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Java Programming
Introduction to
Java Programming
Cheng-Chia Chen
Feburary 2008
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Java Programming
Course web page
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Java Programming
Lecture 1. Introduction
Cheng-Chia Chen
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Java Programming
Contents
1.
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What is Java?
Features of Java
Evolution of Java
Develop first Java program
Deploy java programs through the internet
1. via Java applet
2. via Java Web Start
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Java Programming
What is Java?
Java is
 a programming language,
 defined in The Java language specification (v1,v2,v3)
 a virtual machine,
 Defined in The java virtual machine (v1, v2)
 a platform
 Standard edition (java se):
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Java platform standard edition 6.0
 Enterprise edition(j2ee): V5.0
 Micro edition (j2me): v1.0,CLDC1.1,MIDP2.0,…
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servers & enterprise computers
Java Programming
Desktop & personal computers
High-end consumer devices
Low-end devices
J2ME
smartcards
Java 2 Platform editions and their target markets
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 Java SE 6 Platform at a Glance
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What is J2EE ?
 source
 What is the Java 2 Platform, Enterprise Edition
(J2EE)?
 a platform that enables solutions for developing,
deploying and managing multi-tier server-centric
applications.
 Extend J2SE to a complete, stable, secure, fast Java
platform to the enterprise level.
 A platform which significantly reduces the cost and
complexity of developing multi-tier solutions, results in
services that can be rapidly deployed and easily
enhanced.
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Benefits of J2EE
1. Complete Web services support.
2. Faster solutions delivery time to market.
 Enterprise infrastructure and concerns provided and
solved by j2ee.
 Developers need only focus on writing business logic .
3. Freedom of choice.
 System assembled from standard components which can
be supplied by various vendors.
4. Simplified connectivity.
 Supply standard to connect legacy systems, enterprise
information system, and bring capability to web and
mobile devices.
5. Reduce TCO(total cost of ownership) and avoid
single-source for software needs of enterprises.
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Java Programming
Technologies included in J2EE
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Java API for XML-Based RPC (JAX-RPC),
JavaServer Pages, Java Servlets,
Enterprise JavaBeans components,
J2EE Connector Architecture,
J2EE Management Model,
J2EE Deployment API,
Java Management Extensions (JMX),
J2EE Authorization Contract for Containers,
Java API for XML Registries (JAXR),
Java Message Service (JMS),
Java Naming and Directory Interface (JNDI),
Java Transaction API (JTA),
CORBA, and
JDBC data access API.
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Java Programming
What is J2ME ?
 1.What is the Java 2 Platform, Micro Edition (J2ME)?
 The JavaTM 2 Platform, Micro Edition is the edition of the
Java 2 platform targeted at consumer
electronics and embedded devices.
 The J2ME technology consists of a virtual machine (KVM)
and a set of APIs suitable for providing tailored runtime
environments for consumer and embedded
electronics.
 Configurations v.s. profiles
 Device characteristics:
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memory size / processor
size and depth of display screen (UI)
power consumption (battery-based)
networking capability (limited, not TCP/IP based?)
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Java Programming
Features of the java language:
Java is
 simple
 object-oriented
 distributed
 interpreted
 robust
 secure
 architecture-neutral
 portable
 high performance
 multithreaded
 dynamic
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Java Programming
Java is Simple
 Intentionally created to be syntactically similar to C/C++
 Eliminates traditionally troublesome features of C/C++
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Pointer arithmetic
Multiple inheritance
Implicit type coercions
Explicit memory management
Preprocessor
 Eliminates features of C/C++
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struct
typedef
union
enum (recovered in jdk5.0)
(Programmer controlled) operator overloading
 Features included as part of base language:
 Threads
 Exception handling
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Java Programming
Java is Object-oriented
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Systems are built from sets of classes
Classes are instantiated at runtime to give objects
Objects communicate via messages passing
Everything is part of a class
supported OO Concepts:
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Data abstraction and Encapsulation
Inheritance
Polymorphism
Dynamic Binding
e.g. variable of Object type can hold everything
 Logical cluster of classes == package
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Java is a Distributed language
 Network programming support built into JDK class
library:
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TCP sockets
UDP packets
IP addresses
URLs
RMI (Remote Method Invocation)
Web Service
 Security features designed into language
 Network programming facilities are one of the
language's best features.
