intellij idea - Error: java: invalid source release 1.9

java intellij-idea compiler-errors

Select the project, then File > ProjectStructure > ProjectSettings > Modules -> sourcesYou probably have the Language Level set at 9:

Just change it to 8 (or whatever you need) and you're set to go.

Also, check the same Language Level settings mentioned above, under Project Settings > Project

java intellij-idea compiler-errors

Sometimes the problem occurs because of the incorrect version of the project bytecode.

So verify it : File -> Settings -> Build, Execution, Deployment -> Compiler -> Java Compiler -> Project bytecode version and set its value to 8

java intellij-idea compiler-errors

I have had the same problem. There is an answer:

1.CTRL + ALT + SHIFT + S;
1. Then go to "Modules";
2. "Dependencies;
3. Change "Module SDK".

Got it!Now u have Java 9!

CodeHunter