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CS2200 Software Development
Lecture: Java Platform
Lecturer: Adrian O’Riordan
Course Webpage:
http://www.cs.ucc.ie/~adrian/cs2200.html
Java Programming Language
• Java is an object oriented programming language based on C and
C-based object oriented languages such as C++ and Objective C.
Mesa, Oberon, and Smalltalk were also influences.
• Specifications of the Java language, the Java Virtual Machine (JVM)
and the Java API are community-maintained through the Sunmanaged Java Community Process.
• The Java Runtime Environment (JRE) is the software required to run
any application deployed on the Java platform. End-users commonly
use a JRE in software packages and plugins. Sun distributes a
superset of the JRE called the Java SDK which includes
development tools such as the Java compiler, Javadoc, and
debugger.
Features of Java
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Simple – simpler than C++
Architecture neutral bytecode intermediate format
Object oriented - from the ground up
Portable - standard specification
Distributed - Java platform
High performance - efficient
Multithreaded - built in synchronization primitives
Robust - extensive compile-time checking, followed by a second
level of run-time checking and exception handling
Dynamic - run-time system, classes are linked only as needed
Secure - for networked environments
Web-enabled - Webstart, applets, and servlets
Popular and free - widely used
Tool support – many compilers, supporting IDEs, etc.
Example Feature: Java Garbage Collection
• Basic variables have a predefined duration; objects do not
• JVM manages memory for you - there is no facility to manually
destroy objects in Java
• Java collects “garbage” objects that are no longer needed - objects
that no longer have any references to them
• Un-used objects are not deleted immediately but
– when JVM decides that the amount of free memory is low
– when the program terminates
– when you invoke System.gc()
• Java's use of garbage collection can make Java unsuitable for timecritical applications
• Contrast: C++ programmers have complete control over the
allocation and de-allocation of memory
Java Limitations?
• Look and feel of Swing – default is significantly different from native
apps; new pluggable look and feel system of Swing allows different
looks
• Performance issues – although recent versions significantly faster
than earlier ones and now has JIT compiler
• Not fully object oriented – primitive types are not objects
• Lack of some object oriented features – e.g. operator overloading
and multiple inheritance
• Java was subject to proprietary license – now free software and
open source
Java Timeline I
1994. First made public as Oak programming language developed under
James Gosling at Sun as part of a project codenamed Green. As a
prototype, Patrick Naughton wrote a small web browser, WebRunner, later
renamed HotJava. Oak was renamed Java.
1995. Achieved prominence following the announcement at 1995's SunWorld
that Netscape would be including support for it in their Navigator browser.
1996. Initial release JDK 1.0.
1997 JDK 1.1 Released. Adds inner classes to core language. Also adds Java
Beans, JDBC and RMI
1998. Version 1.2 introduces major changes including Swing graphical API,
This and subsequent releases branded Java 2. JVM has a JIT compiler for
the first time. Collections framework added.
Java Timeline II
2000. J2SE 1.4 released. Adds assert keyword, regular expressions,
and Java WebStart among changes.
2004. Major new release Java 5 (Release 1.5) codename Tiger
introduces a number of new features.
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generics – type safe collections
annotations for metadata
autoboxing- automatic type conversions between promitive types
enumerations – ordered list of values
new for loop iterator syntax
2006 Java SE 6 released. Performance improvements. GUI
improvements
Java Platforms
Sun has defined three platforms targeting different application
environments and segmented many of its APIs so that they belong
to one of the platforms. The platforms are:
– Java Platform, Micro Edition — targeting environments with limited
resources,
– Java Platform, Standard Edition — targeting workstation environments,
and
– Java Platform, Enterprise Edition — targeting large distributed
enterprise or Internet environments.
• The classes in the Java APIs are organized into separate groups
called packages. Each package contains a set of related interfaces,
classes and exceptions.
• Java Platform, Standard Edition or Java SE is a collection of Java
Application Programming Interfaces useful to any Java platform
programs.
