Provides the mapping of the OMG CORBA APIs to the JavaTM programming language, including the class `ORB`, which is implemented so that a programmer can use it as a fully-functional Object Request Broker (ORB).

For a precise list of supported sections of official CORBA specifications with which the Java[TM] Platform, Standard Edition 6 complies, see Official Specifications for CORBA support in Java[TM] SE 6.

# General Information

The information in this section is information relevant to someone who compiles Interface Definition Language (IDL) files and uses the ORB to write clients and servers.

The classes and interfaces described in this section can be put into four groups: `ORB classes`, Exceptions, `Helper` classes, and `Holder` classes.

## The `ORB` Class

An ORB handles (or brokers) method invocations between a client and the method's implementation on a server. Because the client and server may be anywhere on a network, and because the invocation and implementation may be written in different programming languages, an ORB does a great deal of work behind the scenes to accomplish this communication.

Most of what an ORB does is completely transparent to the user, and a major portion of the `CORBA` package consists of classes used by the ORB behind the scenes. The result is that most programmers will use only a small part of this package directly. In fact, most programmers will use only a few methods from the `ORB` class, some exceptions, and occasionally, a holder class.

### `ORB` Methods

Before an application can enter the CORBA environment, it must first:

- Be initialized into the ORB and possibly the object adapter (POA) environments.
- Get references to ORB object (for use in future ORB operations) and perhaps other objects (including the root POA or some Object Adapter objects).

The following operations are provided to initialize applications and obtain the appropriate object references:

- Operations providing access to the ORB, which are discussed in this section.
- Operations providing access to Object Adapters, Interface Repository, Naming Service, and other Object Services. These operations are described in Other Classes.

When an application requires a CORBA environment it needs a mechanism to get an ORB object reference and possibly an OA object reference (such as the root POA). This serves two purposes. First, it initializes an application into the ORB and OA environments. Second, it returns the ORB object reference and the OA object reference to the application for use in future ORB and OA operations.

In order to obtain an ORB object reference, applications call the `ORB.init` operation. The parameters to the call can comprise an identifier for the ORB for which the object reference is required, and an arg_list, which is used to allow environment-specific data to be passed into the call.

These are the `ORB` methods that provide access to the ORB:

- `<bold>init</bold>()`
- `<bold>init</bold>(String [] args, Properties props)`
- `<bold>init</bold>(Applet app, Properties props)`

Using the `init()` method without parameters initiates a singleton ORB, which can only give typecode creation `any`s needed in code generated in Helper classes by `idlj`.

Applications require a portable means by which to obtain their initial object references. References are required for the root POA, POA Current, Interface Repository, and various Object Services instances. The functionality required by the application is similar to that provided by the Naming Service. However, the OMG does not want to mandate that the Naming Service be made available to all applications in order that they may be portably initialized. Consequently, the operations shown in this section provide a simplified, local version of the Naming Service that applications can use to obtain a small, defined set of object references which are essential to its operation. Because only a small well-defined set of objects are expected with this mechanism, the naming context can be flattened to be a single-level name space. This simplification results in only two operations being defined to achieve the functionality required.

Initial references are obtained via two operations provided in the ORB object interface, providing facilities to list and resolve initial object references. These are:

- `<bold>resolve_initial_references</bold>(String name)`
- `<bold>list_initial_services</bold>()`
- `<bold>register_initial_reference</bold>(String id, org.omg.CORBA.Object obj)`

An example that uses some of these methods is Getting Started with Java IDL.

## Exceptions

Exceptions in Java IDL are similar to those in any code written in the Java programming language. If a method is defined to throw an exception, then any code using that method must have a `try`/`catch` block and handle that exception when it is thrown.

The documentation on Java IDL exceptions has more information and explains the difference between system exceptions and user-defined exceptions.

The following is a list of the system exceptions (which are unchecked exceptions inheriting through `org.omg.CORBA.SystemException` from `java.lang.RuntimeException`) that are defined in the package `org.omg.CORBA`:

            BAD_CONTEXT
            BAD_INV_ORDER
            BAD_OPERATION
            BAD_PARAM
            BAD_TYPECODE
            COMM_FAILURE
            DATA_CONVERSION
            FREE_MEM
            IMP_LIMIT
            INITIALIZE
            INTERNAL
            INTF_REPOS
            INVALID_TRANSACTION
            INV_FLAG
            INV_IDENT
            INV_OBJREF
            INV_POLICY
            MARSHAL
            NO_IMPLEMENT
            NO_MEMORY
            NO_PERMISSION
            NO_RESOURCES
            NO_RESPONSE
            OBJECT_NOT_EXIST
            OBJ_ADAPTER
            PERSIST_STORE
            TRANSACTION_REQUIRED
            TRANSACTION_ROLLEDBACK
            TRANSIENT
            UNKNOWN

The following is a list of user-defined exceptions defined in the package `org.omg.CORBA`.

            Bounds
            UnknownUserException
            WrongTransaction
            PolicyError

## Subpackages

There are some packages inside the `CORBA` package with "Package" as part of their names. These packages are generally quite small because all they do is provide exceptions or classes for use by interfaces and classes in the `CORBA` package.

For example, the package `org.omg.CORBA.TypeCodePackage` contains two exceptions thrown by methods in the class `TypeCode`. These exceptions are:

- `BadKind`
- `Bounds`

The package `org.omg.CORBA.ORBPackage` contains two exceptions:

- `InvalidName`
- `InconsistentTypeCode`

Another package that is a subpackage of `CORBA` is the `portable` package. It provides a set of ORB APIs that makes it possible for code generated by one vendor's IDL compiler to run on another vendor's ORB.

## Holder classes

Support for out and inout parameter passing modes requires the use of additional holder classes. Because the Java programming language does not support out or inout parameters, holder classes are needed as a means of passing a parameter that can be modified. To support portable stubs and skeletons, holder classes also implement the `org.omg.CORBA.portable.Streamable` interface.

Holder classes are named by appending "Holder" to the name of the type. The name of the type refers to its name in the Java programming language. For example, a holder class for the interface named `Account` in the Java programming language would be named `AccountHolder`.

Holder classes are available for all of the basic IDL datatypes in the `org.omg.CORBA` package. So, for example, there are already-defined classes for `LongHolder`, `ShortHolder`, `FloatHolder`, and so on. Classes are also generated for all named user-defined IDL types except those defined by `typedefs`. (Note that in this context user defined includes types that are defined in OMG specifications such as those for the Interface Repository, and other OMG services.)

Each holder class has:

- a constructor from an instance
- a default constructor
- a public instance member, `value` which is the typed value.
- a method for reading an input stream and assigning the contents to the type's `value` field
- a method for writing the value of the `value` field to an output stream
- a method for getting the typecode of the type

The default constructor sets the value field to the default value for the type as defined by the Java language:

- `false` for boolean
- `0` for numeric and char types
- `null` for strings and object references

As an example, if the interface `Account`, defined in OMG IDL, were mapped to the Java programming language, the following holder class would be generated:

    public final class AccountHolder implements
        org.omg.CORBA.portable.Streamable
    {
      // field that holds an Account object
      public Account value = null;

      // default constructor
      public AccountHolder ()
      {
      }

      // creates a new AccountHolder from initialValue
      public AccountHolder (Account initialValue)
      {
        value = initialValue;
      }

      // reads the contents of i and assigns the contents to value
      public void _read (org.omg.CORBA.portable.InputStream i)
      {
        value = AccountHelper.read (i);
      }

      // writes value to o
      public void _write (org.omg.CORBA.portable.OutputStream o)
      {
        AccountHelper.write (o, value);
      }

      // returns the typecode for Account
      public org.omg.CORBA.TypeCode _type ()
      {
        return AccountHelper.type ();
      }

    }

For more information on Holder classes, see Chapter 1.4, Mapping for Basic Types in the OMG IDL to Java Language Mapping. The Holder classes defined in the package `org.omg.CORBA` are:

         AnyHolder
         AnySeqHolder
         BooleanHolder
         BooleanSeqHolder
         ByteHolder
         CharHolder
         CharSeqHolder
         CurrentHolder
         DoubleHolder
         DoubleSeqHolder
         FixedHolder
         FloatHolder
         FloatSeqHolder
         IntHolder
         LongHolder
         LongLongSeqHolder
         LongSeqHolder
         ObjectHolder
         OctetSeqHolder
         ParameterModeHolder
         PolicyErrorHolder
         PolicyListHolder
         PrincipalHolder
         ServiceInformationHolder
         ShortHolder
         ShortSeqHolder
         StringHolder
         StringSeqHolder
         TypeCodeHolder
         ULongLongSeqHolder
         ULongSeqHolder
         UnknownUserExceptionHolder
         UShortSeqHolder
         ValueBaseHolder
         WCharSeqHolder
         WrongTransactionHolder
         WStringSeqHolder

## Helper Classes

Helper files supply several static methods needed to manipulate the type. These include:

- `Any` insert and extract operations for the type
- getting the repository id
- getting the typecode
- reading and writing the type from and to a stream
- implement the `ValueHelper` interface (if it is a user-defined value type)

The helper class for a mapped IDL interface or abstract interface also include narrow operation(s). The static narrow method allows an `org.omg.CORBA.Object` to be narrowed to the object reference of a more specific type. The IDL exception `CORBA.BAD_PARAM` is thrown if the narrow fails because the object reference does not support the requested type. A different system exception is raised to indicate other kinds of errors. Trying to narrow a `null` will always succeed with a return value of `null`. Generally, the only helper method an application programmer uses is the `narrow` method. The other methods are normally used behind the scenes and are transparent to the programmer.

Helper classes fall into two broad categories, helpers for value types and helpers for non value types. Because all of the helper classes in one category provide the same methods, one generic explanation of each category of helper classes is presented here.

When OMG IDL is mapped to the Java programming language, a "helper" class is generated for each user-defined type. This generated class will have the name of the user-defined type with the suffix `Helper` appended. For example, if the interface `Account` is defined in OMG IDL, the `idlj` compiler will automatically generate a class named `AccountHelper`. The `AccountHelper` class will contain the static methods needed for manipulating instances of the type, in this case, `Account` objects.

### The `narrow` Method

When an object is the return value for a method, it is returned in the form of a generic object, either an `org.omg.CORBA.Object` object or a `java.lang.Object` object. This object must be cast to its more specific type before it can be operated on. For example, an `Account` object will be returned as a generic object and must be narrowed to an `Account` object so that `Account` methods may be called on it.

The `narrow` method has two forms, one that takes an `org.omg.CORBA.Object` object and one that takes a `java.lang.Object` object. Whether the interface is abstract or not determines which `narrow` method its helper class will provide. The helper class for an interface that is not abstract will have a `narrow` method that takes a CORBA object, whereas the `narrow` method for an interface that is abstract will take an object in the Java programming language. The helper class for a non-abstract interface that has at least one abstract base interface will provide both versions of the `narrow` method.

The Hello World tutorial uses a `narrow` method that looks like this:

            // create and initialize the ORB
    	ORB orb = ORB.init(args, null);

            // get the root naming context
            org.omg.CORBA.Object objRef =
    	    orb.resolve_initial_references("NameService");
            // Use NamingContextExt instead of NamingContext. This is
            // part of latest Inter-Operable naming Service.
            NamingContextExt ncRef = NamingContextExtHelper.narrow(objRef);

            // resolve the Object Reference in Naming
            String name = "Hello";
            helloImpl = HelloHelper.narrow(ncRef.resolve_str(name));

### Example of a Basic Helper Class

A basic helper class, for purposes of this explanation, is one with the methods that are provided by every helper class, plus a `narrow` method if the type defined in OMG IDL maps to an interface in the Java programming language. Types that are not value types will have a basic helper class generated for them.

For example, assuming that the interface `Account` is not a value type IDL type and is also not an abstract interface and has no abstract base interfaces, its `AccountHelper` class will look like this:

    abstract public class AccountHelper
    {
      private static String  _id = "IDL:Account:1.0";

      // inserts an Account object into an Any object
      public static void insert (org.omg.CORBA.Any a, Account that)
      {
        org.omg.CORBA.portable.OutputStream out = a.create_output_stream ();
        a.type (type ());
        write (out, that);
        a.read_value (out.create_input_stream (), type ());
      }

      // extracts an Account object from an Any object
      public static Account extract (org.omg.CORBA.Any a)
      {
        return read (a.create_input_stream ());
      }

      private static org.omg.CORBA.TypeCode __typeCode = null;
      // gets the typecode for this type
      synchronized public static org.omg.CORBA.TypeCode type ()
      {
        if (__typeCode == null)
        {
          __typeCode = org.omg.CORBA.ORB.init ().create_interface_tc (AccountHelper.id (), "Account");
        }
        return __typeCode;
      }

      // gets the repository id for this type
      public static String id ()
      {
        return _id;
      }

      // reads an Account object from an input stream
      public static Account read (org.omg.CORBA.portable.InputStream istream)
      {
        return narrow (istream.read_Object (_AccountStub.class));
      }

      // writes an Account object to an outputstream
      public static void write (org.omg.CORBA.portable.OutputStream ostream, Account value)
      {
        ostream.write_Object ((org.omg.CORBA.Object) value);
      }

      // converts (narrows) an Object to an Account object
      public static Account narrow (org.omg.CORBA.Object obj)
      {
        if (obj == null)
          return null;
        else if (obj instanceof Account)
          return (Account)obj;
        else if (!obj._is_a (id ()))
          throw new org.omg.CORBA.BAD_PARAM ();
        else
        {
          org.omg.CORBA.portable.Delegate delegate = ((org.omg.CORBA.portable.ObjectImpl)obj)._get_delegate ();
          _AccountStub stub = new _AccountStub ();
          stub._set_delegate(delegate);
          return stub;
        }
      }

    }

### Value Type Helper Classes

A helper class for a value type includes different renderings of the same methods generated for non-value type methods. The main difference is that value types are types that can be passed by value as parameters or return values of a method, which means that they must be serializable.

Assuming that `Address` is a value type, the `AddressHelper` class will look like this:

    abstract public class AddressHelper
    {
      private static String  _id = "IDL:Address:1.0";

      // same as for non-value type
      public static void insert (org.omg.CORBA.Any a, Address that)
      {
        org.omg.CORBA.portable.OutputStream out = a.create_output_stream ();
        a.type (type ());
        write (out, that);
        a.read_value (out.create_input_stream (), type ());
      }

      // same as for non-value type
      public static Address extract (org.omg.CORBA.Any a)
      {
        return read (a.create_input_stream ());
      }

      private static org.omg.CORBA.TypeCode __typeCode = null;
      private static boolean __active = false;

      // getting the typecode for the type
      synchronized public static org.omg.CORBA.TypeCode type ()
      {
        if (__typeCode == null)
        {
          synchronized (org.omg.CORBA.TypeCode.class)
          {
            if (__typeCode == null)
            {
              if (__active)
              {
                return org.omg.CORBA.ORB.init().create_recursive_tc ( _id );
              }
              __active = true;
              org.omg.CORBA.ValueMember[] _members0 = new org.omg.CORBA.ValueMember[0];
              org.omg.CORBA.TypeCode _tcOf_members0 = null;
              __typeCode = org.omg.CORBA.ORB.init ().create_value_tc (_id, "Address", org.omg.CORBA.VM_NONE.value, null, _members0);
              __active = false;
            }
          }
        }
        return __typeCode;
      }

      // same as for non-value type
      public static String id ()
      {
        return _id;
      }

      // reads a serializable instance of Address from the given input stream
      public static Address read (org.omg.CORBA.portable.InputStream istream)
      {
        return (Address)((org.omg.CORBA_2_3.portable.InputStream) istream).read_value (id ());
      }

      // writes a serializable instance of Address to the given output stream
      public static void write (org.omg.CORBA.portable.OutputStream ostream, Address value)
      {
        ((org.omg.CORBA_2_3.portable.OutputStream) ostream).write_value (value, id ());
      }

    }

The Helper classes defined in the package `org.omg.CORBA` are:

         AnySeqHelper
         BooleanSeqHelper
         CharSeqHelper
         CompletionStatusHelper
         CurrentHelper
         DefinitionKindHelper
         DoubleSeqHelper
         FieldNameHelper
         FloatSeqHelper
         IdentifierHelper
         IDLTypeHelper
         LongLongSeqHelper
         LongSeqHelper
         NameValuePairHelper
         ObjectHelper
         OctetSeqHelper
         ParameterModeHelper
         PolicyErrorCodeHelper
         PolicyErrorHelper
         PolicyHelper
         PolicyListHelper
         PolicyTypeHelper
         RepositoryIdHelper
         ServiceDetailHelper
         ServiceInformationHelper
         SetOverrideTypeHelper
         ShortSeqHelper
         StringSeqHelper
         StringValueHelper
         StructMemberHelper
         ULongLongSeqHelper
         ULongSeqHelper
         UnionMemberHelper
         UnknownUserExceptionHelper
         UShortSeqHelper
         ValueBaseHelper
         ValueMemberHelper
         VersionSpecHelper
         VisibilityHelper
         WCharSeqHelper
         WrongTransactionHelper
         WStringSeqHelper
         WStringValueHelper

# Other Classes

The other classes and interfaces in the `CORBA` package, which are used behind the scenes, can be put into four groups. Three of the groups are used with requests in some capacity, and the fourth group, concerning the Interface Repository, is a category by itself.

## Classes Created by an ORB

The first group contains classes that are created by an ORB and contain information used in request operations.

- `TCKind` -- indicates the kind (datatype) for a `TypeCode` object
- `TypeCode` -- indicates a datatype and possibly other information
- `Any` -- contains a value and its typecode
- `NamedValue` -- contains a name, an `Any` object, and an argument mode flag. `NamedValue` objects contain information about method arguments, method return values, or a context.
- `ContextList` -- a list of strings that describe the contexts that need to be resolved and sent with an invocation
- `ExceptionList` -- a list of `TypeCode`s for exceptions that may be thrown by a method
- `Environment` -- a container for the exception thrown during a method invocation
- `Context` -- a list of `NamedValue` objects used to pass auxiliary information from client to server
- `NVList` -- a list of `NamedValue` objects, used to pass arguments or get results

## Classes That Deal with Requests

The second group of classes deals with requests:

- `Object` -- the base class for all CORBA object references
- `Request` -- the main class in the DII, which contains methods for adding arguments to the request, for accessing information about the method being invoked (the method name, its arguments, exceptions it throws, and so on), and for making invocations on the request
- `DynamicImplementation` -- the base class for server implementations using the DSI. It has the method `invoke`, which is used by an implementation of this class to determine the state of a `ServerRequest` object and to set its result or exception
- `ServerRequest` -- captures the explicit state of a request for the Dynamic Skeleton Interface

## Interfaces That Serve as Constants

The third group contains interfaces that serve as constants. The IDL-to-Java mapping mandates that IDL enums are mapped to a Java class with the enumerated values represented as public static final fields in that class (e.g. DefinitionKind). On the other hand IDL constants defined outside of an IDL interface are mapped to a Java interface for each constant.

This is why several interfaces in the `org.omg.CORBA` package consist of a single field, `value`, which is a `short`. This field is a constant used for such things as an error code or value modifier. For example, the `value` field of the interface `BAD_POLICY` is one of the possible reasons for the exception `PolicyError` to be thrown. To specify this error code, you would use `BAD_POLICY.value`.

The exception `PolicyError` uses the `value` field of the following interfaces as its possible error codes.

- `BAD_POLICY`
- `BAD_POLICY_TYPE`
- `BAD_POLICY_VALUE`
- `UNSUPPORTED_POLICY`
- `UNSUPPORTED_POLICY_VALUE`

The method `TypeCode.type_modifier` returns the `value` field of one of the following interfaces. The `VM` in the names of these interfaces stands for "value modifier."

- `VM_NONE`
- `VM_ABSTRACT`
- `VM_CUSTOM`
- `VM_TRUNCATABLE`

The following constants are returned by a `ValueMember` object's access method to denote the visibility of the `ValueMember` object.

- `PRIVATE_MEMBER`
- `PUBLIC_MEMBER`

These flags, used in `NamedValue` objects or as parameters to methods, are defined in the following interfaces:

- `ARG_IN`
- `ARG_INOUT`
- `ARG_OUT`
- `CTX_RESTRICT_SCOPE`

## Interface Repository Interfaces and Classes

A fourth group contains the Interface Repository interfaces and classes, which are generated by the `idlj` compiler from the OMG IDL interface `ir.idl`. The purpose of the Interface Repository is to identify the interfaces stored in it so that they can be accessed by an ORB. Each module, type, interface, attribute, operation, parameter, exception, constant, and so on is described completely by the Interface Repository API.

An ORB does not require that there be an interface repository, and Java IDL does not include one. Even though this release does not include an implementation of an interface repository, the following IR classes and interfaces have been included for the purpose of creating typecodes (see create_value_tc, create_struct_tc, create_union_tc and create_exception_tc methods in interface org.omg.CORBA.ORB):
&nbs

- IRObject
- IDLType
- DefinitionKind
- StructMember
- UnionMember
- ValueMember

# Related Documentation

For overviews, guides, and a tutorial, please see:

- Java IDL home page

# CORBA Features Not Implemented in Java IDL

Some of the API included in `org.omg` subpackages is provided for conformance with the current OMG CORBA specification but is not implemented in Sun's release of the JDKTM. This enables other JDK licensees to provide implementations of this API in standard extensions and products.

## Features That Throw NO_IMPLEMENT

Some of the API included in `org.omg` subpackages throw `NO_IMPLEMENT` exceptions for various reasons. Among these reasons are:

- In some cases, for example `LocalObject`, the complete implementation according to the specification indicates that these API should throw `NO_IMPLEMENT`.

- In most cases, for example methods in `ORB.java`, methods that throw `NO_IMPLEMENT` are actually implemented in subclasses elsewhere in the ORB code.

- In some cases, for example `_get_interface_def()` and `_get_interface`, API are really not yet implemented.

## General Summary of Features or API Not Implemented in This Release:

- Interface Repository. An Interface Repository is not required for normal operation of Java IDL.
- Java IDL does not support `long double`.
- Policies (`org.omg.CORBA.Policy`) and methods for getting them are not implemented.
- Domain managers (`org.omg.CORBA.DomainManager`) and methods for getting them are not implemented.
- Service Information `org.omg.CORBA.ServiceInformation` and ORB method `public boolean get_service_information(short service_type, ServiceInformationHolder service_info)` are not implemented.
- ORB methods for supporting single-threading (`perform_work`, `work_pending`) are not implemented.
- IDL contexts.

## Specific List of Unimplemented Features in Package `org.omg.CORBA`

### Unimplemented Methods in package `org.omg.CORBA`:

- `ORB`
  - `public org.omg.CORBA.Policy create_policy(int type, org.omg.CORBA.Any val)`
  - `public void perform_work()`
  - `public boolean work_pending()`
  - `public org.omg.CORBA.Current get_current()`
  - `create_operation_list`
  - `get_default_context`
  - `get_service_information`
  - obsolete `DynAnys` (deprecated in favor of `DynamicAny` package)

@since JDK1.2 @serial exclude