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Java IDL: IDL to Java Language Mapping

This release of the Java^TM 2 Platform, Standard Edition, v.1.3, includes idlj, a compiler that reads an Object Management Group (OMG) Interface Definition Language (IDL) file and translates it, or maps it, to a Java interface. The idlj compiler also creates stub, skeleton, helper, holder, and other files as necessary. These .java files are generated from the IDL file according to the mapping specified in the OMG document (pdf format) OMG IDL to Java Language Mapping Specification, formal, 99-07-53. The postscript version of this specification can be found at http://www.omg.org/technology/documents/formal/omg_idl_to_java_language_mapping.htm. Formal specification 99-07-53 of the IDL to Java language mapping is aligned with CORBA version 2.3. For a basic summary of the IDL to Java mapping, see IDL to Java Language Mapping Overview below.

Some topics from the OMG IDL to Java Language Mapping specification that are not easily summarized are:

Section 1.19, Mapping Pseudo-Objects to Java
Section 1.20, Server-Side Mapping
Section 1.21, Java ORB Portability Interfaces

IDL to Java Language Mapping Overview

CORBA objects are defined in OMG IDL (Object Management Group Interface Definition Language). J2SE v1.3 includes idlj, the IDL-to-Java compiler that maps the IDL-defined interfaces to Java classes and interfaces.

This overview shows the correspondence between OMG IDL constructs and Java constructs. Note that OMG IDL, as its name implies, defines interfaces. Like Java interfaces, IDL interfaces contain no implementations for their operations (methods in Java). In other words, IDL interfaces define only the signature for an operation (the name of the operation, the data type of its return value, the data types of the parameters that it takes, and any exceptions that it raises). The implementations for these operations need to be supplied in Java classes written by a Java programmer.

The following table lists the main constructs of IDL and the corresponding constructs in Java.

IDL Construct

Java Construct

module

package

interface (non-abstract)

signature interface and an operations interface, helper class, holder class

interface (abstract)

signature interface, helper class, holder class

constant (not within an interface)

public interface

boolean

boolean

char, wchar

char

octet

byte

string, wstring

java.lang.String

short, unsigned short

short

long, unsigned long

int

long long, unsigned long long

long

float

float

double

double

fixed

java.math.BigDecimal

enum, struct, union

class

sequence, array

array

exception

class

readonly attribute

accessor method

readwrite attribute

accessor and modifer methods

operation

method

IDL Construct	Java Construct
module	package
interface (non-abstract)	signature interface and an operations interface, helper class, holder class
interface (abstract)	signature interface, helper class, holder class
constant (not within an interface)	public interface
boolean	boolean
char, wchar	char
octet	byte
string, wstring	java.lang.String
short, unsigned short	short
long, unsigned long	int
long long, unsigned long long	long
float	float
double	double
fixed	java.math.BigDecimal
enum, struct, union	class
sequence, array	array
exception	class
readonly attribute	accessor method
readwrite attribute	accessor and modifer methods
operation	method

Note: When a CORBA operation takes a type that corresponds to a Java object type (a String, for example), it is illegal to pass a Java null as the parameter value. Instead, pass an empty version of the designated object type (for example, an empty String or an empty array). A Java null can be passed as a parameter only when the type of the parameter is a CORBA object reference or value type, in which case the null is interpreted as a nil CORBA object reference.

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