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Java is an Interpreted language
 Source code is initially compiled (javac) into
architecture-neutral byte-codes
 Byte-codes are interpreted by the java virtual
machine (JVM) (java or Netscape)
 Dynamic linking/loading (at run time)
 (Just In Time) JIT compilers lead to a large
performance increase in compilation and runtime
execution
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Java is Robust
 Strongly-typed language (cf Smalltalk and
VisualBasic)
 Compile-time and runtime checking
 No pointer arithmetic
 Exception handling
 Automatic memory management
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Java is secure
 Designed with security in mind.
 Allow users to download untrusted code over a
network and run it in a secure environment in which
it cannot do any harm.
 Configurable security levels and restrictions.
 subjected to intense scrutiny by security experts
with [potentially serious ] bugs found and fixed.
 become a big news if new bugs found!!
 One of the best mainstream platforms with the
strongest security guarantee.
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Java Programming
Java is Architecture-neutral
 Byte-codes are architecture neutral
 Performance suffers by using bytecodes
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Java is portable
 Primitive type sizes are explicit - not architecture
dependent
 Strings and characters are (16-bit) Unicode
compliant
 easier for internationalization.
 GUI libraries give a native graphic libraryindependent mechanism for creating quality
graphical interfaces (sort of)
 "They gave us a library that is good for writing programs
that look equally mediocre on the different systems."
(Core Java, page 9)
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Java Programming
High performance
 Interpreting leads to quicker development cycle
 Depends what you compare it to
 "Slightly faster than VB" - (Core Java, page 9)
 JITC(Just-In-Time Compiler) help greatly in this respect
 Sun’s Java HotSpot is Newest high performace JIT
compiler.
 Can use native code for mission-critical
performance sections of code
 JNI: Java Native Interface
 Sacrifice portability.
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Java Programming
Multithreaded
 Based on well-known 20 year old Hoare monitor
synchronization
 Thread support built into language
 Thread synchronization primitives supplied
 Garbage collector runs permanently as a low priority
background thread
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Dynamic
 Class linking, layout, name resolution and object
references not resolved until run-time
 Runtime Type Information (RTTI) available
 Can check the type of objects at run-time
 java.reflect.* package
 Class class for dynamic instantiation
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Can create objects of types unkown until runtime.
String sexClassName = getSex();
Object p = Class.forName(sexClassName).instance();
If(p instanceof Male) {…}
else if (p instanceof Female) { … }
else {… }
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Java Programming
An Example
/**
* The HelloJava class implements an application that
* simply displays "Hello Java!" to the standard output.
*/
class HelloJava {
public static void main(String[] args) {
// Display "Hello Java!"
System.out.println("Hello Java!");
}
}
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Prehistory of Java
 Green Project (1990)
 Consumer device operating software
 Requirements: small size, robust, portable, extremely reliable ,realtime performance
 Oak
 Originally used C++, then realized a new language was needed
 Original requirements same as for current language
 Java (1993)
 Intended market never eventuated
 WWW starting to takeoff
 Language design "based on" many current OO languages (e.g., C++,
Eiffel, Smalltalk, Cedar/Mesa, Objective C)
 1995/5/23 Sun launched Java
 JDK 1.0 released early 1996/1/23 ( 211 classes / 8 pkgs)
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Evolution of the Java Language
(8 packages)
(23 packages)
(59 packages)
(76 packages)
2001
(135 packages)
(166 packages)
(202 packages)
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Java Programming
Develop your first Java Program and applet
1. Required software
2. Creating Your First Application
a. Create a Java Source File
b. Compile the Source File
c. Run the Program
d. invoke the program remotely via Java Web Start.
3. Creating Your First Applet
a. Create a Java Source File
b. Create related HTML files
c. Compile and run the Source File
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Required Softwares
To write your first program, you will need:
1. The JavaTM 2 Platform, Standard Edition.
2. A text editor. Ex:
 NotePad,
 Ultraedit,
 EditPlus2
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2. Creating Your First Application
 The first program, HelloWorldApp, will simply
display : “Hello World!".
 Steps:
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a. Create a Java source file.
> Notepad HelloWorldApp.java
b. Compile the source file into a bytecode file.
> javac HelloWorldApp.java
c. Run the program contained in the bytecode file.
>java HelloWorldApp
d. invoke the program remotely via Java Web
Start.
d.1 :> jar cf HelloJWS.jar HelloWorlApp.class
d.2 : prepare HelloJWS.jnlp
d.3 : prepare web page to hyperlink
HelloJWS.jnlp
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HelloJava.java
/**
* The HelloWorldApp class implements an application that
* simply displays "Hello World!" to the standard output.
