Compile to java 8 bytecode

Currently all data2viz JVM jars are compiled to java 6 version (major version = 50).
Did you considered to move to java 8? Android now supports most of the java 8 features (see Use Java 8 language features and APIs  |  Android Developers)
With the newest Android Gradle plugin (7.x.x) you can even generate java 11 bytecode (see Android Gradle plugin release notes  |  Android Developers)