The Java 2SE Platform

1
The Java 2SE Platform

• Lars Degerstedt
• Linköping university, IDA
• larde_at_ida.liu.se

2
This Lecture

• 1st hour Java, the language
• Prelimiaries Java 2 overview
• Language constructs
• Java programs
• 2nd hour Java, APIs
• Literature
• The Java Tutorial http//java.sun.com/docs/books/t
  utorial

3
Preliminaries UML and objects
Interface
Class/Superclass
Eater
Animal
size int
getFood() Food
BodyParts List
getFood() Food
Consists of
Leg
inherits
Dog
Subclass
4
The Java 2 Platform and J2SE

• Several parts Language, JVM, APIs, Component
  models, and still growingall packages in
  subplatforms.
• Our main focus J2SE Java 2 Standard Edition

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The Java Language (SDK 1.4)

• Almost pure object-oriented
• Static methods/fields, e.g. the main method
• Single inheritance
• Interfaces and classes
• Runs interpreted on Java Virtual Machine (JVM)
  everywhere, not always true
• graphical components have problems
• Different machines JVM/KVM
• Garbage collection explicit call
  java.lang.System.gc()

6
Example Java Class brief

• import java.io.
• import java.net.URL
• package java.being.primates
• public class Dog extends Animal implements
• Eater
• private int size -1
• private Food food null
• public Dog(int size, Food food)
• this.size size
• this.food food
• public Food getFood()
• return food

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Variables

• Static typing (almost, see inner classes)
• int zero 0
• public String enStrang nisse
• Casting
• String s (String) anObject

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Data Types

• Primitive
• byte,short, int, long
• float double
• char
• Boolean
• Reference
• Objects
• arrays

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Operators

• Arithmetic - / , --
• Relational gt , gt, lt, lt, , !
• Conditional , , !, , ,
• Assignment - /
• Others .(Type)new instanceof this super
• Blocks
• Scope is block dependent

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Control Flow Statements

• looping while, dowhile , for
• Branching ifelse, switchcase
• Exceptions trycatchfinally,throw, throws
• aborts break, continue, label, return

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Java programs

• Executable programs are collections of
  classes/interfaces that
• Compiles, i.e. No dangling references
• Contains a main method
• static void main(String args)
• Jar-archives optional encapsulation of compiled
  classes, e.g.
• mylib.jar

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Compiling/ Running Programs

• javac MyClass.java
• -gt MyClass.class
• java MyClass
• Starts and runs program
• Start point
• public class MyClass
• public static void main(String argv)
  

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CLASSPATH

• To link in external classes
• Win
• java classpath c\myJavac\jars\myjar.jar
  MyClass.java
• Solaris
• java classpath /home/my/myJava/home/my/myjar.jar
  MyClass.java

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Classes

• Blueprint of objects (state and behavior)
• One top level class one file
• Default inheritance from java.lang.Object
• Modifiers
• public, protected, private
• abstract, final

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Interfaces

• Abstract Class definition
• A set of methods for a class type
• Class type description
• Multiple views on Class
• Class contract
• Can also declare constants
• Two uses
• Callback making methods parameters
• Polymorphism alternative to subclasses

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Methods

• Methods that provide behavior for Classes
• In Parameters
• Fixed number use anonymous arrays for dynamic
  case
• Return Value (return statement/type)
• Single object/primitive/array
• Modifiers
• public, protected, private
• static, final, native, synchronized

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Constructors

• Method that initialize objects
• Default constructor
• Constructors are not inherited
• Modifiers
• public, protected, private

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Fields

• Primitives and Classes
• Must have a type
• All Fields are objects in reality
• Even primitives
• Modifiers
• public, protected, private
• static, final, transient, volatile

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Packages Import

• Packages are namespaces for groups of Classes
• ex java.lang
• protected modifier
• used to be usable in package and for subclasses
• Packages can be imported
• to use Classes by short Name
• e.g String vs. java.lang.String

