rJava: accessOp – R documentation

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accessOp

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

Arguments

`x`	object to complete
`pattern`	pattern

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.

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"): ...

Examples

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



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

rJava

Low-Level R to Java Interface

v1.0-4

LGPL-2.1

Authors

Simon Urbanek <simon.urbanek@r-project.org>

Initial release