Error: Source option 6 is no longer supported. Use 7 or later?

Re
1

I want to work with the Minecraft Modcoderpack and have downloaded the associated file (version 1.8.8) and executed the decompile.bat. After a while the error: Source option 6 is no longer supported appears. Use 7 or later

After a bit of googling, I found out that it seems that it is because the JDK is a version that is too new from me, and you have to downgrade it. However, I can't download older JDK's without an Oracle account, can I?

So 2 questions:

Do I have to downgrade my JDK with such an error?
Where can I get older JDK versions from?

co

I would simply download a newer version of the pack:

http://www.modcoderpack.com/

Hopefully this should work with Java 7.