I have no idea why, but from today Eclipse doesn't compile .java files into .class. I press the "Run" button and Eclipse only tries to run the program rather then compiles it first, so i get this error all the time:
Exception in thread "main" java.lang.NoClassDefFoundError
open problems view from window -> show view -> problems, if there's any error, fix it
eclipse will reject to compile if there is any problems in your project
Close Project -> Open Project -> Clean -> Refresh
Hope it helps for someone else
This problem happens when "for some reasons" your project is corrupted and has a red icon near the project's name in Eclipse. The solution is to save the project's folder, delete the project in Eclipse, than create the project again in Eclipse coping all the previous files saved.
I ran into this problem with Eclipse Luna, for some reason the Java builder was missing from the project. Verify that in your .project file you have something like
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
You can also configure builders from Project Properties -> Builders
When I have had this exact same problem, its cause has always been the same and the solution has worked 100% of the time for me. It's caused by a missing jar file in the project's Java build path and it's indicated by a red exclamation point decoration on the project icon. To fix the problem, go to Project|Properties|Java Build Path, click on the Libraries tab and either remove or fix the path for all missing jar files. If your project is configured to rebuild automatically, it should start a build as soon as you apply your changes.
The eclipse needs to erase the output folder when building classes.
The folder is found on Project Properties -> Java Build Path -> Default Output Folder. It can differ from general output folder name found under Eclipse Preferences. If this output folder cannot be erased for some reason (for instance, on Windows, when a shell is opened on this location), the project is marked as corrupted (as Marco Micheli describes) and the classes then are not built.
You just need to make sure the output folder can be erased.
Yes I was facing this issue. Coz Eclipse cannot build the project for Build Path error. Check that your external jar files is not showing any error. Delete the Jar file which one is missing or which one is showing re color. delete that one. add a fresh one from the correct path or location. if all the error are gone. then in the project bin folder one class file will be created and then could not load main class error will be removed too.
there can be errors in your project, or other reasons like mentioned in above answers.
or you may be a fool like me
who moved the source code to other folder and not updated source path in project build properties. in this case it was not giving any error or class files too.
check that too.
goto
Project Properties -> Java Build Path -> Source
Add or Link new source folder location.
Do clean all projects ! This will erase all old class files, so eclipse is forced to generate them again.
Some times jars in the build path might be missing even though we are not using it. Since error is there, java files wont compile into classes.
Can check errors from problems view.
Either remove jars from build path or place the missing jars in the build path.
I had problem in eclipse for load module not found and no class file was getting created.
Solution: Go to Create New Project > Under JRE section Choose Use project Specific JRE.
Now Class files are created.
Please check if all the jars are there in your build path settings.
If any jar is missing this issue might come.
I had this problem, I tried the clean, the build manually, open, closing the project, deleting, and open, etc., nothing works, and after 4 hours I get a workaround what works for me.
Please, Make a RAR, ZIP, or copy from your entire project folder as a backup if it doesn't work and you mess around, OK, now:
Clean the Project. It cleaned all my class files from the output folder, but doesn't generate the class files after the clean with the building (but we already know that)
Delete the project (warning, make sure the Delete contents is not selected or your project will dissapear). For me it says something about that desynchronysation with code mix, and hibernate, blabla)
Close myEclipse
Restart your computer.
Open myEclipse
Import the project with the option "Projects from folder or Archive", not with the "existing projects into workspace" option.
Myeclipse start to build the class files, I don't know why, but works for me, I hope this helps somebody else.
Also ensure that there are no projects with fatal errors (projects with ! symbol over it) in the build path of the project which is not generating classes under the bin directory
Just restart your machine.
Its weird but it helps we had loads of problems this type in our company for unknown yet reason. Always restarting the machine helped.
It was normally encountered while trying to run Junit tests and it could not find a class even when the Run configuration was pointed to /bin.
I encountered a similar problem: previously compiled and running java files couldn't run anymore. Eclipse showed "couldn't find class xxxx". When I checked bin folder, the previous .class files were gone. That's why Eclipse couldn't run the files, NOT because of errors in files. I don't know why it can't just re-compile the file, and why the .class file gone missing in the first place.