Java SE 6 Platform
Java Language
Java Language
Tools &
Tool APIs
java
Security
Deployment
Technologies
User
Interface
Toolkits
JDK
Integration
Libraries
JRE
Other Base
Libraries
javac javadoc apt
Int'l
RMI
jar
Java Web Start
AWT
jconsole
Beans
Intl Support
Networking
Override
Mechanism
Java Plug-in
Swing
Drag n Drop
JDBCTM
IDL
JPDA
IDL Deploy Monitoring Troubleshoot Scripting JVM
TI
Deployment
Accessibility
javap
Input Methods
JNDITM
I/O
Java 2D
Image I/O
RMI
Print Service
RMI-IIOP
JMX
Security Serialization
Sound
Scripting
JNI
Math
Extension
Mechanism
XML JAXP
lang and
Concurrency
Collections
JAR
Logging
Management
lang and util
util
Utilities
Base
Preferences
Regular
Ref Objects Reflection
Versioning Zip Instrument
Libraries
API
Expressions
Java Virtual
Machine
Platforms
Java HotspotTM Client VM
SolarisTM
Linux
Java HotspotTM Server VM
Windows
Other
Ja
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JDK
Programmers can create Java applications using simple tools such as
editors, and command line tools such as provided by Sun’s JDK
(Java SE Development Kit).
Basic tools include:
• javac - compiler for the Java programming language
• java - launcher for Java applications
• javadoc - documentation generator
• appletviewer - run and debug applets
• jar - create and manage Java Archive (JAR) files
• jdb - Java Debugger
Many other tools for e.g. security, networking, monitoring
Java Virtual Machine I
• runtime carries out emulation of the JVM instruction set by
interpreting it; has a stack-based † architecture - each thread has its
own stack and program counter
• each particular host operating system needs its own implementation
of the JVM and runtime.
• verifies all bytecode before it is executed for security reasons designed to allow safe execution of untrusted code from remote
sources as in Java applets - remote code runs in a restricted
sandbox
† a model of computation in which the computer's memory takes the form of
one or more stacks - data structures based on the principle of Last In First
Out (LIFO)
Java Virtual Machine II
HotSpot contains class loader, bytecode interpreter, Client and Server
runtime compilers, garbage collectors, a set of supporting runtime
libraries.
Many JVM implementations, e.g.
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HotSpot (Sun)
Kaffe (open source)
IBM J9 (IBM WebSphere)
IKVM.NET (free)
Apache Harmony (open source)
Exists programming languages for the Java virtual machine aside of
Java itself, e.g. AspectJ, JRuby, Groovy
Important packages
• java.lang - fundamental classes and interfaces closely tied to the
language and runtime system, including the root classes that form
the class hierarchy, types tied to the language definition, basic
exceptions, threading, and security functions; automatically imported
into every source file.
• java.io support for input and output - primarily streams
• java.net - networking including HTTP requests
• java.math - mathematics support
• java.util - data structures and also Scanner class
• java.awt and javax.swing – GUIs
• java.applet – For creation of Web applets
• java.sql – database access
• java.beans – components
• Java.net - networking
Java Libraries
• Core libraries:
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Collection libraries which implement data structures
XML Processing libraries
Security
Internationalization and localization libraries
• Integration libraries, to communicate with external systems:
– Java Database Connectivity (JDBC) for database access
– Java Naming and Directory Interface (JNDI) for lookup and discovery
– RMI and CORBA for distributed application development
• User Interface libraries, which include:
– The (heavyweight, or native) Abstract Windowing Toolkit
– The (lightweight) Swing libraries, which are built on AWT but provide
(non-native) implementations of the AWT widgetry
– Java 2D and APIs for audio capture, processing, and playback
Java Technology Summary
• Development Tools (JDK) – compiling (e.g. javac), running (e.g.
java), documenting (javadoc), debugging (jdb)
• APIs (Application Programming Interface) – library specs
• Deployment Technology – applications, applets, JAR files, Web
Start, plug-ins
• User Interface and Graphics Toolkits – Swing, AWT, Java 2D
• Integration Libraries – JDBC – database connect, Java RMI
• Components, Enterprise Java – JavaBeans, Servlets, J2EE
Applets, Servlets and Java Web Start
• Applets
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included in an HTML page - <APPLET> tag
run in Web browser (requires a plugin) or JDK’s AppletViewer
in Java since the beginning
Used to provide interactive features to webpages
• Servlets
– Java Servlet allows addition of dynamic content to a Web server
– JavaServer Pages (JSP) allows dynamic generation of HTML, XML or
other types of documents in response to a Web client request
• Java Web Start
– started directly from the Internet using a web browser but do not run in
the browser
Web refs
• Java Beginnings – Early years at Sun
• Java History – Feizabadi
• 1996 White Paper
• Java@Sun
• Java Community Process
• Java SE
• Java EE
• java.net Portal