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School of Computer Science &
Information Technology
G6DICP - Lecture 2
The Java Programming Language
Programming Languages
2
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Formal languages in which computer programs
are written
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All languages consist of syntax and semantics
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Low level languages - close to machine code
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High level languages - further removed from
machine code
Language Generations
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3
First: Raw machine code
Second: Assembly language (NB processor
dependent)
Third: High level languages (eg Java, C, Fortran,
Cobol etc)
Fourth: Application languages (eg SQL, Postcript
Fifth: AI languages (expert systems, fuzzy logic,
neural networks etc)
Computer Programs
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4
Computers are "stupid"
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Mathematical and logical instructions are executed very
quickly and accurately.
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They obediently but stupidly do what you tell them to - not
necessarily what you want them to!
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Tiny errors in a program can cause major problems when it is
executed.
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Always remember syntax as well as semantics!
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Careful planning is essential
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Flow charts are a useful tool to represent program flow visually.
Kettle-Boiling Program
Is Kettle full?
Yes
Boil Kettle
Make Tea
5
No
Fill Kettle
Components of
Tea Making Program
Fill Kettle
Boil Kettle
Place kettle
under tap
Place Kettle
on hob
Open tap
Turn on heat
Wait
Wait
No
Is kettle full?
Yes
Close tap
6
Is kettle boiling?
Yes
Turn off heat
Kettle-Boiling Program
Fill Kettle
Place kettle
under tap
Is Kettle full?
No
Open tap
Wait
No
Is kettle full?
Yes
Yes
Boil Kettle
Place Kettle
on hob
Turn on heat
Wait
Is kettle
boiling?
Yes
Turn off heat
Make Tea
7
Close tap
What is Java?
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Java is a programming language
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Java is not only for web programming
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Created by Sun Microsystems
Often used for web programming
Initially marketed as a web development system
General purpose programming language
Very similar to C++ - simplified!
Features of Java
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Originally developed for hardware devices.
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Platform Independent Binaries
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Most operating systems
Also hardware devices
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Robust and easy to use
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Object Oriented and highly modular
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Internationalisation
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Networking and Security features
Java Model
Byte Code
Virtual Machine
Operating System
Hardware
10
Java VM Platforms
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Sun supported platforms
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Third party platforms (freely licensed)
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Solaris
Win32 (Windows 95/98 & NT)
Linux
“Hardware”
Other Unix
Mac OS
Palm OS
Symbian
and many others
Types of Java Programs
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Applications
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Applets
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Delivered over the Internet
Require a Java capable WWW browser
Servlets
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12
Standalone programs
Require a VM
Require a Java capable WWW server
Java Application
Storage
Source Code
Byte Code
CPU/memory
Compiler
Interpreter (VM)
Program
Execution
13
Java Applet
Web Server
14
HTML
Byte Code
Web Browser
Web Browser
Program Execution
(embedded in web page)
Program Execution
Development Software
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Java Developers Kit (JDK)
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Freely available from Sun for most platforms
“no frills” development
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Compiler - javac
Interpreter - java
Applet viewer - appletviewer
Utilities (auto-documentation, debugging, optimisation etc)
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Java Runtime Environment (JRE)
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Integrated Development Environments / RAD Systems
Flavours of Java
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JavaScript
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This is not Java!
Java Versions
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Very obsolete
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Obsolete
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JDK 1.1
Java 2
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JDK 1.0
JDK 1.2, 1.3 & 1.4
Third party VM’s