IntelliJ shows decompiled .class file instead of source code

1. Get the source files

Make sure you have downloaded and installed the source files of the JDK.

I'm on Arch Linux and installed them with pacman -S openjdk8-src which put a src.zip into /usr/lib/jvm/java-8-openjdk/. We'll use that zip file in the next step.

To list source packages of different JDK versions, do pacman -Ss "openjdk.*-src".

See this question on how to get the source files for your specific platform.

2. Point IntelliJ to the source files

In your module settings (open them with F4) under "Platform Settings" → "SDKs" → "Sourcepath", add the zip file containing the JDK source to your project JDK (be sure to pick the right JDK if IntelliJ lists more than one JDK) using the button with the plus sign:

3. Jump into the source

Select a JDK class, like Comparator, using IntelliJ's Search Everywhere or Ctrl+b with the cursor on the name of the class.

I also have the same problem. The problem for my case is that Project SDK is set to 13 [Invalid]. After I can Project SDK to a valid SDK. My problem is solved.

I tried all the things mentioned at other places for this but at the end I was doing a silly mistake. Intellij was pointing to JDK 11 for which there was no source code (I had both the SDKs 8 & 11). I removed JDK 11 and pointed to JDK 8. JDK had the source code, thus now I can see the source code on ctrl click. Also, I had disabled the bytecode viewer and decompiler plugins. Hope this helps some one.