Introduction to Java Programming

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Introduction to Java Programming

• Cheng-Chia Chen
• Feburary 2008

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Course web page
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Lecture 1. Introduction

• Cheng-Chia Chen

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Contents

• What is Java?
• Features of Java
• Evolution of Java
• Develop first Java program
• Deploy java programs through the internet
• via Java applet
• via Java Web Start

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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)
• 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
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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Technologies included in J2EE

• 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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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
• 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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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 is Simple

• Intentionally created to be syntactically similar
  to C/C
• Eliminates traditionally troublesome features of
  C/C
• Pointer arithmetic
• Multiple inheritance
• Implicit type coercions
• Explicit memory management
• Preprocessor
• Eliminates features of C/C
• 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 is Object-oriented

• 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
• 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
• 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 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
  library-independent 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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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
• Suns 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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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
• 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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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 ,real-time 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
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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
• a. Create a Java source file.
• gt Notepad HelloWorldApp.java
• b. Compile the source file into a bytecode file.
• gt javac HelloWorldApp.java
• c. Run the program contained in the bytecode
  file.
• gtjava HelloWorldApp
• d. invoke the program remotely via Java Web
  Start.
• d.1 gt 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
(web page)
lt?xml version"1.0" encoding"utf-8"?gt ltjnlp
spec"1.0" codebase"http//xml.cs.nccu.edu.
tw/courses/java/java2003fall/jws/"
href"helloJWS.jnlp"gt ltinformationgt
lttitlegtHello Java Web Startlt/titlegt
ltvendorgtCheng-Chia Chenlt/vendorgt lthomepage
href"index.html"/gt ltdescriptiongtA simpe
Demo of Java Web Start.lt/descriptiongt
ltoffline-allowed/gt lt/informationgt
ltresourcesgt ltj2se version"1.4"/gt
ltjar href"helloJWS.jar"/gt lt/resourcesgt
ltapplication-desc main-class"HelloJWS"/gt
lt/jnlpgt
ltA hrefhelloJWS.jnlpgt Start HelloJWS lt/Agt
example
HelloJWS.jar
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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)
• gt 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.
• gt pathJAVA_HOME\binPATH
• 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.

• ltHTMLgt
• ltHEADgt
• ltTITLEgtA Simple Programlt/TITLEgt
• lt/HEADgt
• ltBODYgt
• Here is the output of my program
• ltAPPLET CODE"HelloJavaApplet.class"
• CODEBASE./applets/
• WIDTH250 HEIGHT25gt
• The applet does not work!lt/APPLETgt
• lt/BODYgt
• lt/HTMLgt
• 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
• 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/subdirector
  y/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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Ex

• How does java machine find a class or src x.y.z.A
  in the package x.y.z ?
• Notes
• 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.
• 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