This is part of oh-my-laptop.
jEnv is a command line tools to help set the JAVA_HOME environment variable.
OpenJDK is an open source implementation of java. On mac, you could get one of available OpenJDK with homebrew.
Maven is the defacto build tool in Java world. It’s easy to install it.
Gradle is rising build tool in Java world, it is based on Groovy, so the syntax of gradle is much more simpler than maven’s old-fashioned XML.