GetJVM[link] returns the JVM expression that corresponds to link, which was returned from InstallJava.

JavaLink[] returns the MathLink LinkObject that is used to communicate with the J/Link Java runtime.

JavaObject[] is used to denote an expression that refers to an object residing in Java.

JavaObjectQ[expr] gives True if expr is a reference to a Java object or Null, and gives False otherwise.

LoadedJavaClasses[] returns a list of the classes currently loaded into Java by Mathematica.

LoadedJavaObjects[] returns a list of the Java objects that have been sent to Mathematica (and not yet released with ReleaseJavaObject).

MakeJavaExpr[expr] constructs a new Java object of the J/Link Expr class that represents the Mathematica expression expr.

Periodical[id] returns information about the periodical task corresponding to the specified integer id.

Periodicals[] returns a list of integer ID numbers corresponding to the set of operations that are periodically performed automatically when the kernel is not busy with ...

ReinstallJava[] is a convenience function that calls UninstallJava followed by InstallJava.