Lecture 2 - History of OOP and Java

1

A BRIEF HISTORY OF OOP

AND

JAVA PROGRAMMING
LANGUAGE


Ziya Karakaya






Atılım University

Tel: (312) 4602020 / 5345 Faks: (312) 460 20 37

E
-
posta: ziya
@atilim.edu.tr



2

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

3

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.

4

Why Java ?


We w
ill 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


5

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.

6

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.

7


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!

8

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
.


9

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.


10

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.

11

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.

12

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.

13

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.


14

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.

15

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.

16


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
.

17

18

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”

19

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.

20


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.

21

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)

22

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.


23

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.

24

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.

25

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.

26

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.

27

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.


28

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.

29

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.

30

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.