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Java History

VIEWS: 296 PAGES: 31

									    A BRIEF HISTORY OF OOP
              AND
JAVA PROGRAMMING LANGUAGE


       -Akash Padhiyar

                             1
History of Object-Oriented
Programming Languages
   Almost all major concepts of OOP, such
    as objects, classes, and inheritance
    hierarchies, were developed in the 1960s
    ◦ Simula language, by Norwegian Computing
      Center
   In the 1970s, Alan Kay developed Smalltalk
    language at Xerox PARC (the Palo Alto
    Research Center)
    ◦ targeted to be understandable to people with
      no prior training in computer use
    ◦ demonstrated by experiments conducted
      using children as programmers
                                                     2
History (cont’d)
   Bjarne Stroustrup at Bell Labs who had
    learned Simula during his Ph.D. studies
    developed C++ as an extension of C

   Later many other OOP languages were
    developed: Eiffel, Objective-C, Actor, Object
    Pascal, etc.

   Since 1986 (first OOPSLA conference) OOP
    is a mainstream player in the PL domain the
    rather than a revolutionary one.

                                                    3
Why Java ?
   We will explore the OOP in the context
    of Java programming language.
    ◦ OOP has been a hot topic for over a decade
    ◦ Java has recently become the commonly
      perceived embodiment of object-oriented
      ideas




                                                   4
Java Programming Language
   Java is a general purpose programming
    language that can be used to create
    almost any type of computer program.

    ◦ Especially, it can be used to create programs
      intended for execution across the Internet.




                                                      5
       The History of Java
 It was named Oak in 1991 at Sun Microsystems.
 A computer scientist, James Gosling, developed
  Oak for use in embedded consumer electronic
  applications, such as VCRs.
    ◦ This development purpose has determined many of
      the characteristics of the language.
    ◦ Size and reliability are key features.
      The processors that run in embedded systems are very
       small and has very little memory. A program must be able to
       be translated into a very concise encoding.
      Embedded systems should almost never fail.


                                                                 6
   Java has these features.
    ◦ Pointers and goto statement were eliminated.
    ◦ Exception-handling is enforced to handle the
      unexpected in a graceful fashion


   Unfortunately, Java (or Oak) as a language
    for embedded consumer electronics did
    not materialize at that time!


                                                     7
Evolution of World Wide Web
   World Wide Web was developed in the early
    1990s by a small group of scientists at a
    research lab in Switzerland.
    ◦ As a mean of quickly communicating research
      results to a physically far-flung set of colleagues.
   To understand how Java fits into the WWW,
    one must understand about the concepts of
    clients and servers and the difference
    between server-side computing and client-side
    computing.
                                                             8
Client-Side Computing
 The Internet is a classic example of a client/server
  system.
 A person using the Internet works at his or her own
  computer, which runs an Internet-aware application,
  such as a Web browser. This is called the client system.
 The client application communicates over the Internet
  with another computer. For example, a Web browser
  might request the information on a Web page stored on
  a distant computer.
    ◦ This computer is the server computer.
   The client computer then determines how to display
    this information to the user.


                                                             9
Client-Side Computing
   In the past these programs are executed on the server
    computer. The client transmitted a request, and the
    server responded by executing a program and
    transmitting the result.

   Several performance problems occur
    ◦ There exists a delay between the moment when the client
      asks that a program be executed and the time the results
      are returned.
    ◦ Server programs often deal with many clients at once,
      reducing performance.


                                                                 10
Client-Side Computing
 In client-side computing, rather than
  executing the program on the server side
  and transmitting the result, the server will
  transmit the program to the client.
 The client will execute the program
  locally.
 Advantages:
    ◦ Program run on a less heavily loaded system
    ◦ Only delay is the time to transmit the
      program – user interactions take place locally.

                                                        11
Bytecode Interpreter and Just In Time
Compilers
   Client many not know what type of machine the server
    is using.
    ◦ The traditional concept of computer programs being
      translated into machine code for a specific machine will
      not work.
   Java is translated into a device-independent bytecode.
    ◦ This Bytecode is like a machine language for an imaginary
      machine, a Java-specific machine, or Java Virtual Machine
      (JVM)
   Each computer that runs Java programs then processes
    these bytecodes into a form that works correctly on
    the current system.

                                                                  12
Interpreters vs. JIT Compilers
   The easiest scheme is to have an interpreter
    that reads and executes bytecodes one by
    one.
   A better performance can be obtained by
    using a just-in-time (JIT) compiler.
    ◦ This system takes the Java bytecodes and
      translates them into the machine code native to
      the client system.
    ◦ These programs then run as fast as any compiled
      program created specifically for the client
      computer.

                                                        13
       Security Issues
   A program running on the client side could
    have full access to the client computer
    resources.
    ◦ There is potential for such a program to do
      significant damage, such as erasing files from a
      hard drive.
   Java programs use a security manager provided
    by the client.
    ◦ It limits the actions that can be performed by the Java program
      provided by the server.
    ◦ For example, no access to the file system or access to other
      machines across the Internet.

