Saturday February 14, 2004 10:29:28 ق.ظ

مقدمه ای بر زبان ادا به زبان اصلی

1. Ada (1979) : Ada, a very powerful, complex language, was developed by the Department of Defense for general purpose programming. Its sophisticated control structures and data structures also make it ideal for embedded applications (e.g. weapons systems) and real-time applications. Ada 95 is a superset of Ada that incorporates OOP features.
2. C (1974)and C++: C, developed for writing system software, is a "mid-level language" in that it has AL features and is more machine-oriented than HLL. Thus it can run faster than typical HLL and is an alternative to hard-to-develop, CPU-specific assembly languages. It was very popular with professional software developers, but has now been virtually replaced by C++, an extension of the language that provides OOP facilities, thus producing a "hybrid language". Both C and C++ code can be very cryptic and hard to understand.
3. Logo (1968, 1976): Logo was developed at MIT, as a "user-friendly version of LISP, to facilitate learning math concepts. It has become the language of choice for introducing programming, via "turtle graphics", to elementary school children. However its huge success at this has led to its underestimation as a language for other applications; in fact, many believed it is the most underrated of all programming languages. It is billed as a "complete learning environment" where exploration is the guiding principle.
4. PROLOG (1970): Based firmly on the principles of logic, it rivals LISP as the language of choice for AI programming. It has been chosen as the basic language for the "Fifth Generation of Computers" being built by the Japanese.
5. HyperTalk(1987): Hypertalkis a VHLL contained within "Hypercard", Apple's object oriented programming environment that is called " a soft-ware erector set for non programmers" . Hypertalk is Apple's implementation of Hypermedia, a VHLL language concept for handling information in all forms (data, text, graphics, animation, audio, and video). It is billed as the "language for the rest of us" in that it can be used by nonprogrammers to unleash the power of the computer.
6. Smalltalk (1974-1980): Smalltalk was the first purely object-oriented programming (OOP) language; it extends the ideas of structured programming to more human oriented viewpoints involving objects which respond to messages sent to them by the computer system under the direction of the user. Many say that Smalltalk is the prototype of the programming paradigm of the future, OOP.
7. Java (1991-today): Java is a purely OO, procedural, HLL designed to facilitate reliable, platform-independent, distributed processing. It has become "the" development language for Internet and intranet applications because Java "applets" (special programs) can be called directly from HTML.
   1. Java is the heart of the revolutionary NC (network computer).
   2. The reliability goal means it was designed to be secure (hacker resistant) and robust (bug resistant); its platform-independence means it is independent of the CPU and OS on which it is used.
8. JavaScript is VHLL that is a simplified version of Java specifically designed to add dynamic quality to Web pages; see HTML, below.
9. Hypertext Markup Language (HTML) is the VHLL used to create Web pages. It is really only a collection of tags which, when incerted into regular text, tell a Web browser how to:
   1. format text,
   2. incert an image, video clip, or sound into a Web page,
   3. link to another location in the page or another Web page, even on another computer (server) or
   4. link to other programs written in VRML, TVML, Java, JavaScript, or other languages.

  Object oriented programming languages allows software developers to construct programs as if they are collections of self-contained "components".  The fundamental component is the class which is a template from which actual objects can be created (called "instantiation").    The class (and consequently any object instantiated from it) are completely defined by the attributes that define its state and methods that define its behaviour.   For a discussion of OOP see section 4 of the Software Development learning module.   Smalltalk was the first purely object-oriented language, but object-oriented extensions have been added to many existing languages resulting in "hybrid" languages such as C++, Object Pascal, Ada 95, CLOS (object oriented Lisp), Object Logo, Prolog++, etc.  (Some of these are briefly described in the following section.)  Java, the fastest growing language in popularity (particularly for distributed systems like the Internet) is a purely object oriented programming language based on Smalltalk but with a syntax similar to C++.  (See below.)