javac: invalid target release: 1.8

For IntelliJ14 you may have to change the bytecode version w.r.t. the JDK you are using (in the global settings):

if you are going to step down, then change your project's source to 1.7 as well,

right click on your Project -> Properties -> Sources window 

and set 1.7 here

_{note: however I would suggest you to figure out why it doesn't work on 1.8}

1. Download JDK 8.

2. Edit your env var for JAVA_HOME to point to the new installed JDK 1.8: R-click on My Computer -> Properties -> Advanced System Settings -> Environment Variables find JAVA_HOME on the list and set it's value to something like that:

   C:\Program Files\Java\jdk1.8.0_31
   

3. Find the old version and edit it in PATH variable aswell.

4. Probably you will need to restart the system.

Should be done.

If this error occurs when running a Gradle (or Maven) task, you need to modify that build tool configuration to point to your installation of Java JDK 1.8 following this route:

File -> Settings -> Build, Execution, Deployment -> Build Tools -> Gradle

There you check the Linked Gradle project is the one you are working on and select the Gradle JVM (You missed this when you imported the gradle project into IntelliJ)

Remember when importing a Gradle (or Maven) project to set the target JVM correctly here: