Hey guys!
Today I forked Java solutions and imported the project to IntelliJ. If your local Java environment is like me, installed Java 8 and Java 6, you may encounter the problem while making the project.:
Error:java: invalid source release: 7
The problem can be fixed in this way: In IntelliJ 13.1.4 I had to change Java and SDK version on the following place:
File -> Project Structure -> Module Settings -> Tab: Sources: Language Level -> 7
Here is also a great answer from stackoverflow.