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Example Class again

• import java.io.
• import java.net.URL
• package java.being.primates
• public class Dog extends Animal implements
• Eater
• private int size -1
• private Food food null
• public Dog(int size, Food food)
• this.size size
• this.food food
• public Food getFood()
• return food

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Naming Conventions

• Classes
• MyClassName
• Methods
• myMethodName()
• Variables
• MyClass myClass new MyClass()
• Packages
• java.lang, opennlp.jbrickslib.util

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System

• java.lang.System
• System.out, System.in
• java.lang.RunTime
• java.lang.Process, java.lang.SecurityManager
• java.lang.Object
• java.lang.Class, java.langClassLoader
• Integer, Byte, Boolean, Char, String,
  StringBuffer, Double

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Comments

• // on liners
• / Multi linersexpanding several lines/
• /Javadoc comment/

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Javadoc

• Document generation based on _at_-tags and automated
  code extraction
• /
• Class description goes here.
• _at_version 1.82 18 Mar 1999
• _at_author Firstname Lastname
• /
• public class Blah extends SomeClass

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Unicode

• Java character encoding
• The Unicode Standard, Version 2.0, ISBN
  0-201-48345-9
• A unique number for every character
• no matter platform, program, language

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This Lecture

• 1st hour Java, the language
• 2nd hour Java, APIs
• Overview of J2SE APIs
• Collections
• Graphics AWT/Swing
• Reflection
• XML
• JDBC

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J2SE (v1.4) APIs - Overview
User Interface toolkits
Swing
AWT
Input methods
Sound
Java2D
Access
Integration APIs
RMI
JDBC
JNDI
CORBA
Core APIs
XML
Logging
Beans
Locale
Pref
Collections
JNI
Security
Lang
Util
New I/O
Network
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Collection/Map API

• Representing and manipulating collections/maps
• Collections have three parts
• Interfaces ADT APIs
• Implementations data structures
• Algorithms polymorphism
• Program with interfaces
• List l new ArrayList()
• Interoperatibility beyond vectors
• Fosters software reuse
• element and bulk operations add/addAll

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Collection/Map Interface Taxonomy
AbstractCollection
AbstractMap
HashMap
AbstractSet
TreeMap
AbstractList
HashSet
ArrayList
TreeSet
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Collection/Map Collections

• Group of elements (e.g. List or Set)
• Add/Remove/Iterate/Contains
• Bulk operations are polymorphic, i.e. works on
  any Collection
• Parameter for Map interface
• toArray method for export

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Collection/Map Lists

• Positional access
• Arrays.toList() method for static list view of
  array
• ListIterator allows for manipulation during
  iteration
• Sublist extraction

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Collection/Map Maps

• Collection views of keys and values
• Iterators over keys, values, and tuples
• Bulk op. putAll imports maps
• Equals must imply hashCode for elements
• Bulk op. retainAll restricts a map to a given
  Collection

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Graphics are Components

• AWT and Swing is based on Components and
  Containers
• Components are placed in containers
• update(), paint(), repaint()
• Layout Managers
• Swing is now the pushed Window Toolkit from SUN

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Graphics AWT Hierarchy
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Graphics AWT Event Model

• Messaging across Java classes
• java.awt.event (extended in javax.swing.event)
• Event listener
• the Observer Design pattern
• Interested classes report them selves to event
  casting classes

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Graphics AWT-Example Event

• import java.awt.
• import java.awt.event.
• class MyApp implements ActionListener Button
  okButton new Button()
• MyApp()
• // build graphics components
• okButton new Button(OK)
• okButton.addActionListener(this)
• // deploy gui widget
• public void actionPerformed(ActionEvent e)
  System.out.println(Hey, you pressed
  OK button!")

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Graphics Swing

• Two types of entities
• atomic components and containers
• More advanced Window Toolkit
• but uses the AWT event model
• Control-View-Model design pattern
• gui-state and application-data models. Ex
  Button, table resp.
• Text parsing (HTML)
• No native code lightweight
• AWT and Swing components dont mix!

