Convert "low hanging fruit" from Groovy to Java 8

[jdigger]

Per GH-125

Convert the classes that are a simple mechanical translation.

Fortunately IntelliJ IDEA has a "Convert to Java" refactoring that -- while far from perfect -- takes care of the simple syntax changes like adding semicolons.

Will likely need to keep most of the .java files under src/main/groovy for compile order purposes.