Develop Reference

IntelliJ IDEA: "cannot resolve symbol" for String, System and other Java classes

I recently downloaded IntelliJ IDEA to a different computer. On one computer it works fine on the other computer it is giving me this current issue.
When i open a new project with a template it automatically shows errors everywhere even though it allows the code to run and shows the output correctly: standard Java library classes like String and System are highlighted in red and the error tooltip says: "cannot resolve symbol".
I have tried "Invalidate caches/Restart", but it didn't help.

Check the JDK configuration Classpath tab in Project Structure | SDKs:
Also check that project and modules use the same JDK.
If it's empty, remove the JDK and add it again. It's not recommended to use JetBrains Runtime as your JDK, download and configure some different standalone JDK instead, 2020.1 version can download JDK for you.
Important notice
The bundled JRE is used for running the IDE itself,
and it's not sufficient for developing Java applications. Before you
start developing in Java, download and install a standalone JDK build.

I tried above, but no luck. I did get it working with File -> Invalidate Caches...
I selected all three checkboxes and then "Invalidate and Restart". That worked for me.

Often this means there is an issue with your java compiler. Normally this issue arises on an initial Intellij install. You can install/update the java compiler to get it working properly.
Go to the editor and type Ctrl + Alt + Shift + A . Then, a little bar pops down and you can select to either install the compiler, or configure it. Both times this happened to me, I just clicked install and once it was done, everything worked. If the install doesn't work, you can just reconfigure your compiler.

Removing the Java SDK and adding it back under File->Project Structure did it for me.

The only thing that worked for me (after hours of trying!) was to use the Android Studio's embedded JDK. "Invalidate caches/Restart" did not solve the issue, even using the same JDK version which was not coming with Android Studio was giving the Cannot resolve symbol 'String' errors. Wonder what's so special with this pre-packaged JDK! Hmmm

For me the solution seems to have been creating a new Run Configuration.
I had tried deleting the SDKs, and re-adding the one I needed but that did not clear the error. But creating a new Run Configuration did the trick.

I had this problem when I uninstalled JDK and re installed it, and when I was making a new project I had the uninstalled JDK file selected, which somehow caused the system to be in red and un run-able.

Gradle sync fail for a Grails project in IntelliJ IDEA

I'm using IntelliJ IDEA 2017.3 and having trouble with a basic project in Grails in it - when Gradle starts syncing the project after starting up the IDE, all the checkmarks are green and labeled as "OK", my Messages tab is empty but still I get an alert on top of the editing pane reading "Gradle project sync failed. Basic functionality (e.g. editting, debugging) will not work properly".
I've tried removing the .gradle folder, the Restart and Invalidate option, giving IntelliJ a local path to Gradle as opposed to just telling it to use the default - all to no avail. I'm behind a corporate proxy but it is set up in IntelliJ so it shouldn't be blocking anything (especially since all the syncing seems to be working just fine).
What could be the problem? Versions of my stack:
Grails Version: 3.3.8
Groovy Version: 2.4.15
JVM Version: 1.8.0_181
Gradle Version: 3.5
I've tried ensuring that proxy's not the problem according to #dkb suggestion but it does not seem to be malfunctioning - I did Invalidate and Restart again and after running bootRun, Gradle correctly downloaded Apache Ant to run the application so it doesn't seem likely to be the culprit here.
IntelliJ also kept nagging me for Android SDK (who knows why but OK) which I could not install "normally" in the corporate setting but in the end I did provide it through IDEA's Settings -> System Settings -> Android SDK -> Edit and downloading some arbitrary API and the SDK tools through there so it shouldn't be the problem either (or at least I presume it shouldn't).
In line with #y.bedrov's suggestion, I am attaching the log after reproducing the issue (external link cause it exceeds SO's post character limits).

How to configure Grails for Netbeans?

I am trying to configure Grails in Netbeans.
Grails version:3.2
Netbeans: 8.2
JDK: 1.8
OS: Windows 10
I have install and configured environment path and other stuffs. I can create and run project from the Command Prompt. But I can not create project from netbeans.
Warning |
Unrecognized flag: non-interactive.
Error |
Specify an application name or use --inplace to create an application in the current directory
This error is showing, to create project from Netbeans. I can run the created project though. I have already added Groovy plugin.
How can I solve this problem?

I don't think you are doing anything incorrectly. I have an environment very similar to yours (Grails version: 3.3.2, Netbeans: 8.2, JDK: 8u151, OS: Windows 10) and I see the same error: Specify an application name or use --inplace...
This is a known issue with NetBeans 8.2 that has already been bug reported; see Bug 258407 - Error when creating a Grails 3.1.x project. The problem has been confirmed to exist in Grails releases 3.1.0 up to 3.1.4, but I see the same issue in 3.3.2, and there is no fix for NetBeans 8.2.
However, I successfully created a Groovy/Grails application using JDK 8u151 with a DEV release of NetBeans which you can download from here: http://bits.netbeans.org/download/trunk/nightly/latest/
Note the caveat that comes with using DEV releases of NetBeans:
These builds are still under development and could contain defects
that lead to data loss. They are meant for evaluation of new features.
As always, be sure to back up your changes if you use these builds on
your production code.
As long as you can you can live with that situation, using a DEV release is your (only) solution for creating Grails 3.x applications in NetBeans.
One final point: unlike NetBeans 8.2, DEV releases of NetBeans support Java 9 as well as Java 8, but don't use Java 9 when creating a Groovy/Grails applications. It won't work for a completely unrelated reason.