*/
class HelloWorldApp {
public static void main(String[] args) {
// Display "Hello World!"
System.out.println("Hello World!");
}
}
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JWS Architecture
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d. Invoke Java application remotely via JWS
<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0"
codebase="http://xml.cs.nccu.edu.tw/courses/java/jav
a2003fall/jws/"
href="helloJWS.jnlp">
<information>
<title>Hello Java Web Start</title>
<vendor>Cheng-Chia Chen</vendor>
<homepage href="index.html"/>
<description>A simpe Demo of Java Web
Start.</description>
<offline-allowed/>
</information>
<resources>
<j2se version="1.4+"/>
<jar href="helloJWS.jar"/>
</resources>
<application-desc main-class="HelloJWS"/>
</jnlp>
HelloJWS.jar
(web page)
…
<A href=“helloJWS.jnlp”>
Start HelloJWS
</A>
…
example
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Java 2 SDK Installation Instructions (for WIN32)
1. Download java SDK standard edition
2. Run the Java SDK executable (*.exe).
 determine where to install java se. (ex: c:\java\jdk6)
 > set JAVA_HOME= c:\java\jdk6
3. Update the PATH variable
 so that you can type ‘java’ instead of ‘c:\java\jdk6\bin\java’ to invoke java tools.
 > path=%JAVA_HOME%\bin;%PATH%
4. Check the CLASSPATH variable
 Used by java tools to determine where to find your personal (nonsystem) java class
files
 Types of java byte codes (class files):
 System : java tools know where to find them.
 Extensions: put in %JAVA_HOME%\jre\lib\ext
 Personal: via CLASSPATH or –cp/–classpath options
5. Start using the Java 2 SDK tools!
 java, javac, javadoc, jdb, javap,…
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3. Creating Your First Applet
a. Create a Java Source File: HelloJavaApplet.java
import java.applet.*;
import java.awt.*;
/**
* The HelloJavaApplet class implements an applet that
* simply displays "Hello World!".
*/
public class HelloJavaApplet extends Applet {
public void paint(Graphics g) {
// Display "Hello Java Applet!"
g.drawString("Hello world!", 50, 25);
}
}
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b. Create an HTML file to contain the applet.
<HTML>
<HEAD>
<TITLE>A Simple Program</TITLE>
</HEAD>
<BODY>
Here is the output of my program:
<APPLET CODE="HelloJavaApplet.class"
CODEBASE=“./applets/”
WIDTH=250 HEIGHT=25>
The applet does not work!</APPLET>
</BODY>
</HTML>
 Save this code to a file called HelloJavaApplet.html.
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c. Compile and run the program
 Compile the Source File.
 Javac HelloJavaApplet.java
 Run the program:
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With Appletviewer:
appleviewer HelloWorld
With IE explorer, Netscape:
double click HelloJavaApplet.html
 demo
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How java code are structured ?
 A java application consists of
 = many packages [from JRE + from 3rd party + your own ]
 A package consists of
 many classes
 many subpackages
 Note: importing a package does not mean importing
its subpackages.
 A java source file xxx.java is called a compilation
unit, which may
 contain multiple java class definitions and
 may be compiled into multiple java byte code (***.class ).
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 A class has two names:
 simple name
 fully qualified name = package name. SimpleName
 Ex:
 java.lang.String
 javax.swing.JButton
 The package/subpackage/class structure is not only
logically analogous to directory/subdirectory/file in
OS file system but in fact they are stored physically
in file system in this way.
 Namely, if package p corresponds to a directory d then
subpackage p.q of p would be stored in subdirecty q of d,
and class p.A of p would be stored in file named A.class or
A.java.
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 How does java machine find a class or src x.y.z.A in
the package x.y.z ?
 Notes:
Ex
 package x.y.z is a subpackage of x.y, which is a
subpackage of x.
 we called package x, java, javax etc, top-level packages.
 java find the location of top-level packages from a list of
directory given by a system variable called CLASSPATH.
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Ex: If CLASSPATH = .;d:\my\root Then
package x is the dir d:\my\root\x or ./x
package x.y is the dir d:\my\root\x\y or ./x/y
package x.y.z is the dir d:\my\root\x\y\z or ./x/y/z
class or src .y.z.A is the file d:\my\root\x\y\z\A.class
or d:\my\root\x\y\z\A.java or …
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