But I found a solution:
Simply create a dummy java file in the same package (without doing anything just create), then run it. Then magically all previous .class files came back. And I can run those files as before.
Just Remove Your all Jars (Libraries) from the Build Path and refresh and add all jars and clean and build the project
This is probably a rare event but I declared a servlet with annotations and left off the "/" before the servlet mapping name. I spent over an hour chasing my tail, installing new servers, thinking I might even need to re-install my IDE and it was this simple error! Every time I tried to load any page from my Dynamic Web Project I got a 404 error. I could not even load a plain vanilla html page. There really needs to be better error logging with the IDE and Server interaction as there was zero indication of the error and my servlet was never called at the start of my web app. Hope this helps save someone else some frustration. Always name your servlet with a / slash like /myServlet never just myServlet.
I tried many different potential solutions: cleaning, rebuilding, removing, re importing, Update Maven Project and nothing. I still couldn't run my app from Eclipse. In my case the reason was that I was running Eclipse using openjdk-11 while my project was in Java 8. After I've reconfigured Eclipse to be ran from Java 8 everything started to work (in eclipse.ini).
-vm
/usr/lib/jvm/jdk1.8.0_202/bin
I'll explain my solution to this problem: "eclipse not compiling java files into class files". I'm using Eclipse version '2020-03 (4.15.0)'. I have a project that is dependent on a java project. For the dependent project, I was not able to export a jar file containing the compiles classes and resources. To be more precise, the exported jar file did not contain any class files. The output bin folder for the project is empty after doing a project build. In examining the console output when I tried to build all projects indicated that the build failed because the dependent project was missing. In looking at one of the log outputs, I saw something indicating that the build failed because some eclipse class was missing.
One of the things I tried was to do an eclipse update. Eclipse offered up the list of changes and I tried to apply them, but the update failed. I tried to update several times but they all failed. Looking more carefully at the offered up list of updates I noticed that one of the suggested update involved "deleting" Java Development Tools. That line had an warning indicating that the entire feature could not be deleted due to other dependencies and that only the non dependent features would be deleted. Doesn't that sound suspicious. Why was the update trying to delete Java Development Tools? My speculation is that something got deleted from the Java Development tool that was causing the build process to fail. The missing class I saw earlier also suspiciously sounds like it might be part of the Java Development Tools feature.
So what I did to solve the problem was to reinstall eclipse. I used the eclipse loader application to do the reinstall. (Note, I did not uninstall it first). After the reinstall, the dependent project was able to produce classes, and things once again worked as they should.
I certainly don't know how the eclipse release got into this compromised state, but in my situation the re-install of eclipse was the only way I could find to resolve the problem.
There would be the case : if you have opened project explorer in eclipse then it may not show you classes generated under /**/build/classes, in such case open Navigator view of that project and check build directory under the same project.
For the reasons of electricity my computer has shut down. That time my Netbeans project was running. I built up this project a few minutes back. Starting up the computer, the Netbeans project source file is gone. How can I retrieve my project files?
You should have the project in the NetbeansProject folder.
Use open project button and it should put it back if the sources and .project are there.
So, if nbproject folder exists then you can open the project. If the src is there then you have the source files. If not you might be screwed. That's where SVN is handy.
If they are gone, then it depends on the sensitivity and importance of the code. You may need to pay a service to extract the bits from your hard drive if they are even still there.
Have you tried to select (highlight) the project that contained the ZIP file. Under Versioning, select Local History -> Revert Deleted and see if your ZIP file comes back.
I noticed that "sometimes" the resources i put into a source folder in my Eclipse project will not be copied to the output folder ("bin") immediately.
E.g. i change a properties file using the eclipse editor and save... and "bin" still has the old version.
Does anyone know what exactly triggers the copying (and how i can trigger that from a plugin)?
I thought it happened automatically when a resource changes.
-- EDIT --
To clarify what i meant by triggering it from a plugin: I have a plugin that depends on up to date resources in the output folder, but apparently the resources are outdated when my plugin is called. And that's why i need to better understand what happens and how i can force it when i need to.
If you don't add the resource through eclipse (but for instance through the windows explorer), eclipse wont notice some changes until you refresh your project/folder. (right click in the packater explorer for instance).
