#75 Invalid class file format in cewolf.jar

[Anonymous]

error: Invalid class file format in cewolf.jar
(de/laures/cewolf/DatasetProducer.class). The
major.minor version '47.0' is too recent for this tool to
understand.
1.java:7: Class de.laures.cewolf.DatasetProducer not
found in import.
import de.laures.cewolf.DatasetProducer;

what is this error message.