InstallJava — launch the Java runtime and prepare it for use from Mathematica

ReinstallJava — quit and restart the Java runtime

UninstallJava — quit the Java runtime

JavaLink — the link to the Java runtime

JavaClassPath, AddToClassPath — the directories and jar files searched for classes

GetComplexClass, SetComplexClass — the class for representing complex numbers

SetInternetProxy — configure a proxy for connecting to the internet

ShowJavaConsole — display System.out and System.err output in a separate window

AllowRaggedArrays — whether to allow non rectangular arrays to be sent to Java

$RelaxedTypeChecking — whether to suspend type checking of arrays sent to Java