I'm using Windows 8 and Grails 3.3.8, but the following worked for me:
Create the project using system command line (I used instructions in this page: how to create grails project through windows command promt).
Import the project to Netbeans 8.2 by clicking on File > Open Project... and selecting the project folder.

This solution works for me (Mac OS)
1) Open de console inside Netbeans
2) Navigate to your GRAILS_HOME/bin
3) Type grails create-app [YOUR_NAME_APP] --profile=web (rest-api, etc)
4) The project must be created at GRAILS_HOME/bin/[YOUR_NAME_APP]
5) Do not try to import into Netbeans instead of it Open the project
6) Start coding!
You can move the folder GRAILS_HOME/bin/[YOUR_NAME_APP] to the Netbeans workspace before open the project.

FYI, I am using netbeans 9 and grails 3.3.8 (dont use 3.3.9, its broken), and it works like a dream. I can create domain classes etc. from the menus in netbeans, run, debug etc. THe only thing I had to do was manually install the grails plugin for netbeans, and configure my grails paths etc. The answer on how to set this up is here: how to open a grails 3.3 app in netbeans 9?
The only thing I cant get to work (and its a bit of a show stopper), is multi-module projects (i.e. a grails app which depends on a grails plugin). I can run them, but netbeans does not recognise any of the imports so there is no code completion and it shows all files are having errors. What a shame, as appart from this, netbeans has very good grails support.
Note, I always create projects on the command line, e.g. "grails create-app myapp ...", then simply use the open project menu in netbeans and it instantly recognises them as grails.

Ensure you have gradle plugin installed for netbeans. Then go to File -> Open Project.
You should see the project shown by netbeans as a gradle project.

Eclipse-PMD : error while installing through eclipse market place

I'm trying to install the PMD source code analyser plugin for Eclipse. It's available through Eclipse Market Place, but I'm getting following problem in the phase of installation :
Why am I getting this problem ?
EDIT
I do not have this menu even though I have added the ruleset configuration file

I'm the creator of eclipse-pmd, the plugin you are trying to install. I tried to install it myself just now and it worked without any problems. So I can only guess what could be the problem in your case:
The repository was temporarily not available
Simply try again.
You are using a (very) old version of Eclipse
The plugin requires Eclipse Indigo (3.7) or later. I tried to install eclipse-pmd with Indigo and Luna just now and it worked both times.
Run Eclipse with Java 7
You need to run Eclipse with a JRE 7 or later. There have been problems during the installation with people using an older JRE in the past. However they could finish the installation but Eclipse silently refused to load the plugin (this has been fixed a few versions ago though).
Proxy configuration
Although unlikely as you came this far, please open the proxy configuration in Eclipse and check if the settings are correct and the domain is accessible.
If you tried everything I suggested above and are still not able to install the plugin, please head over to the project's Github page and open an issue.

Netbeans suddenly failed to start after saying "Done Loading modules"

Netbeans 8.0 fails to start in Ubuntu 12.04 suddenly. Previously it used to work fine. But now it does not start, when I try to start, the netbeans blue loading box shows up, sometime after showing the message "Done Loading modules", it disappears & netbeans windows does not appear. However netbeans is still shown in the running processes, but the netbeans windows does not open after any time.
In the past, this also happened with netbeans 7.4 sometime ago when I disabled some plugins (probably it was due to disabling some Hudson plugin/Husdon UI plugin). But now this time it is probably after an automatic update of a plugin, I don't know which one now. I tried remove the entire cache directory as well but no improvement to situation. Is reinstalling netbeans, the only solution each time(Huh!) ?
Edit:
Sometimes it works when I run from terminal using(worked for netbeans 8.0 but not for 7.4):
$ /bin/sh /home/user/netbeans-8.0/bin/netbeans

I have experienced this before with Netbeans 7.4 and 8 on Ubuntu 12.04 x64 and on Windows 7 SP1 x64. The only way I could solve it was by removing Netbeans and its cache, and then reinstalling it. Maybe it's a rigorous solution, but it's a solution.
However, maybe you can check your logs and see if there is an exception somewhere. It could be helpful to at least report an issue to the Netbeans developers (or plugin developers, if a plugin is the culprit), so your particular issue (and possibly mine) can be fixed. Off the top of my head, the Netbeans startup log for Ubuntu is located at /home/<user>/.netbeans/8/var/log, you could check that out.
Another way to go is to reinstall Netbeans and add your plugins one by one. That way you can root out the culprit and address its developers.