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Swing Containment hierarchy
The Containment hierarchy
OBS!
Containment is a dynamic Property not the
taxonomy
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Swing Code Example
public static void main(String args) try
UIManager.setLookAndFeel(UIManager.getCrossPlatf
ormLookAndFeelClassName()) catch (Exception
e) JButton button new JButton("I'm a Swing
button!") button.setMnemonic(KeyEvent.VK_I)
button.addActionListener(...create an action
listener...) labelPrefix "Number of button
clicks " numClicks 0 label new
JLabel(labelPrefix "0 ") JPanel pane new
JPanel() pane.setBorder(BorderFactory.createEmpt
yBorder(30, 30, 10, 30)) pane.setLayout(new
GridLayout(0, 1)) pane.add(button)
pane.add(label) JFrame frame new
JFrame("SwingApplication") frame.getContentPane(
).add(pane, BorderLayout.CENTER)
frame.addWindowListener(...) frame.pack()
frame.setVisible(true)
Obs
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Swing Containers

• Containers arrange collections of visual Swing
  components
• Top level containers JFrame, JDialog, JApplet
• Intermediate containers/Content panes JPanel,
  JLayeredPanel, JInternalFrame, JScrollPane, etc.

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Swing Component/Container Taxonomy
Container
AWT
JComponent
Window
Frame
AbstractButton
JPanel
Swing
JButton
JFrame
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AWT/Swing Layout Managers

• Objectified functionality of Container
• Both AWT and Swing have managers

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AWT/Swing Implementation

• AWT is heavyweight have platform-specific peer
  classes.
• Swing is lightweight uses AWT, thus only
  indirectly related to underlying platform.
• Swing has pluggable Look and Feel
• Event dispatching thread AWT/Swing is
  single-threaded.
• Use SwingUtilities for threads invokeAndWait,
  invokeLater

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Graphics Additional Features

• Drag and Drop
• Internationalization
• Adapting to various languages and regions without
  engineering changes
• Accessibility
• Support for People with Disabilities
• Java Foundation Classes (JFC) bean support
  (ready for drag and drop)

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XML

• Java to XML
• Save Java classes in XML (JAXB)
• XML-Remote Procedure Call (like SOAP)
• XML messaging...
• Working with XML documents
• XML parser
• DOM navigation (eg JAXP)
• XML Binding (saving Java to XML)

JAXP API
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Reflection Java meta-programming

• Inspection of objects (both arrays and classes)
• Superclasses
• The Class object
• Method and Field objects
• Meta-creation of new objects
• Meta-evaluation of methods/fields
• Security and exception handling somewhat elaborate

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JDBC

• Java Data Base Connectivity
• High-level API to SQL-databases
• java.sql.
• Includes network connection
• Vendor specific Drivers take care of networking
  and DB-connections

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JDBC Accessing the Database
Java Client
java.sql.Connection
Creates
Database
Java.sql.Statement
SQL Call API

• Load Driver
• Create a connection
• Create Statement and execute SQL-commands
• Extract Results
• Close connection

Creates
Java.sql.Resultset
SQL Result API
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JDBC Code Example

• Class.forName(com.mysql.jdbc.Driver).newInstance
  ()
• String url jdbcmysql//maj4.ida.liu.sebird_da
  tabase
• Connection c DriverManager.getConnection(url,
  "my_login", "my_password")
• Statement stmt con.createStatement()
• Resultset rs stmt.executeQuery(SELECT FROM
  species WHERE name \skata\")
• rs.next()
• String text rs.getString(migration_field)
• System.out.println(Skata has migrationtext)

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Java News

• Java 2SE, version 1.5
• Language extensions, e.g. Parameterized types
• New APIs, e.g. java.util.concurrent
• Suns Java Desktop System
• Java-based graphical desktop on top of
  Linux/GNOME
• Java Community Process
• Future enhancements of the Java Platform