Java – in context - ITS: Publishing Academic Web Pages

Java
–

in context

Main Features

From Sun Microsystems ‘White
Paper’

Features:

•
simple

•
object oriented

•
network
-
savvy

•
interpreted

•
robust

•
secure

•
architecture neutral

•
portable

•
high
-
performance

•
multithreaded

•
dynamic

The language itself

•
Java does not allow pointers

•
Java is strongly typed

•
Java completely object
-
oriented

•
Java prevents programmer from accessing a
non
-
initialized variable

The Verifier

•
When Java byte code arrives for execution
the Verifier checks it to ensure that it is safe

•
No dangerous pointers

•
Access to private variables and methods
valid

•
Methods invoked with correct type
parameters

•
No illegal data conversions are done

The class loader

•
The class loader carefully distinguishes
between different packages and particularly
between local built and classes and any
others (it’s not nice to try to fool Java)

The Java Virtual Machine (JVM)

•
Once code is checked, byte code is not
directly executed on the machine but is
interpreted

Arrays

•
Subscripts must be within bounds

Garbage Collection

•
When an object in a Java program is no
longer needed, the system automatically
releases the memory that was allocated to it.

•
That memory can then be reused if needed

The filing system

•
Java applet can control that applet’s access
to files by specifying an option to the
browser.

•
The user can decide (for example) to read
but not write to a local file (default applets
can not read/write to users files unless given
permission)

Summary

•
Java provides several mechanisms for
protection

•
The language and the compiler
–

e.g.
absence of pointers

•
Verification of byte code

•
The class loader

•
The filing system and network access

Thin clients

•
PCs connected to others rather than all stand alone

•
PC does not need its own hard disk and filing
system software.

•
Organizations have hundreds of PCs (cost a
factor) to upgrade hardware and software. Time
spent to install software, file back ups etc.

•
Thin client eliminates all these costs.

•
Java strongly supports networking
–

and Java
compilers can be downloaded

Microsoft vs. the world

•
Text gives a very concise history of
Windows O.S. and the Intel Corp.

•
The U.S. government lawsuit now seems to
have been settled. (individual states have
not yet signed off)

•
C# Microsoft OO language based on C++

Versions of Java

•
1. Standard

•
2. Enterprise

•
3. Micro

•
(Personal Java for PDAs etc.)

Java capabilities

•
Enhancements to Java through the addition
of new libraries

•
Java Libraries: (small language powered by)

•
Java Language and Utilities

•
Java Electronic Commerce Framework

•
Java Security

•
Java Media Framework

•
Java Collections Framework

•
Java 3D

Internationalization

•
Different languages have different character sets

•
Dates and times (UK day/month/yr
–

US
month/day/yr)

•
Currency Different currency symbols

•
Java classes which help
–

Unicode character
standard

•
1. Classes ‘locale’ an area with its own language
classes do the appropriate formatting of currency,
date and time

•
2. Unicode 16
-
bit (used for file I/O)

Databases
–

JDBC


•
Databases are big business

•
Aside from word processing, spreadsheets
and email the database can be regarded as
the most vital software component of a
business

•
Java Database Connectivity (JDBC)

•
JDBC allows access to SQL
-
compatible
databases

RMI
–

Remote Method
Invocation

•
With the tremendous increase in Internet use. The
idea of interacting with programs on other
machines is mainstream. In the corporate
computing area as well, networks are the norm.

•
A possible arrangement for the drawing example
in the text each PC (or server) would have a local
program to handle drawings and one on the server
to broadcast new input. (known as RMI user
invokes methods on the server)

Java Beans

•
‘a reusable software component that can be
manipulated visually in a builder tool’

•
The software into which a bean is to be
placed is written in such a way as to allow
the bean to be incorporated.

•
To incorporate the bean into an application,
a special bean development environment

•
(BDK Beans Development Kit) from Sun

Java servlets


•
Web interaction is enabled by programs on a
server computer interacting with software
(browser typical) on a client computer.

•
Benefits:

•
Each use of the Web page results in data being
sent to server, the servlet produces a thread

•
Servlet run in sandbox (safe and secure)

•
Platform independent (if allowed)

Javascript

•
Scripting language

•
No language features common with Java

•
Concepts similar to Java

Conclusion
–

trends in computer
industry

•
Tremendous growth of Internet

•
Importance of Web interaction

•
Use of intranets (within a corporation
–

example)

•
Reduction in cost of networking

•
Fusion of computer and telecommunications

•
Incorporation (embedding) of computers within
consumer products

•
Multimedia

Conclusions
-

continued

•
Vital need for secure computing across the
networks

•
Fight against Microsoft dominance
(Windows O.S.) and Intel (PCs).