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

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.

RemovePeriodical[id] removes the computation corresponding to the integer id from the set of operations that are periodically performed automatically.

SetField[obj@field, val] sets a value of an object field.

UseFrontEnd[expr] evaluates expr in an environment where the kernel can make use of the services of the notebook front end.

CallingConvention is an option to DefineDLLFunction that specifies what calling convention the DLL function uses.