Auto errors detection in IntelliJ IDEA

One more reason could be IntelliJ is running on power saver mode, this could be disabled following way:

File Menu -> Power Saver Mode

This is finally what worked for me! Phew! My Problem: Whenever I exit Intellij and try to open up an old/existing project, I have trouble getting the builds and execute to work on my localhost. I'm just using localhost.

Here are the steps that finally worked on my localhost environment:

1. Go to Project Structure and Select Project

a. Set the SDK to 10 (“Java Version 10.0.2”) or whatever you are using.

b. (I think this was the main step I was missing) Set the project compiler output to point to where I want the compiled output to sit: C:\Users\kbala\OneDrive - MatrixCare\SoftWLearnings\Javamyfun\NewHelloWorld\out

c. Project Language Level: I chose “SDK Default”

2. Go to Project Structure and Select Modules

a. Click on src (this is where my source code sits).

b. Then, Click on the “Sources” folder icon on the top. This adds src to the “Source folders” on the right. You will see the color change to Blue

c. Click ok.

3. Then, click on “Add Configuration” (top right corner of Intellij)

a. Select + at the top left hand corner.

b. Select “Application”

c. Change the name to “Main”

d. Now click on the Ellipsis (three dots) in “Main Class”. You should now see your Main Class. Select it.

e. You should now see the execute arrow at that top right of Intellij. And you should see the build icon (Hammer).

This should work!

If you use a build system (Maven, Gradle, etc.):

Open its panel in IntelliJ, then click the reimport button. For Gradle, this button looks like a sync icon and its hovertext says "Reload All Gradle Projects".

Why it works:

Since the build system is in charge of compiling your code, it knows which files are source code. It would be a waste of computing power to look for missing semicolons in a compiled binary file, so IntelliJ won't try to find errors until it knows the file is source code.

Most build systems, Maven and Gradle included, are also dependency managers. When you write code that uses libraries or depends on a different module, IntelliJ needs to be able to understand the dependency to tell you whether your code makes sense, or whether you made a mistake like forgetting an import statement or passing the wrong type of argument into a library function. When IntelliJ doesn't understand your dependencies, it displays all your uses of imported code in red text.

In my case none of these solutions were solving my problem, but I knew that I had been able to get error highlights when I started working on the project so I deleted the .idea folder in the project folder, reopened IntelliJ, and got back my errors. No clue as to what could have happened

I was getting the same issue, I just clicked on the re-import button on the maven panel and it solved the problem .

In my case, just Reloading the project solved it.

Right Click on Root folder -> Maven -> Reload Project

I had the same issue and here it is how I solved it: Some files where ignored and I Unignored them. To do this go to Maven tab on the right panel -> right click on each project that is in grey color and click Unignore projects.

I'll add an another reason for it. For me it was Reader mode enabled. I was not even been aware of its existence. Can be disabled in Settings -> Editor -> Reader mode.

In my case was a maven option! When you open the proyect in intellij, it create a notification.

Sometimes, this happens when the IDE is in a inconsistent or an error state.

You can find out the reason by looking at the Intellij logs from Help -> Show Log in Files and see if you see any exception there.

One possible reason could be that a plugin is interfering in the normal flow causing a buggy condition that disables the file syntax highlighting and error checking. Disabling the offending plugin should take care of that problem.

Another possible reason is that the intellij caches are corrupted in which case simply "Invalidate Caches" from the file menu should do the trick

Although I had Editor > Inspections enabled on my Settings, I had disabled it for certain files a while ago and forgot about it!

Hover the Inspections widget (compact view) in the top-right corner of the editor and select the desired highlighting level from the Highlight list.

Options:

• None: turns off all highlighting
• Syntax: highlights only syntax problems
• All Problems: (default) highlights syntax problems and problems found by inspections.

Docs:

• File and project analysis > Current file

Recently I had the same problem with Idea2025.2. The solution was to delete the ~/.local/share/JetBrains/IdeaIC2025.2 directory and re-install the plugings.