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PART II The IDL And the Mapping to Java

• or
• A language which is not a programming language
  but used to develop programs.

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The OMG IDL - Overview

• The syntax of the IDL is largely drawn from C
  (but you don't need to know C to learn the IDL)
  .
• There are no programming statements, the only
  purpose is to define interface signatures.

3
The OMG IDL Overview.

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces and Modules
• and more ...

4
IDL Lexical Analysis

• The standard C preprocessing macros (include,
  define, ifdef, pragma) are available in IDL.
• Keywords are in lowercase.
• Comments are in C/Java style
• //, / ... /

5
IDL Modules and Interfaces

• To avoid name conflicts a module is used as a
  naming scope.
• Modules can contain any well formed IDL,
  including nested modules.
• An interface also opens a new naming scope and
  can contain constants, data type declarations,
  attributes, and operations.

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IDL Inheritance.

• IDL supports inheritance
• module InheritanceExample
• interface Fred
• string sayHi()
• interface Kurt Fred
• string sayGoodBye()

Also allowed Multiple Inheritance
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IDL Types and Constants

• The following basic types are available in IDL
• short, unsigned short, long, unsigned long, long
  long, unsigned long long, float, double, long
  double, fixed, char, wchar, boolean, string,
  wstring, octet, enum, any.
• Excercise How are all this types mapped into
  Java? C?

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IDL Types and Constants- Integer types

• unsigned short
• Signed unsigned 16-bit 2's complement integer
• unsigned long
• Signed unsigned 32-bit 2's complement integer
• unsigned long long
• Signed unsigned 64-bit 2's complement integer

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IDL Types and Constants- Floating point types

• float
• 16-bit IEEE floating point number
• double
• 32-bit IEEE floating point number
• long double
• 64-bit IEEE floating point number

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IDL Types and Constants- Fixed point type

• fixed
• fixed-point decimal number of up to 31 digits.
• Fixed-point types are template types and need to
  be introduced via typedef
• typedef fixedlt5,2gt priceTag
• declares a fixed point type priceTag with 3
  digits before and two digits behind the point,
  e.g. 123.45

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IDL Types and Constants- characters

• char
• ISO Latin-1 character
• wchar
• character from other character sets to support
  internationalisation. The size is implementation
  dependent.

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IDL Types and Constants- strings

• string
• Variable-length string of characters whose length
  is available at run time.
• wstring
• Variable-length string of wchar characters.
• Strings may be bounded or unbounded, e.g. typedef
  stringlt8gt eightLetters for a bounded string of 8
  characters.

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IDL Types and Constants- miscellaneous

• boolean
• TRUE or FALSE
• octet
• 8-bit uninterpreted type
• enum
• Enumerated type with named integer values.

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IDL Types and Constants- miscellaneous

• any
• Can represent a value from any possible IDL type,
  basic or constructed, object or nonobject. any
  has an application interface describing how
  values are inserted, extracted, and how the type
  can be discovered.

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IDL other constructs

• Arrays (similar to Java, C, ...)
• Sequences (a more flexible version of arrays)
• Exceptions, Constants, Structs Unions.

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IDL Operations Attributes

• As seen in the example operations are similar
  to C function prototypes
• They contain a name, return type, and the
  parameter list.
• An Attribute is logically equivalent to a pair of
  accessor/modifier operations.
• No "private" part!

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IDL - Operations

• CORBA specific extensions
• one-way operations
• in, out and inout parameters
• and others

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The IDL to Java mapping

• or
• How to translate an IDL to a language where you
  can really write programs.

http//www.omg.org/technology/documents/idl2x_spec
_catalog.htm
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Mapping IDL to Java

• The IDL compiler (e.g. idlj) translates an IDL to
  a set of Java classes.
• That means that each IDL construct is mapped to a
  Java construct.

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Mapping IDL to Java

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces
• Modules

• IDL Attributes are mapped to a pair of accessor
  and modifier methods in Java.
• Note IDL Attributes are not mapped to private
  attributes.

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Mapping IDL to Java

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces
• Modules

• IDL operations are mapped to Java methods as seen
  in the HelloWorld example.

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Mapping IDL to Java

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces
• Modules

• Interfaces are mapped to Java interfaces/classes
  as seen in the example.
• Note One interface generates more then one Java
  class/interface (Helper classes, )

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Mapping IDL to Java

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces
• Modules

• Modules are mapped to Java package names.
• Each module generates a directory in which other
  modules ore classes/interfaces can be found.

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Mapping IDL to Java

• IDL supports the following constructs
• Data type declarations
• Attributes
• Operations
• Interfaces
• Modules

• Basic data types are mapped as good as possible
  to matching basic data types or classes of Java.
• More details on next slides

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IDL Types and Constants

• This is the complete list of the basic types
  available in IDL
• short, unsigned short, long, unsigned long, long
  long, unsigned long long, float, double, long
  double, fixed, char, wchar, boolean, string,
  wstring, octet, enum, any.
• The blue ones do also exist in Java. What about
  the others?

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IDL Java mapping- Signed integer types

• short (16 bit)
• Mapped to Java short.
• long (32 bit)
• Mapped to Java int
• long long (64 bit)
• Mapped to Java long

• Caveat!
• The CORBA type long and the Java type long are
  different!

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IDL Java Mapping- Unsigned integer types

• There is an obvious type mismatch here.
• However, the mapping is defined from unsigned
  CORBA types to signed Java types.

• unsigned short (16 bit)
• Mapped to Java short.
• unsigned long (32 bit)
• Mapped to Java int
• unsigned long long (64 bit)
• Mapped to Java long

Is this a problem? Why? Why not?
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IDL Types and Constants- Floating point types

• float
• 16-bit IEEE floating point number
• mapped to the Java type float
• double
• 32-bit IEEE floating point number
• mapped to the Java type double
• long double
• 64-bit IEEE floating point number
• so far not mapped!

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IDL to Java mapping- Fixed point type

• fixed
• fixed-point deximal number of up to 31 digits,
  e.g.
• typedef fixedlt5,2gt priceTag
• The IDL type fixed is mapped to the Java class
  java.math.BigDecimal.
• Range checking is performed at run time.
• Exceptions are raised if values are outside of
  the range.

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IDL to Java mapping- characters

• char, wchar
• are both mapped to the Java type char.
• Note IDL char is 8-bit, IDL wchar is 16-bit, the
  Java char is 16-bit.
• Also The IDL wchar can hold characters which are
  not part of Javas native Unicode set (possible
  problems with non-European character sets
  possible C/Java incompatibilities).

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IDL Types and Constants- strings

• string
• Variable-length string of characters whose length
  is available at run time.
• wstring
• Variable-length string of wchar characters.
• Strings may be bounded or unbounded, e.g.
  typedef stringlt8gt eightLetters for a bounded
  string of 8 characters.

• These are mapped to java.lang.String with
  possible exceptions raised for bounded strings.

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IDL Types and Constants- miscellaneous

• boolean (TRUE or FALSE)
• mapped to the Java type boolean.
• octet (8-bit uninterpreted type)
• mapped to the Java type byte.
• enum (enumerated type with named integer values.)
• mapped to a final Java class emulating the
  required properties. (Maybe different in future
  because of Java 1.5 supporting enum type)

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IDL mapping of any

• any (Can represent a value from any possible IDL
  type, basic or constructed, object or nonobject.
  any has an application interface describing how
  values are inserted, extracted, and how the type
  can be discovered.)
• mapped to org.omg.CORBA.any

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Summary

• Overview of the IDL (Examples)
• Overview on how the IDL is mapped to Java
  (Examples)