What is Java?

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What is Java?

• Object Oriented Programming Language
• Sun Microsystems
• Write Once, Run Everywhere
• Bytecode and Virtual Machine
• Java Platform (Java VM and Java API)

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Java History

• Started 1991 by Gosling, Sheridan, Naughton (The
  Green Team)
• Oak for Consumer Electronics
• Mosaic 1993
• March 1995 v1.0a2
• Netscape and Java, May 23, 1995

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Java As Programming Language

• Simple
• Object-Oriented
• Distributed
• Interpreted
• Robust
• Secure

• Architecture Neutral
• Portable
• High-Performance
• Multithreaded
• Dynamic

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What you get with Java

• The essentials Objects, strings, threads,
  numbers, input and output, data structures,
  system properties, date and time, and so on.
• Applets The set of conventions used by applets.
• Networking URLs, TCP (Transmission Control
  Protocol), UDP (User Datagram Protocol) sockets,
  and IP (Internet Protocol) addresses.

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• Internationalization Help for writing programs
  that can be localized for users worldwide.
  Programs can automatically adapt to specific
  locales and be displayed in the appropriate
  language.
• Security Both low level and high level,
  including electronic signatures, public and
  private key management, access control, and
  certificates.
• Software components Known as JavaBeans, can plug
  into existing component architectures.

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• Object serialization Allows lightweight
  persistence and communication via Remote Method
  Invocation (RMI).
• Java Database Connectivity (JDBC) Provides
  uniform access to a wide range of relational
  databases.

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Object Oriented

• Data Structure and behavior are incorprated in
  discrete objects
• identity, classification, polymorphism,
  inheritance
• Identity Data is quantized into discrete,
  distinguishable entities called objects.
• Classification Objects with same attributes and
  behavior are grouped in classes

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• Class An abstraction that describes properties
  important to an application and ignores the rest
• Instance Each object is an instance of a class.
• Polymorphism Same operation may behave
  differently on different classes. Specific
  implementation of an operation is a method.
• Inheritance Sharing of attributes and operations
  among classes based on a hierarchical
  relationship

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OO Development

• Model Concepts Not Implementation
• Analysis
• System Design
• Object Design
• Implementation

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Key Themes

• Abstraction Focus on the essential, inherent
  aspects of an entity and ignoring the accidental
  properties
• Encapsulation or Information Hiding Separate the
  external aspects of an object from the internal
  implementation details
• Combine Data and Behavior

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• Sharing
• Emphasize object structure not procedural
  structure
• Synergy

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Hello World
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Comments
The Java language supports three kinds of
comments / text / The
compiler ignores everything from / to /.
/ documentation / This indicates a
documentation comment (doc comment, for short).
The compiler ignores this kind of comment, just
like it ignores comments that use / and /.
The JDK javadoc tool uses doc comments
when preparing automatically generated
documentation. For more information on javadoc,
see the Java tool documentation. // text
The compiler ignores everything from
// to the end of the line.
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Applet
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HTML
ltHTMLgt ltHEADgt ltTITLEgt A Simple Program
lt/TITLEgt lt/HEADgt ltBODYgt Here is the output of my
program ltAPPLET CODE"HelloWorld.class"
WIDTH150 HEIGHT25gt lt/APPLETgt lt/BODYgt lt/HTMLgt