                                                                        14
Specialization of Interfaces
 The sequences of commands needed to
  perform graphical operations varies
  greatly from one machine to another.
 The solution to this problem requires a
  careful coordination between the client
  and server computers.
    ◦ Portions of a Java program originating on one
      machine, and other parts coming from the
      second.
    ◦ The server program is structured in terms of
      generic classes, such as Window and Button.

                                                      15
 Generic classes are the same regardless
  of the type of system on which the Java
  program is run.
 When executed, these components
  create a peer component.
    ◦ The peer component originates on the client
      system and is not part of the server program.
    ◦ Thus, a button running on a PC will create a
      PC-Button peer, while the same program
      running on a Macintoch will create a Mac-
      Button peer.

                                                      16
17
The White Paper Description
   Java is a simple, object-oriented, network-
    savvy, interpreted, robust, secure,
    architecture neutral, portable, high-
    performance, multithreaded, dynamic
    language.

       “A buzzyword heavy description”




                                                  18
      Java is Simple
   Simpler than C++:
    ◦ No preprocessor.
    ◦ Far fewer special cases.
    ◦ No confusing features such as overloaded
      operators, independent functions, global variables,
      goto statement, structures, or pointers.
   Augmented with a larger library of high-level
    development tools.



                                                            19
A Remark on Pointers
   In many languages, there is a distinction
    between a value vs. a pointer to a value:
    ◦ Values are static, fixed-size entities
    ◦ Pointers are dynamic quantities filled at run-time.
   There are important reasons why object-oriented
    language should make heavy use of pointers.
    ◦ Java does so, but implicitly. Everything is internally a
      pointer.
    ◦ Elimination of this construct removes common errors,
      making it easier to construct reliable and correct
      programs.


                                                                 20
Java is Object-Oriented
   Java has no functions and no variables that
    can exist outside of class boundaries.
    ◦ Thus, all Java programs must be built out of
      objects.
   C++ and Object Pascal (Delphi) combine
    OO features on top of an existing, non-
    object-oriented language.
    ◦ Programmers can continue working in old, non-
      object-oriented fashion.
   By forcing all programs into an object-
    oriented structure, benefits of OO are
    realized. (encapsulation, reusability)

                                                      21
Java is Network Savvy
 The language provides a rich set of tools
  for programming across a network.
 The Java standard library provides classes
  for describing universal resource locators
  (URLs) and for execution in controlled
  environments such as a World Wide Web
  browser.



                                               22
Java is Interpreted
 Java was designed for a multicomputer execution
  environment.
 Any type of computer could be used as a Java virtual
  machine.
 Java programs were compiled into bytecodes , could be
  stored on any type of machine. An interpreter would
  read the bytecodes and execute them.
    ◦ Interpreters are much slower in execution.
   A just-in-time (JIT) compiler is a system that read
    machine-independent bytecode and translates them into
    actual machine instructions.


                                                          23
Java is Robust
   The Java language and associated libraries
    are designed to be graceful in the presence
    of hardware and software errors.
    ◦ The use of exception handling.
    ◦ Programmers are forced into thinking about
      potential source of errors.
   Java has an automatic memory management,
    garbage collection.
    ◦ It detects and recovers memory that is no longer
      being used by the current running program.

                                                         24
      Java is Secure
   Multi-level Security System
   First Level:
    ◦ Eliminating pointers remove the most common errors.
    ◦ The Java language insists that array index values are cheked
      before the are referenced.
    ◦ All variables must be assigned values before being used.
   Second Level:
    ◦ Bytecodes are checked for common errors.
       Such as they do not access classes incorrectly, overflow or
        underflow the operand stack, or use illegal data conversions
    ◦ Java programs are restricted in the type of operations they can
      perform.
       When they execute a program brought over the network, their
        local computers are safe from tampering.
                                                                        25
Java is Architecture Neutral
   Java bytecodes work with all machines.
    ◦ A Java program is the same whether it runs
      on a PC. a Macintosh, or a Unix system.
   C++ libraries differ from one platform to
    another.
    ◦ Thus, it is difficult to move programs designed
      for the PC onto a Macintosh.
   Java hides these application-specific details
    under a layer of abstraction in the
    standard Java library.

                                                    26
Java is Portable
 Java programs are portable because the
  Java library hides architecture-specific
  concepts and bytecodes are the same for
  all machines.
 The exact same program can be compiled
  on one system, then executed on many
  different types of systems.



                                         27
Java is High-performance
   Just-in-time compilers allow platform-
    dependent Java programs to be executed
    with nearly the same run-time
    performance as conventional compiled
    languages.




                                             28
Java is Multithreaded
   Java is one of the first languages to be
    designed for multiple threads of execution
    running in one program.
    ◦ It is easy to set up multitasking.
    ◦ The coordination of these parallel processes
      is also relatively simple.




                                                     29
Java is Dynamic
   Because Java programs move across the
    Internet and execute on the user’s local
    computer, they permit a degree of
    dynamic behaviors impossible in older
    style systems.




                                               30
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