Download Introduction to Java and Applet

Introduction to
Java and Applet
Lecture 3 from Chapters 1
and 2 of the complete
reference
1
Java’s Lineage
• Java is related to C+.
• Java is a direct descendent of C.
• Java’s object-oriented features were
influenced by C++
• Java was developed by James
Gosling etc. at Sun Mircosystems in
1991.
• It was called “oak” and was renamed
as Java.
2
Java and the Internet
• Java is a portable, platformindependent language that could be
used to produce code that would run
on different platform.
• Java expands the universe of objects
that can move freely in Cyberspace.
• It is ideal for client [windows]-server
[linux] platform.
3
Java Applets
• Java supports two types of programs:
applications and applets
• An application: It is a program that
runs on our PC under windows XP.
• An applet: It is a tiny Java program,
dynamically downloaded across the
network, like music, video clip.
4
Security
• Without Java, Once you are downloading
an executable program, there is a risk of
viral infection.
• If it is written in Java using Javacompatible browser, it is pretty safe.
• Java also provides a “firewall” between a
networked application and our PC to safeguard information such as credit card
number, bank account balance.
5
Java’s Merit-
Interpreter and Bytecode
• Java that resolves security and portability
problems is because the output of a Java
Compiler is not executable code (not .exe
or .com).
• It is bytecode.
• Bytecode is an optimised codes to be
executed by the Java Run Time system.
• Java run-time system is an interpreter.
6
Java Overview –
some key elements
• Simple: simple and easy to learn
• Object-oriented: Clean, usable approach
to objects
• Robust: reliable under different operating
environments across the networks (The
Internet)
• Mutlithreaded: supports a few light weight
processes
• Interpreted: Although it is an interpreted
language, the performance is good.
7
Download Java Compiler (1)
8
Download Java Compiler (2)
9
Download Java SDK (3)
10
Installing StandardSDK
Java 2
11
Installation -
check whether you
have installed java and javac
12
Set the path to include the directory
Test it by typing javac in other directory
13
JDK components
• appletviewer.exe
• java.exe
• javac.exe
• javadoc.exe
• javap.exe
• jdb.exe
applet viewer
intepreter
compiler
document generator
decompiler
debugger
14
A simple Program – javac & java
15
Explanation to the first program
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Explanation to the first program
• Class: First is the name of class. It will
generate a First.class after compilation
(javac)
• Public: is an access specifier that allows
the programmer to control
• Main(): must be declared as public so that
it can be accessed.
• String args[]: argv[0] is the first
argument
• System.out.println: Display the contents
followed by a line feed
17
Second Program
18
Second Program Explanation
• int num; declares an integer valuable
called num
• Num = 10; assign a value of 10
• System.out.println("The value of
num is " + num); The “+” causes
the value of num to be displayed
• .println() ; displays the string passed
• .print(); display the string without
line feed
19
Applet (1)
20
Applet (2) – the result
21
Explanation to Applet
• Prepare a java
program called third
• In the HTML, specify
the class of the
program (third)
• Use appletviewer or IE
explorer to see the
result
22
Javadoc - Document Generator
23
Javadoc – some example
24
Javadoc.exe
• Javadoc is a tool shipped with JDK
that generates HTML documentation
from the comments in the class
source files.
• With the aid of Javadoc we can
simplify documentation of our code
and make it a regular habit.
25
Javap – decompiler
26
Javap - explanation
• The javap
command
disassembles a
class file.
• Its output depends
on the options
used. If no options
are used, javap
prints out the
package.
27
Jdb – Debugger
28
Jdb - explanation
• The Java Debugger, jdb, is a simple
command-line debugger for Java
classes.
• It provides inspection and debugging
of a local or remote Java Virtual
Machine.
• Jdb class  format
29
Jdb – help
30
Summary
• Java is related to C+.
• Java is a direct descendent of C.
• Java’s object-oriented features were
influenced by C++
• It is ideal for client [windows]-server
[Linux] platform.
31