Netbeans - Error: Could not find or load main class

问题

So I\'m making a java application in Neatbeans 7.4, been working at it for a while, everything was fine, running the project worked fine, but now when I hit run project, I get the error

Error: Could not find or load main class phleveledit.MainWindow
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

I can\'t think of what I did right before this started happening, so I don\'t know what I should change.. The code doesn\'t appear to have any errors. Here\'s a screenshot of the IDE+project folder

Image (http://puu.sh/5ldYB) :

Any ideas?

Edit: Unfortunately I happened to fix this problem by removing some code, which probably had some errors Netbeans couldn\'t detect, but I don\'t know what was exactly wrong so can\'t vote on a correct answer.

回答1:

1. Right click on your Project in the project explorer
2. Click on properties
3. Click on Run
4. Make sure your Main Class is the one you want to be the entry point. (Make sure to use the fully qualified name i.e. mypackage.MyClass)
5. Click OK.
6. Clean an build your project
7. Run Project :)

If you just want to run the file, right click on the class from the package explorer, and click Run File, or (Alt + R, F), or (Shift + F6)

回答2:

You can :

• RightClick on project node and go to Set configuration
• Select the main class for your application.
• Then clean and build.

Even if the above steps don't work for you then then delete the Netbeans cache by deleting the (index) folder

User\.netbeans\SOME_NUMBER_reflecting_your_version\var\cache\index\

回答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).

回答4:

Sometimes due to out of memory space error, NetBeans does not load or find main class.

If you have tried setting the properties and still it is not working then try

1. Select the project from the project explorer
2. Click on Run in the Menu Bar
3. Click on Compile

It worked for me.

回答5:

This condition happens to me every 6-months or so. I think it happens when closing NetBeans under very low memory conditions. I discovered that it could be easily corrected by (1) Rename your project, including its folder name using right-click on project explorer's project name---I put a simple suffix on the original name ("_damaged"). (2) Try BUILD. If that is successful, which it is for me, give three cheers. (3) Repeat step (1) to restore the original project name. BUILD and RUN should start without trouble. I guess that the 'rename the project and folder' process causes a special rediscovery of the applications main location.

回答6:

Try to rename the package name and the class/jframe names... The clean and build the application.

1. Right Click on the package name
2. Go to Refactor
3. Select Rename
4. Give it a meaningful name, preferably all in small letters

5. Click on Refactor

   Do the same for the class/jframe names.

6. Last Select Run from Menu 7.Select Clean and build main project

That should do it!!! All best

回答7:

I had the same issue once. The problem was not in the code. The cause was... renaming the project folder to some other non supporting name. My project name was "MobStick" and I renamed it to "MobStick - May 26, 2014 04:00PM". Renaming it back to normal solved my problem.

回答8:

I have run into this error a couple of times as well and for me the above solutions did not work. What does seem to work is going to the Project Properties, and under Compiling toggling Compile on Save.

回答9:

I found the following steps useful:

1. Right-click on the project in the left toolbar.
2. Hover over the 'Set Configuration' item.
3. Click on 'Customize...'
4. Click on 'Browse...' by the 'Main Class:' item.
5. Select the correct class.
6. Click 'Select Main Class'.
7. Click 'OK'.

My problem was that, apparently, my package name was being listed twice. Selecting the class using the dialog changed 'aclass.MainClass' to just 'MainClass'.

Hope this helps,

-HewwoCraziness

Edit: This is expanding on Mary Martinez's answer.

回答10:

Using NetBeans 8.1, I got the dread

Error: Could not find or load main class 

from carelessly leaving an empty line in the Project Properties > Run > VM Options field. Until you click in the field, you may not see the caret flashing out of place. Remove the empty line to restore equanimity.

回答11:

I just ran into this problem. I was running my source from the command line and kept getting the same error. It turns out that I needed to remove the package name from my source code and then the command line compiler was happy.

The solutions above didn't work for me so maybe this will work for someone else with a similar problem.

回答12:

I had the same problem, I had the package and class named the same. I renamed the class, then clean and build. Then I set the main class in the "run" under the properties of the project. I works now.

回答13:

You can solve it in these steps

1. Right-click on the project in the left toolbar.
2. Click on properties.
3. Click on Run
4. Click the browse button on the right side.(select your main class)
5. Click ok

回答14:

1. close netbeans.
2. open netbeans again.
3. choose new project>>java application.
4. click next.
5. deselect create main class.
6. now make the application clean build run

For more reference watch this video

回答15:

try this it work out for me perfectly go to project and right click on your java file at the right corner, go to properties, go to run, go to browse, and then select Main class. now you can run your program again.

回答16:

if you are on window os, then try to start NetBeans via administrative mode. right click on NetBeans icon and "Run as Administrative".

回答17:

If none of the above works (Setting Main class, Clean and Build, deleting the cache) and you have a Maven project, try:

mvn clean install

on the command line.

回答18:

Had the same problem here. Usually Clean and Build solves much of the problem. It happened to be caused by a wrongly installed plugin.

回答19:

I had the same problem and I moved the project to a location where the path had no none-english letter and that fixed the problem

来源：https://stackoverflow.com/questions/20034377/netbeans-error-could-not-find-or-load-main-class