Download Java History:

JavaIntro 1/2
Java History:
Java was designed for writing programs for small computers embedded in
consumer electronics appliances. The design choices reflect the
expectation that the language would be used to implement small,
distributed, and robust programs.
Certain features happen to make Java the ideal language for building
programs for use on the Internet:
-- run on wide variety of hardware platforms
-- can be loaded dynamically via a network
-- provides features that facilitate robust behavior
Additional nice features include:
-- pure object-oriented language (everything is an object)
-- can work on multiple tasks simultaneously
-- automatically recycle memory (called garbage collection)
To make Java programs portable, they are translated into byte code by a
Java compiler. (Byte code is an intermediate language in the compiler
phases.) Programs translated into byte code are machine independent
(front-end). The byte code is executed by a byte code interpreter,
called Java Virtual Machine (JVM) (back-end). So, any Java application
will run on every machine for which a Java virtual machine has been
implemented (called a hybrid compiler/interpreter).
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source ---> | front end |---> intermediate --> | back end |---> machine
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language
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code
machine
machine
independent
dependent
When you run a java program, each class definition is fetched by your
program only when it is needed. So, Java loads classes dynamically.
Can be used with a network browser containing a JVM capable of loading
classes dynamically via a LAN or the Internet.
Java application loaded by the web browser are called applets, a little
application. (Easy and cheap to distribute software -- no CDs, disks,
no updates.)
JavaIntro 2/2
Java is comprised of these parts:
* Java programming language -- with which Java applications are written.
* Java Virtual Machine (JVM) -- an interpreter that runs compiled Java
code.
* Java runtime environment -- a predefined set of classes present in
every Java installation, called packages, with each package
oriented about some functionality (such as graphics,
input/output, networking).
Characteristics of Java:
* Portable: An application written in Java will run on any operating
system that supports the JVM. "Write once, run anywhere" is the
motto.
* Versions: Java
Java 1.1 had
Java 1.2 has
Java 1.3 has
1.0 had 212 classes in 8 packages.
504 classes in 23 packages.
1520 classes in 59 packages.
updates and corrections.
* Free for Windows, Linux, and Solaris operating systems. Downloadable
Software Development Kit (SDK), also known as the Java Development
Kit (JDK), from http://java.sun.com .
* Security: the language and the runtime environment were designed with
security in mind. One can download software over the network,
run it, and be assured that the program will not transmit a virus,
read or write files on the hard drive, or crash the system.
Has extensive, configurable permissions for restricting or
enabling applications.
* Networking: Very easy to write network applications using Java
(compared with C/C++).
* Internationalized: Designed to be used by all languages.
The character type is 16 bit unicode, which supports all human
languages. Has extensive international formatting capabilities
for time, dates, currency, numbers, etc.
* Performance: Java is an interpreted language, so it will generally be
slower than languages compiled directly into machine language (as
with C/C++). But the speed of execution within the JVM often is
nearly as good as compiled C.