After it notices the change it will copy it to the output folder when you build (often this is done automatically upon changes)
This is a Bug in almost all Eclipse versions, it happens without any reason. My eclipse 3.5.2 and 3.6.2 both meet this problem in someday. In my case, I need to copy modified .clj clojure source files to classes directory for immediate effection in a web app, now I have to set /src before /classes in CLASSPATH of web appserver startup script, It's solve my problem temporarily.
As #Thirler said, if you don't add the resource through Eclipse, it may not notice the files until you refresh your project. However, if the Refresh/Clean doesn't work (in my case, it didn't), you have to add the files to the folder structure IN ECLIPSE.
Just drag the file from the folder where it is in the file system using Finder/Windows Explorer, drop it into the same folder in Eclipse's Project Explorer (Eclipse will ask for overwriting, just say yes) and Voila!
EDIT:
An easier way is to just navigate into the folder using Project Explorer and then Refresh (F5).
As far as I know it happens when you build the project. You don't need a plug-in, you just need to tell eclipse to do a build of the project.
There is an Eclipse setting Java > Compiler > Building > Output folder > Filtered resources.
For unknown reasons, this was set to *.launch,*.testsuite,*.deploy,*.location,*.execution,*.datapool,*.artifact,*.html,*.svg in my workspace (while the default seems to be just *.launch). This was the reason, why my Eclipse constantly refused to copy a classpath resource index.html.
Late response, but I just stumbled over this question but non of the answers helped me to convince Eclipse to do its job.
This happened to me when I imported an Eclipse project as a whole, including both src and bin directories. The fix is to Clean the project: Project -> Clean... -> select your project and press Clean. This should re-build the project and properly locate the resources needed.
This problem has been frustrating me for some time...
A lot of sites like Sourceforge use SVN or Subversion to manage their code. I have little problem compiling SVN code in C++, but when it comes to Java, my IDE gives me a headache.
I've installed Subclipse for SVN support for Eclipse, and it works. I can check out any code into my Workspace. Now Subclipse will put the whole thing into a special project of some sort that can't be compiled. So I search Google for something and I come up with modifying the eclipse XML file to specify the 'nature' to be a Java project.
Okay, now it's a Java project. Say I have a folder structure like:
\src
\data
\graphics
I get 800 compiler errors complaining the package name is org.company.SomePackage instead of src.org.company.SomePackage.
Then what I do is create packages called src, data, graphics, etc, instead of just folders. I cut and paste everything in the folders into the packages and finally I can compile it.
What is a better way to do this?
EDIT: I can only check out anything SVN as a SVN project, and there's no way within Eclipse to change that to a Java project. How can I check out the SVN as a java project in the first place?
I get 800 compiler errors complaining
the package name is
org.company.SomePackage instead of
src.org.company.SomePackage.
Right click on Project -> Properties -> Java Build Path -> Source Tab -> Add "src" as a source folder and remove any others.
it thinks your source is stored in root folder. you need to specify to the project that /src is the source folder.
In general when we have an Eclipse project, which contains Java code – but we didn’t set it up as a Java project when we created or checked out this project, we are struck. And Eclipse doesn’t allow to change the project type inside the Gui. So we need to add the java nature as below.
1. Close your project.
2. Open your project file (which is located in your root directory of the appropriate project) called .project with your default editor. Search for
< natures>
< /natures>
and change it to as below
< natures>
<nature>org.eclipse.jdt.core.javanature</nature>
< /natures>
Save the changed file.
3. Open the project again – now it should become a java project.
Then do the following as explained by Kevin
On the Project Explorer Window ->Right click on the specific Project -> Properties -> Java Build Path -> Source Tab -> Add "src" as a source folder and remove any others.
For me when I went into “Source Tab” – the “src” folder was already added, but it was not giving me the desired result (ie I was still not seeing the .java files in the project explorer window). So I removed the “src” filed that was already added in the Source Tab and then added them again. And then all worked fine.
You have to configure proper source paths. Some open source projects make this automatic by checking their .project and .classpath files in with the rest of their files. For others, you'll have exactly the problem you are having. You need to set the classpath so the Java compiler knows where to find the source. You right click on the project and select properties and configure an arbitrary classpath, but the answer given by Kevin is easier for a beginner.