Two things:
1. Have you installed JDK? In other words, did you following the "Getting Java" section in the following doc?
https://wpilib.screenstepslive.com/s...eclipse-c-java
2. Also, did you following the section "Setting up JDK in eclipse" section of the above doc?
In general, take a look at the above doc and make sure you have followed the instructions to get everything set up. The error you have means eclipse doesn't know where to find the Java compiler. So either you haven't installed it or you haven't told Eclipse where to find it.