Oracle's Sun Java SE 8, a.k.a Java 1.8, is the required version to use with the Sakai. Certain files, such as *.jsp and *.jws, require compilation so downloading and attempting to use only the run time environment (JRE 8.0) will not suffice.
To confirm that Java is both installed on your system and is the correct version for Sakai, run
java -version from the command line:
If Java is installed, basic version and build information will be displayed. Example output: