Module java.corba
Package org.omg.CORBA

Class ORB

  • Direct Known Subclasses:
    ORB

    public abstract class ORB
extends Object
    A class providing APIs for the CORBA Object Request Broker features. The ORB class also provides "pluggable ORB implementation" APIs that allow another vendor's ORB implementation to be used.

    An ORB makes it possible for CORBA objects to communicate with each other by connecting objects making requests (clients) with objects servicing requests (servers).

    The ORB class, which encapsulates generic CORBA functionality, does the following: (Note that items 5 and 6, which include most of the methods in the class ORB, are typically used with the Dynamic Invocation Interface (DII) and the Dynamic Skeleton Interface (DSI). These interfaces may be used by a developer directly, but most commonly they are used by the ORB internally and are not seen by the general programmer.)

    1. initializes the ORB implementation by supplying values for predefined properties and environmental parameters
    2. obtains initial object references to services such as the NameService using the method resolve_initial_references
    3. converts object references to strings and back
    4. connects the ORB to a servant (an instance of a CORBA object implementation) and disconnects the ORB from a servant
    5. creates objects such as
      • TypeCode
      • Any
      • NamedValue
      • Context
      • Environment
      • lists (such as NVList) containing these objects
    6. sends multiple messages in the DII

    The ORB class can be used to obtain references to objects implemented anywhere on the network.

    An application or applet gains access to the CORBA environment by initializing itself into an ORB using one of three init methods. Two of the three methods use the properties (associations of a name with a value) shown in the table below.

    Standard Java CORBA Properties:
    Property Name Property Value
    org.omg.CORBA.ORBClass class name of an ORB implementation
    org.omg.CORBA.ORBSingletonClass class name of the ORB returned by init()

    These properties allow a different vendor's ORB implementation to be "plugged in."

    When an ORB instance is being created, the class name of the ORB implementation is located using the following standard search order:

    1. check in Applet parameter or application string array, if any
    2. check in properties parameter, if any
    3. check in the System properties, if any
    4. check in the orb.properties file located in the user.home directory, if any
    5. check in the orb.properties file located in the run-time image, if any
    6. fall back on a hardcoded default behavior (use the Java IDL implementation)

    Note that Java IDL provides a default implementation for the fully-functional ORB and for the Singleton ORB. When the method init is given no parameters, the default Singleton ORB is returned. When the method init is given parameters but no ORB class is specified, the Java IDL ORB implementation is returned.

    The following code fragment creates an ORB object initialized with the default ORB Singleton. This ORB has a restricted implementation to prevent malicious applets from doing anything beyond creating typecodes. It is called a singleton because there is only one instance for an entire virtual machine. 

        ORB orb = ORB.init();

    The following code fragment creates an ORB object for an application. The parameter args represents the arguments supplied to the application's main method. Since the property specifies the ORB class to be "SomeORBImplementation", the new ORB will be initialized with that ORB implementation. If p had been null, and the arguments had not specified an ORB class, the new ORB would have been initialized with the default Java IDL implementation. 

        Properties p = new Properties();
    p.put("org.omg.CORBA.ORBClass", "SomeORBImplementation");
    ORB orb = ORB.init(args, p);

    The following code fragment creates an ORB object for the applet supplied as the first parameter. If the given applet does not specify an ORB class, the new ORB will be initialized with the default Java IDL implementation. 

        ORB orb = ORB.init(myApplet, null);

    An application or applet can be initialized in one or more ORBs. ORB initialization is a bootstrap call into the CORBA world.

    Implementation Note:
    When a singleton ORB is configured via the system property, or orb.properties, it will be located, and loaded via the system class loader. Thus, where appropriate, it is necessary that the classes for this alternative ORBSingleton are available on the application's class path. It should be noted that the singleton ORB is system wide.

    When a per-application ORB is created via the 2-arg init methods, then it will be located using the thread context class loader.

    The IDL to Java Language OMG specification documents the ${java.home}/lib directory as the location, in the Java run-time image, to search for orb.properties. This location is not intended for user editable configuration files. Therefore, the implementation first checks the ${java.home}/conf directory for orb.properties, and thereafter the ${java.home}/lib directory.

    See also IDL developer's guide.

    Since:
    JDK1.2

    • Constructor Detail

      • ORB

        public ORB​()

    • Method Detail

      • init

        public static ORB init​()
        Returns the ORB singleton object. This method always returns the same ORB instance, which is an instance of the class described by the org.omg.CORBA.ORBSingletonClass system property.

        This no-argument version of the method init is used primarily as a factory for TypeCode objects, which are used by Helper classes to implement the method type. It is also used to create Any objects that are used to describe union labels (as part of creating a TypeCode object for a union).

        This method is not intended to be used by applets, and in the event that it is called in an applet environment, the ORB it returns is restricted so that it can be used only as a factory for TypeCode objects. Any TypeCode objects it produces can be safely shared among untrusted applets.

        If an ORB is created using this method from an applet, a system exception will be thrown if methods other than those for creating TypeCode objects are invoked.

        Implementation Note:
        When configured via the system property, or orb.properties, the system-wide singleton ORB is located via the system class loader.
        Returns:
        the singleton ORB

      • init

        public static ORB init​(String[] args,
                       Properties props)
        Creates a new ORB instance for a standalone application. This method may be called from applications only and returns a new fully functional ORB object each time it is called.
        Implementation Note:
        When configured via the system property, or orb.properties, the ORB is located via the thread context class loader.
        Parameters:
        args - command-line arguments for the application's main method; may be null
        props - application-specific properties; may be null
        Returns:
        the newly-created ORB instance

      • init

        public static ORB init​(Applet app,
                       Properties props)
        Creates a new ORB instance for an applet. This method may be called from applets only and returns a new fully-functional ORB object each time it is called.
        Implementation Note:
        When configured via the system property, or orb.properties, the ORB is located via the thread context class loader.
        Parameters:
        app - the applet; may be null
        props - applet-specific properties; may be null
        Returns:
        the newly-created ORB instance

      • set_parameters

        protected abstract void set_parameters​(String[] args,
                                       Properties props)
        Allows the ORB implementation to be initialized with the given parameters and properties. This method, used in applications only, is implemented by subclass ORB implementations and called by the appropriate init method to pass in its parameters.
        Parameters:
        args - command-line arguments for the application's main method; may be null
        props - application-specific properties; may be null

      • set_parameters

        protected abstract void set_parameters​(Applet app,
                                       Properties props)
        Allows the ORB implementation to be initialized with the given applet and parameters. This method, used in applets only, is implemented by subclass ORB implementations and called by the appropriate init method to pass in its parameters.
        Parameters:
        app - the applet; may be null
        props - applet-specific properties; may be null

      • connect

        public void connect​(Object obj)
        Connects the given servant object (a Java object that is an instance of the server implementation class) to the ORB. The servant class must extend the ImplBase class corresponding to the interface that is supported by the server. The servant must thus be a CORBA object reference, and inherit from org.omg.CORBA.Object. Servants created by the user can start receiving remote invocations after the method connect has been called. A servant may also be automatically and implicitly connected to the ORB if it is passed as an IDL parameter in an IDL method invocation on a non-local object, that is, if the servant object has to be marshalled and sent outside of the process address space.

        Calling the method connect has no effect when the servant object is already connected to the ORB.

        Deprecated by the OMG in favor of the Portable Object Adapter APIs.

        Parameters:
        obj - The servant object reference

      • destroy

        public void destroy​()
        Destroys the ORB so that its resources can be reclaimed. Any operation invoked on a destroyed ORB reference will throw the OBJECT_NOT_EXIST exception. Once an ORB has been destroyed, another call to init with the same ORBid will return a reference to a newly constructed ORB.

        If destroy is called on an ORB that has not been shut down, it will start the shut down process and block until the ORB has shut down before it destroys the ORB.
        If an application calls destroy in a thread that is currently servicing an invocation, the BAD_INV_ORDER system exception will be thrown with the OMG minor code 3, since blocking would result in a deadlock.

        For maximum portability and to avoid resource leaks, an application should always call shutdown and destroy on all ORB instances before exiting.

        Throws:
        BAD_INV_ORDER - if the current thread is servicing an invocation

      • disconnect

        public void disconnect​(Object obj)
        Disconnects the given servant object from the ORB. After this method returns, the ORB will reject incoming remote requests for the disconnected servant and will send the exception org.omg.CORBA.OBJECT_NOT_EXIST back to the remote client. Thus the object appears to be destroyed from the point of view of remote clients. Note, however, that local requests issued using the servant directly do not pass through the ORB; hence, they will continue to be processed by the servant.

        Calling the method disconnect has no effect if the servant is not connected to the ORB.

        Deprecated by the OMG in favor of the Portable Object Adapter APIs.

        Parameters:
        obj - The servant object to be disconnected from the ORB

      • list_initial_services

        public abstract String[] list_initial_services​()
        Returns a list of the initially available CORBA object references, such as "NameService" and "InterfaceRepository".
        Returns:
        an array of String objects that represent the object references for CORBA services that are initially available with this ORB

      • resolve_initial_references

        public abstract Object resolve_initial_references​(String object_name)
                                           throws InvalidName
        Resolves a specific object reference from the set of available initial service names.
        Parameters:
        object_name - the name of the initial service as a string
        Returns:
        the object reference associated with the given name
        Throws:
        InvalidName - if the given name is not associated with a known service

      • object_to_string

        public abstract String object_to_string​(Object obj)
        Converts the given CORBA object reference to a string. Note that the format of this string is predefined by IIOP, allowing strings generated by a different ORB to be converted back into an object reference.

        The resulting String object may be stored or communicated in any way that a String object can be manipulated.

        Parameters:
        obj - the object reference to stringify
        Returns:
        the string representing the object reference

      • string_to_object

        public abstract Object string_to_object​(String str)
        Converts a string produced by the method object_to_string back to a CORBA object reference.
        Parameters:
        str - the string to be converted back to an object reference. It must be the result of converting an object reference to a string using the method object_to_string.
        Returns:
        the object reference

      • create_list

        public abstract NVList create_list​(int count)
        Allocates an NVList with (probably) enough space for the specified number of NamedValue objects. Note that the specified size is only a hint to help with storage allocation and does not imply the maximum size of the list.
        Parameters:
        count - suggested number of NamedValue objects for which to allocate space
        Returns:
        the newly-created NVList
        See Also:
        NVList

      • create_operation_list

        public NVList create_operation_list​(Object oper)
        Creates an NVList initialized with argument descriptions for the operation described in the given OperationDef object. This OperationDef object is obtained from an Interface Repository. The arguments in the returned NVList object are in the same order as in the original IDL operation definition, which makes it possible for the list to be used in dynamic invocation requests.
        Parameters:
        oper - the OperationDef object to use to create the list
        Returns:
        a newly-created NVList object containing descriptions of the arguments to the method described in the given OperationDef object
        See Also:
        NVList

      • create_named_value

        public abstract NamedValue create_named_value​(String s,
                                              Any any,
                                              int flags)
        Creates a NamedValue object using the given name, value, and argument mode flags.

        A NamedValue object serves as (1) a parameter or return value or (2) a context property. It may be used by itself or as an element in an NVList object.

        Parameters:
        s - the name of the NamedValue object
        any - the Any value to be inserted into the NamedValue object
        flags - the argument mode flags for the NamedValue: one of ARG_IN.value, ARG_OUT.value, or ARG_INOUT.value.
        Returns:
        the newly-created NamedValue object
        See Also:
        NamedValue

      • create_exception_list

        public abstract ExceptionList create_exception_list​()
        Creates an empty ExceptionList object.
        Returns:
        the newly-created ExceptionList object

      • create_context_list

        public abstract ContextList create_context_list​()
        Creates an empty ContextList object.
        Returns:
        the newly-created ContextList object
        See Also:
        ContextList, Context

      • get_default_context

        public abstract Context get_default_context​()
        Gets the default Context object.
        Returns:
        the default Context object
        See Also:
        Context

      • create_environment

        public abstract Environment create_environment​()
        Creates an Environment object.
        Returns:
        the newly-created Environment object
        See Also:
        Environment

      • create_output_stream

        public abstract OutputStream create_output_stream​()
        Creates a new org.omg.CORBA.portable.OutputStream into which IDL method parameters can be marshalled during method invocation.
        Returns:
        the newly-created org.omg.CORBA.portable.OutputStream object

      • send_multiple_requests_oneway

        public abstract void send_multiple_requests_oneway​(Request[] req)
        Sends multiple dynamic (DII) requests asynchronously without expecting any responses. Note that oneway invocations are not guaranteed to reach the server.
        Parameters:
        req - an array of request objects

      • send_multiple_requests_deferred

        public abstract void send_multiple_requests_deferred​(Request[] req)
        Sends multiple dynamic (DII) requests asynchronously.
        Parameters:
        req - an array of Request objects

      • poll_next_response

        public abstract boolean poll_next_response​()
        Finds out if any of the deferred (asynchronous) invocations have a response yet.
        Returns:
        true if there is a response available; false otherwise

      • get_next_response

        public abstract Request get_next_response​()
                                   throws WrongTransaction
        Gets the next Request instance for which a response has been received.
        Returns:
        the next Request object ready with a response
        Throws:
        WrongTransaction - if the method get_next_response is called from a transaction scope different from the one from which the original request was sent. See the OMG Transaction Service specification for details.

      • get_primitive_tc

        public abstract TypeCode get_primitive_tc​(TCKind tcKind)
        Retrieves the TypeCode object that represents the given primitive IDL type.
        Parameters:
        tcKind - the TCKind instance corresponding to the desired primitive type
        Returns:
        the requested TypeCode object

      • create_struct_tc

        public abstract TypeCode create_struct_tc​(String id,
                                          String name,
                                          StructMember[] members)
        Creates a TypeCode object representing an IDL struct. The TypeCode object is initialized with the given id, name, and members.
        Parameters:
        id - the repository id for the struct
        name - the name of the struct
        members - an array describing the members of the struct
        Returns:
        a newly-created TypeCode object describing an IDL struct

      • create_union_tc

        public abstract TypeCode create_union_tc​(String id,
                                         String name,
                                         TypeCode discriminator_type,
                                         UnionMember[] members)
        Creates a TypeCode object representing an IDL union. The TypeCode object is initialized with the given id, name, discriminator type, and members.
        Parameters:
        id - the repository id of the union
        name - the name of the union
        discriminator_type - the type of the union discriminator
        members - an array describing the members of the union
        Returns:
        a newly-created TypeCode object describing an IDL union

      • create_enum_tc

        public abstract TypeCode create_enum_tc​(String id,
                                        String name,
                                        String[] members)
        Creates a TypeCode object representing an IDL enum. The TypeCode object is initialized with the given id, name, and members.
        Parameters:
        id - the repository id for the enum
        name - the name for the enum
        members - an array describing the members of the enum
        Returns:
        a newly-created TypeCode object describing an IDL enum

      • create_alias_tc

        public abstract TypeCode create_alias_tc​(String id,
                                         String name,
                                         TypeCode original_type)
        Creates a TypeCode object representing an IDL alias (typedef). The TypeCode object is initialized with the given id, name, and original type.
        Parameters:
        id - the repository id for the alias
        name - the name for the alias
        original_type - the TypeCode object describing the original type for which this is an alias
        Returns:
        a newly-created TypeCode object describing an IDL alias

      • create_exception_tc

        public abstract TypeCode create_exception_tc​(String id,
                                             String name,
                                             StructMember[] members)
        Creates a TypeCode object representing an IDL exception. The TypeCode object is initialized with the given id, name, and members.
        Parameters:
        id - the repository id for the exception
        name - the name for the exception
        members - an array describing the members of the exception
        Returns:
        a newly-created TypeCode object describing an IDL exception

      • create_interface_tc

        public abstract TypeCode create_interface_tc​(String id,
                                             String name)
        Creates a TypeCode object representing an IDL interface. The TypeCode object is initialized with the given id and name.
        Parameters:
        id - the repository id for the interface
        name - the name for the interface
        Returns:
        a newly-created TypeCode object describing an IDL interface

      • create_string_tc

        public abstract TypeCode create_string_tc​(int bound)
        Creates a TypeCode object representing a bounded IDL string. The TypeCode object is initialized with the given bound, which represents the maximum length of the string. Zero indicates that the string described by this type code is unbounded.
        Parameters:
        bound - the bound for the string; cannot be negative
        Returns:
        a newly-created TypeCode object describing a bounded IDL string
        Throws:
        BAD_PARAM - if bound is a negative value

      • create_wstring_tc

        public abstract TypeCode create_wstring_tc​(int bound)
        Creates a TypeCode object representing a bounded IDL wstring (wide string). The TypeCode object is initialized with the given bound, which represents the maximum length of the wide string. Zero indicates that the string described by this type code is unbounded.
        Parameters:
        bound - the bound for the wstring; cannot be negative
        Returns:
        a newly-created TypeCode object describing a bounded IDL wstring
        Throws:
        BAD_PARAM - if bound is a negative value

      • create_sequence_tc

        public abstract TypeCode create_sequence_tc​(int bound,
                                            TypeCode element_type)
        Creates a TypeCode object representing an IDL sequence. The TypeCode object is initialized with the given bound and element type.
        Parameters:
        bound - the bound for the sequence, 0 if unbounded
        element_type - the TypeCode object describing the elements contained in the sequence
        Returns:
        a newly-created TypeCode object describing an IDL sequence

      • create_recursive_sequence_tc

        @Deprecated
public abstract TypeCode create_recursive_sequence_tc​(int bound,
                                                      int offset)
        Deprecated. Use a combination of create_recursive_tc and create_sequence_tc instead
        Creates a TypeCode object representing a a recursive IDL sequence.

        For the IDL struct Node in following code fragment, the offset parameter for creating its sequence would be 1: 

            Struct Node {
        long value;
        Sequence <Node> subnodes;
    };
        Parameters:
        bound - the bound for the sequence, 0 if unbounded
        offset - the index to the enclosing TypeCode object that describes the elements of this sequence
        Returns:
        a newly-created TypeCode object describing a recursive sequence
        See Also:
        create_recursive_tc, create_sequence_tc

      • create_array_tc

        public abstract TypeCode create_array_tc​(int length,
                                         TypeCode element_type)
        Creates a TypeCode object representing an IDL array. The TypeCode object is initialized with the given length and element type.
        Parameters:
        length - the length of the array
        element_type - a TypeCode object describing the type of element contained in the array
        Returns:
        a newly-created TypeCode object describing an IDL array

      • create_native_tc

        public TypeCode create_native_tc​(String id,
                                 String name)
        Create a TypeCode object for an IDL native type.
        Parameters:
        id - the logical id for the native type.
        name - the name of the native type.
        Returns:
        the requested TypeCode.

      • create_abstract_interface_tc

        public TypeCode create_abstract_interface_tc​(String id,
                                             String name)
        Create a TypeCode object for an IDL abstract interface.
        Parameters:
        id - the logical id for the abstract interface type.
        name - the name of the abstract interface type.
        Returns:
        the requested TypeCode.

      • create_fixed_tc

        public TypeCode create_fixed_tc​(short digits,
                                short scale)
        Create a TypeCode object for an IDL fixed type.
        Parameters:
        digits - specifies the total number of decimal digits in the number and must be from 1 to 31 inclusive.
        scale - specifies the position of the decimal point.
        Returns:
        the requested TypeCode.

      • create_value_tc

        public TypeCode create_value_tc​(String id,
                                String name,
                                short type_modifier,
                                TypeCode concrete_base,
                                ValueMember[] members)
        Create a TypeCode object for an IDL value type. The concrete_base parameter is the TypeCode for the immediate concrete valuetype base of the valuetype for which the TypeCode is being created. It may be null if the valuetype does not have a concrete base.
        Parameters:
        id - the logical id for the value type.
        name - the name of the value type.
        type_modifier - one of the value type modifier constants: VM_NONE, VM_CUSTOM, VM_ABSTRACT or VM_TRUNCATABLE
        concrete_base - a TypeCode object describing the concrete valuetype base
        members - an array containing the members of the value type
        Returns:
        the requested TypeCode

      • create_recursive_tc

        public TypeCode create_recursive_tc​(String id)
        Create a recursive TypeCode object which serves as a placeholder for a concrete TypeCode during the process of creating TypeCodes which contain recursion. The id parameter specifies the repository id of the type for which the recursive TypeCode is serving as a placeholder. Once the recursive TypeCode has been properly embedded in the enclosing TypeCode which corresponds to the specified repository id, it will function as a normal TypeCode. Invoking operations on the recursive TypeCode before it has been embedded in the enclosing TypeCode will result in a BAD_TYPECODE exception.

        For example, the following IDL type declaration contains recursion: 

            Struct Node {
        Sequence<Node> subnodes;
    };

        To create a TypeCode for struct Node, you would invoke the TypeCode creation operations as shown below: 

         String nodeID = "IDL:Node:1.0";
 TypeCode recursiveSeqTC = orb.create_sequence_tc(0, orb.create_recursive_tc(nodeID));
 StructMember[] members = { new StructMember("subnodes", recursiveSeqTC, null) };
 TypeCode structNodeTC = orb.create_struct_tc(nodeID, "Node", members);

        Also note that the following is an illegal IDL type declaration: 

            Struct Node {
        Node next;
    };

        Recursive types can only appear within sequences which can be empty. That way marshaling problems, when transmitting the struct in an Any, are avoided.

        Parameters:
        id - the logical id of the referenced type
        Returns:
        the requested TypeCode

      • create_value_box_tc

        public TypeCode create_value_box_tc​(String id,
                                    String name,
                                    TypeCode boxed_type)
        Creates a TypeCode object for an IDL value box.
        Parameters:
        id - the logical id for the value type
        name - the name of the value type
        boxed_type - the TypeCode for the type
        Returns:
        the requested TypeCode

      • create_any

        public abstract Any create_any​()
        Creates an IDL Any object initialized to contain a Typecode object whose kind field is set to TCKind.tc_null.
        Returns:
        a newly-created Any object

      • get_current

        @Deprecated
public Current get_current​()
        Deprecated. use resolve_initial_references.
        Retrieves a Current object. The Current interface is used to manage thread-specific information for use by services such as transactions and security.
        Returns:
        a newly-created Current object
        See Also:
        CORBA package comments for unimplemented features

      • run

        public void run​()
        This operation blocks the current thread until the ORB has completed the shutdown process, initiated when some thread calls shutdown. It may be used by multiple threads which get all notified when the ORB shuts down.

      • shutdown

        public void shutdown​(boolean wait_for_completion)
        Instructs the ORB to shut down, which causes all object adapters to shut down, in preparation for destruction.
        If the wait_for_completion parameter is true, this operation blocks until all ORB processing (including processing of currently executing requests, object deactivation, and other object adapter operations) has completed. If an application does this in a thread that is currently servicing an invocation, the BAD_INV_ORDER system exception will be thrown with the OMG minor code 3, since blocking would result in a deadlock.
        If the wait_for_completion parameter is FALSE, then shutdown may not have completed upon return.

        While the ORB is in the process of shutting down, the ORB operates as normal, servicing incoming and outgoing requests until all requests have been completed. Once an ORB has shutdown, only object reference management operations may be invoked on the ORB or any object reference obtained from it. An application may also invoke the destroy operation on the ORB itself. Invoking any other operation will throw the BAD_INV_ORDER system exception with the OMG minor code 4.

        The ORB.run method will return after shutdown has been called.

        Parameters:
        wait_for_completion - true if the call should block until the shutdown is complete; false if it should return immediately
        Throws:
        BAD_INV_ORDER - if the current thread is servicing an invocation

      • work_pending

        public boolean work_pending​()
        Returns true if the ORB needs the main thread to perform some work, and false if the ORB does not need the main thread.
        Returns:
        true if there is work pending, meaning that the ORB needs the main thread to perform some work; false if there is no work pending and thus the ORB does not need the main thread

      • perform_work

        public void perform_work​()
        Performs an implementation-dependent unit of work if called by the main thread. Otherwise it does nothing. The methods work_pending and perform_work can be used in conjunction to implement a simple polling loop that multiplexes the main thread among the ORB and other activities.

      • get_service_information

        public boolean get_service_information​(short service_type,
                                       ServiceInformationHolder service_info)
        Used to obtain information about CORBA facilities and services that are supported by this ORB. The service type for which information is being requested is passed in as the in parameter service_type, the values defined by constants in the CORBA module. If service information is available for that type, that is returned in the out parameter service_info, and the operation returns the value true. If no information for the requested services type is available, the operation returns false (i.e., the service is not supported by this ORB).
        Parameters:
        service_type - a short indicating the service type for which information is being requested
        service_info - a ServiceInformationHolder object that will hold the ServiceInformation object produced by this method
        Returns:
        true if service information is available for the service_type; false if no information for the requested services type is available
        See Also:
        CORBA package comments for unimplemented features

      • create_policy

        public Policy create_policy​(int type,
                            Any val)
                     throws PolicyError
        Can be invoked to create new instances of policy objects of a specific type with specified initial state. If create_policy fails to instantiate a new Policy object due to its inability to interpret the requested type and content of the policy, it raises the PolicyError exception with the appropriate reason.
        Parameters:
        type - the PolicyType of the policy object to be created
        val - the value that will be used to set the initial state of the Policy object that is created
        Returns:
        Reference to a newly created Policy object of type specified by the type parameter and initialized to a state specified by the val parameter
        Throws:
        PolicyError - when the requested policy is not supported or a requested initial state for the policy is not supported.