Introduction to Java
Introduction to Java
- Java was originally developed at Sun Microsystems
in 1991 to provide a platform-independent
programming language and operating system for consumer
electronics (TV sets, toasters and VCRs).
- In syntax and execution, Java is a
lot like a simplified version of C++. ("simplified" should be
read in the previous sentence as "an improved"). It is a
highly robust, distributed, high performance, object-oriented,
multi-threaded language with all of the usual features.
As such, it builds upon years of C++ development, taking the
good and dispensing with the bad.
- As it so happened however, Java did
not make it into the consumer electronics market. Instead it
wound up in our web browsers.
- Java seemed to be a perfect fit for
the web. The language itself was extremely small (as it was
built to go inside toasters and alarm clocks with tiny
amounts of memory). Thus it could quickly be transferred over
the web.
- Further, Java was platform
independent. That is, any computer with a Java virtual
machine can run a Java program. Programs can be written
anywhere and be run anywhere. This is crucial because if a
language can not run on any machine, it cannot be used on the
web that must service every machine, language, and environment
imaginable.
- Platform independence works because
Java is an interpreted rather than a compiled language.
Unlike C or C++ code, when Java is compiled, it is not compiled
into platform specific machine code, but into platform
independent byte code. This byte code is distributed over the
web and interpreted by a virtual machine (typically built
right into a web browser these days) on whichever platform it
is being run. Perhaps a
picture would be useful...
- Thus, as a programmer, you need only
concern yourself with the generic Java programming language
and compile your applications into bytecode on whatever system
you are using. You can then be assured that your bytecode will
be executed correctly whether your clients are using Macs,
Pcs, Unix boxes or anything else.
- Perhaps the best summary of the
design goals and accomplishments of Java comes from Gary
Cornell in the introduction to Core Java. In this
introduction, Cornell outlines 12 design principles used in
the development of the Java language. To do so, he quotes
from the Java White Paper from Javasoft. I will duplicate the
quotes here, but you should not consider your Java Library
complete without a copy of Core Java.
Java is Simple
"We wanted to build a system that
could be programmed easily without a lot of esoteric training
and which leveraged today's standard practices...So even
though we found that C++ was unsuitable, we designed Java as
closely to C++ as possible in order to make the system more
comprehensible. Java omits many rarely used, poorly
understood, confusing features of C++ that, in our
experience, bring more grief than benefit."
Java is Small
"Another aspect of being simple is
being small. One of the goals of Java is to enable the
construction of software that can run stand-alone in small
machines."
Java is Object Oriented
"Simply stated, object-oriented
design is a technique that focuses design on the data
(= objects) and on the interfaces to it...The object-oriented
facilities of Java are essentially those of C++."
Java is Distributed
"Java has an extensive library of
routines for coping with TCP/IP protocols like HTTP and FTP.
Java applications can open and access objects across the net
via URLs with the same ease as when accessing a local file
system."
Java is Robust
"Java is intended for writing
programs that must be reliable in a variety of ways. Java
puts a lot of emphasis on early checking for possible
problems, later dynamic (run time) checking, and eliminating
situations that are error prone."
Java is Secure
"Java is intended to be used in
networked/distributed environments. Towards that end, a lot
of emphasis has been placed on security. Java enables the
construction of virus-free, tamper-free systems."
Java is Architecture Neutral
"The Java compiler [generates]
bytecode instructions which have nothing to do with a
particular computer architecture. Rather, they are designed
to be both easy to interpret on any machine and easily
translated into native machine code on the fly."
Java is Portable
"Unlike C and C++, there are no
'implementation-dependent' aspects of the specification.
[For example,] the sizes of primitive data types are
specified, as is the behavior of arithmetic on them"
Java is Interpreted
"The Java interpreter can execute
Java bytecode directly on any machine to which the
interpreter has been ported. [Thus] the development process
can be much more rapid and exploratory."
Java is High Performance
"While the performance of interpreted
bytecode is usually more than adequate, there are situations
where higher performance is required. The bytecode can be
translated on the fly into machine code for the particular
CPU the application is running on."
Java is Multithreaded
"The benefits of multithreading are
better interactive responsiveness and real-time behavior.
[This is because a program can do more than one thing at a
time]"
Java is Dynamic
"In a number of ways, Java is a more
dynamic language than C or C++. It was designed to adapt to
an evolving environment...Libraries can freely add new
methods and instance variables without any effect on their
clients."
Introduction to Java Resources
Reading and Parsing Form Data with cgi-lib.pl
Table of Contents
Introduction to Object Oriented Design
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