Netbeans 错误：无法找到或加载主类（再次）

Question

I am very experienced in Java, but not in Netbeans. I have a project that I've been working on, a little test program for a particular issue, so I have been making changes to it and running it and debugging it many times a day, every day, for several weeks. Yesterday Netbeans quit running it the way I had been running it, and I can't seem to get it started again.

The entire output when I run the project is:

run: Error: Could not find or load main class 

C:\Users\rcook\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1 
BUILD FAILED (total time: 0 seconds)

I note for whatever it's worth that the classname does not appear on the first line, as it seems to with others who have had the "could not find" error.

This happens whether I run the project (select the project and press F6) or the file (select the file and press control-F6). I have cleaned and rebuilt the project (which I didn't do often before, I've wondered if it caused the problem). I have restarted Netbeans. I have restarted the (Win7) computer. I am not running any memory-hogging programs except for Outlook, which I have been running the entire time it was working.

I can run the program from the command line by setting my default directory down to the 'classes' directory under the project and entering java stsclientexample3.STSClientExample3 .

I have checked the "Run" configuration many times -- there are no program or VM options entered, it has the correct classname. Oddly enough, if I change the classname to something that isn't there, Netbeans displays a popup that says the invalid name class wasn't found in the project, and listing the main classes available. But when I do that and select the one to run, it gives the same "could not find" error. There's one other main class in the project, if I select THAT it gives the same "could not find" error.

I have looked at the XML file referenced in the message, but it is full of ${parameter} references that I don't know the resolution of. It would likely be helpful to know how Netbeans resolves "${classname}", for instance, or even to dump the value Netbeans has at runtime somehow.

I have commented out code and re-run. Same result.

I have deleted that class from the run configuration, restarted Netbeans, and added the class back. Same result.

By now I've read more than a dozen other queries for a similar error, on SO and other places; I've tried all the things that looked at all possible (skipping things like configuring for special-purpose libraries, etc.).

Anyone know how to fix this?

---

EDIT: before someone asks, another project with a main() runs using the 'run project' option.

EDIT2: I forgot to mention, also, that another post recommended that one delete the Netbeans cache (c:\Users\\AppData\Local\NetBeans\Cache), so I shut down NetBeans, deleted everything in that directory, and restarted NetBeans. Same result.

Answer 1

I've encountered this problem a few times and it is very frustrating. If you delete the cache it should fix it after you rebuild the project

1. Close netbeans
2. Delete the Cache folder User\AppData\Local\NetBeans\Cache\ (Windows 7 and above)
3. Open Netbeans
4. Rebuild and run

Edit - you can find the cache directory also by going in netbeans to Help - About then it shows your cache directory.

Answer 2

Try creating new class with main method and copy your code into this class.

Answer 3

Just close the Netbeans. Go to C:\Users\YOUR_PC_NAME\AppData\Local\Netbeans and delete the Cache folder. The open the Netbeans again and run the project. It works like magic for me.

( AppData folder might be hidden probably, if so, you need to make it appear in Folder Options).

Answer 4

I'm working in the Netbeans IDE 8,2. I had the same problem and in my manifest.mf , the field classpath: was empty(I noticed that because I got the message:

java returned 1 could not load main class ExerciseFinal

I looked at the classpath nb where searching and I simply changed one folder's name and then after restarting netbeans everything worked.

My file name was "teo_1=1;" and I changed it to "teo" simply because I thought that maybe 1=1 (always true) was messing the nb.

Answer 5

I had the same problem and i think the problem was in the file path, either it was too long or it had some forbidden characters(now i have seen that it was a letter from my language), when i copied a project to a different folder it worked...

Answer 6

After an eternity of trying to figure it out myself, looking through every menu, submenu, tab, and option, I was still stuck. Nothing anybody suggested worked for me.

How many hours did I spend flailing about in the name of pride and self-education? Several. How long did what I'm about to suggest take? Maybe 10 minutes; 15 tops.

Was my journey a waste? No. I learned a lot. But since I hadn't set out to learn what I did and was prevented from work I needed to do, I was pissed long before giving that up and copping out.

So... Long story short, do this:

(Step 1 has been deleted; renumbering steps might be bad idea. So start with 2!)

Step 2: Open the problem project.

Step 3: Create a new Netbeans project, get into Project view, and expand both projects to show their packages.

Step 4: Thoughtfully copy all packages from problem project to new. (This means to hold off on the "main" package until last to avoid a chuteload of red-marked errors. If you see a bunch anyway, don't look at them. Further copying will fix many.)

NOTE: Having to choose a different project name for the new project will likely lead to a new name for your new "main" java class file. No problem. Just note this.

Step 5: Once you've copied all but the "main" package from problem project to new, open the "main" package to see your files. Then open the new "main" package, which will have ONE tiny file in it.

Step 6: Thoughtfully copy one file at a time (holding off on the "main" class file until last) from problem project to new.

(If you see errors, let 'em go. Not finished yet.)

Step 7: Once you have only the "main" class file left to copy from the problem project, open it. Also open the new "main" class file in the new project.

Step 8: Copy all the code from problem project "main" java class file and paste it into the new project's "main" file.

Step 9. There will be errors at the end. After all, at least one package and one file name changed. So open each source file with an error, put the cursor on each line with error, and press Alt-Enter to get a hint. Renaming the new main file or changing some old package names to new will fix a few, especially in some imports; this might just get rid of the rest.

I hope this helps someone. I should look for a more recent post and put this Answer there, if it gets enough upvotes.