1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
|
\name{jnull}
\alias{.jnull}
\alias{is.jnull}
\title{
Java null object reference
}
\description{
\code{.jnull} returns a \code{null} reference of a specified class
type. The resulting object is of the class \code{jobjRef}.
\code{is.jnull} is an extension of \code{is.null} that also returns
\code{TRUE} if the supplied object is a \code{null} Java reference.
}
\usage{
.jnull(class = "java/lang/Object")
is.jnull(x)
}
\arguments{
\item{class}{fully qualified target class name in JNI notation
(e.g. \code{"java/lang/String"}).}
\item{x}{object to check}
}
\value{
\code{.jnull} returns a Java object reference (\code{jobjRef}) of a
\code{null} object having the specified object class.
\code{is.jnull} returns \code{TRUE} if \code{is.null(x)} is
\code{TRUE} or if \code{x} is a Java \code{null} reference.
}
\details{
\code{.jnull} is necessary if \code{null} is to be passed as an
argument of \code{\link{.jcall}} or \code{\link{.jnew}}, in order to be
able to find the correct method/constructor.
Example: given the following method definitions of the class \code{A}:
\itemize{
\item \code{public static void run(String a);}
\item \code{public static void run(Double n);}
}
Calling \code{.jcall("A",,"run",NULL)} is ambiguous, because it is
unclear which method is to be used. Therefore rJava requires class
information with each argument to \code{\link{.jcall}}. If we wanted
to run the String-version, we could use
\code{.jcall("A",,"run",.jnull("java/lang/String"))}.
\code{is.jnull} is a test that should be used to determine whether a
given Java reference is a \code{null} reference.
}
\seealso{
\code{\link{.jcall}}, \code{\link{.jcast}}
}
\examples{
\dontrun{
.jcall("java/lang/System","I","identityHashCode",.jnull())
}
}
\keyword{interface}
|
