rJava (version 1.0-11)

JavaAccess: Field/method operator for Java objects

Description

The $ operator for jobjRef Java object references provides convenience access to object attributes and calling Java methods.

Usage

# S3 method for jobjRef
.DollarNames   (x, pattern = "" )
	# S3 method for jarrayRef
.DollarNames (x, pattern = "" )
	# S3 method for jrectRef
.DollarNames  (x, pattern = "" )
	# S3 method for jclassName
.DollarNames(x, pattern = "" )

Arguments

x

object to complete

pattern

pattern

Methods

$

signature(x = "jobjRef"): ...

$

signature(x = "jclassName"): ...

$<-

signature(x = "jobjRef"): ...

$<-

signature(x = "jclassName"): ...

names

signature(x = "jobjRef"): ...

names

signature(x = "jarrayRef"): ...

names

signature(x = "jrectRef"): ...

names

signature(x = "jclassName"): ...

Details

rJava provides two levels of API: low-level JNI-API in the form of .jcall function and high-level reflection API based on the $ operator. The former is very fast, but inflexible. The latter is a convenient way to use Java-like programming at the cost of performance. The reflection API is build around the $ operator on jobjRef-class objects that allows to access Java attributes and call object methods.

$ returns either the value of the attribute or calls a method, depending on which name matches first.

$<- assigns a value to the corresponding Java attribute.

names and .DollarNames returns all fields and methods associated with the object. Method names are followed by ( or () depending on arity. This use of names is mainly useful for code completion, it is not intended to be used programmatically.

This is just a convenience API. Internally all calls are mapped into .jcall calls, therefore the calling conventions and returning objects use the same rules. For time-critical Java calls .jcall should be used directly.

See Also

J, .jcall, .jnew, jobjRef-class

Examples

.jinit()

v <- new(J("java.lang.String"), "Hello World!")
v$length()
v$indexOf("World")
names(v)

# \dontshow{
stopifnot( v$length() == 12L )
stopifnot( v$indexOf("World") == 6L )
# }

J("java.lang.String")$valueOf(10)

Double <- J("java.lang.Double")
# the class pseudo field - instance of Class for the associated class
# similar to java Double.class
Double$class
# \dontshow{
	stopifnot( Double$class$getName() == "java.lang.Double" )
# }