, too.
Subversion, Git and all version control software solve all of these problems for you.
Dropbox is not really an adapted system for sharing code. What you should do is set up a SVN, and commit only the source files. This way, you won't have these kind of errors.
Dropbox does have versioning (you can restore old versions of a file), and doesn't seem to be a horrible solution for the problem. I keep my Eclipse repository on Dropbox so it is available on any computer; but since I only use it myself, I haven't encountered your problems.
There is one case I can absolutely see you running into problems--it's if your class files are stored in the dropbox as well. This would just screw everything up. Make sure you specify a location on your local hard-drive for all build artifacts (classes, jars, ...) and that the only thing on your dropbox is the .java sources.
In fact, I suggest you don't keep your eclipse project in your dropbox, just create your eclipse project and point it to the java files in your dropbox.
If this doesn't work for you, go with what other people here said and set up a SVN repository somewhere, it's easier than you would think.
Oh, another possible problem--dates! You may want to make sure the date on your java files isn't jumping forwards and backwards (as might happen if one of your developers were in another time zone). In this case, Eclipse may prefer not to re-compile your file.
Also, instead of the copy/etc procedure you are currently going through, try forcing a project clean.
Response to request for more info:
When you start Eclipse, select/create a workspace that is NOT on your dropbox. The best place is probably off your home directory. If you have already specified a default workspace, there should be a switch workspace item in the file menu.
Create your project. select "Create project from existing source" and specify the source files in your dropbox. I think you want "create separate folders for source and class files" to keep your class files out of your dropbox. If you see anything saying "Copy files into your workspace, say "no".
This should give you a valid, working project. I hope you don't see those problems any more.
One more thing may help--and this may work on your existing project--without the above procedure...
Whenever you refresh your files (f5) to load in changes from the dropbox, select the Project/clean menu and select the project. This should delete all the class files and rebuild them.
If your classfiles are shared on the dropbox, this could still have strange consequences on other people with eclipse open, so I really do suggest rebuilding your workspace as I said above.
How to avoid no main class
Provide one. That issue has nothing to do with DropBox