# Java IDL: IDL to Java Language Mapping

This release of the JavaTM 2 Platform, Standard Edition, v.1.4, 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. Depending on the command-line options used, the `idlj` compiler 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, ptc, 00-01-08, with the revisions indicated in ptc/00-11-03, The new IDL to Java Mapping Chapter. Version 00-01-08 of the IDL to Java language mapping is aligned with CORBA version 2.3.2. For a basic summary of the IDL to Java mapping, see IDL to Java Language Mapping Overview below.

- The CORBA technology shipped in J2SE v.1.4 conforms to the mappings specified by the following document: Official Specifications for CORBA support in J2SE 1.4.

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

- Section 1.13, Mapping for Value Type
- Section 1.14, Value Box Types
- 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). The syntax and semantics of OMG IDL are defined in Chapter 3 of the CORBA/IIOP 2.3.1 Specification. The IDL-to-Java compiler, `idlj`, maps the IDL-defined interfaces to Java classes and interfaces as defined in OMG IDL to Java Language Mapping Specification, ptc, 00-01-08, and as supported in this version of the Java platform, as described in Official Specifications for CORBA support in J2SE 1.4.

This overview shows the correspondence between OMG IDL types and Java types. 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 Type | Java Type
--- | ---
module | package
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
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
constant (within an interface) | fields in the Java signature interface for non-abstract, or the sole Java interface for abstract
exception | class
Any | org.omg.CORBA.Any
type declarations nested within interfaces | "scoped" package
typedef | helper classes
pseudo objects | pseudo interface
readonly attribute | accessor method
readwrite attribute | accessor and modifer methods
operation | method

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