Programming in Java

1
Programming in Java

• Review Topics for Further Study

2
Course Review (1)

• Introduction
• Basic structure of a Java application
• Java applets
• Java as a programming language
• data types
• type casting
• variables, operators, expressions
• statements (if, while, do, )
• input and output
• comparison to C/C
• Arrays (single multidimensional)
• String, StringBuffer, StringTokenizer

3
Course Review (2)

• Object-oriented programming in Java
• Classes, objects
• Defining custom classes and methods
• Private, protected, package, and public
  visibility of classes and members
• Instance members vs. class members (variables
  methods)
• Method overloading
• Java's inheritance model
• inheritance hierarchy
• use of interfaces to simulate multiple
  inheritance
• abstract classes
• Packages

4
Course Review (3)

• Graphics Primitives
• Color
• Lines, ovals, rectangles, etc.
• Graphical User Interfaces
• GUI components (Buttons, Text Fields, Labels, )
• Event-driven programming
• Containers
• Component hierarchies
• Layout managers
• Exception Handling
• try, throw, catch, finally
• Threads

5
There's much more to Java!

• This course barely scratched the surface!
• Java
• 1.0 8 packages, 211 classes
• 1.1 23 packages, 503 classes
• 1.2 Expected to be released summer 1998 will be
  much larger
• Remaining slides briefly look at a few other
  topics

6
Object Serialization

• Serialization - Writing objects to a file
• Deserialization - Reading objects from a file
• Example Declaration
• class Point implements Serializable
• public int x
• public int y
• Point (int ax, int ay) xax yay
• public String toString() return
  "("x","y") "
• class Line implements Serializable
• public Point p1, p2
• Line (Point ap1, Point ap2) p1ap1 p2ap2
• public String toString() return p1 "-"
  p2

7
Object Serialization

• class LineWriter
• public static void main(String args) throws
  IOException
• / Set up object to be serialized /
• Line l new Line (new Point (1,2), new Point
  (3,4))
• System.out.println ("Line " l)
• / Set up the ObjectOutputStream /
• FileOutputStream fos new FileOutputStream
  ("deleteme.akm")
• GZIPOutputStream gzos new
  GZIPOutputStream(fos)
• ObjectOutputStream out new
  ObjectOutputStream(gzos)
• / Write out the object and clean up /
• out.writeObject(l)
• out.flush()
• out.close()

8
Object Deserialization

• class LineReader
• public static void main (String args)
• throws IOException, ClassNotFoundException
• / Setup the reader /
• InputStream fis new FileInputStream
  ("deleteme.akm")
• GZIPInputStream gzis new GZIPInputStream
  (fis)
• ObjectInputStream in new ObjectInputStream(g
  zis)
• / Read the object /
• Line l (Line) in.readObject()
• System.out.println ("Line " l)

9
Java Beans

• A reusable software component that can be
  manipulated visually in a builder tool
• Examples
• Spreadsheet Graph generator module Telephony
• Java's version of Active-X (OCX, OLE)
• Language independent Reusable components
• Standard specifications for accessing properties
  and methods

Java Bean
Application Program
Beanbox tools
10
Internationalization (I18N)

• Internationalization
• Process of making a program flexible enough to
  run in any locale
• Localization
• Process of arranging for a program to run in a
  specific locale
• java.util.Locale
• Characters
• Unicode char encoding (16 bit) allows multiple
  alphabets
• InputStreamReader, OutputStreamWriter - convert
  local encoding to Unicode.
• Dates, times, formatting numbers, money, sorting
  strings
• java.text package addresses these
• See /jdk1.1.5/demo/i18n/DateTimeFormat
• Text messages should be displayed in the local
  language
• ResourceBundle (and related classes in java.util)
  facilitates this.

11
Reflection

• Reflection
• Can be used to obtain information about a class
  and its members (properties, events, methods)
• Can get/set values of instance variables
  dynamically
• Can invoke methods dynamically
• Technique is used by JavaBeans "introspection"
  mechanism
• Implemented in the package java.lang.reflect
• Example
• JIN examples/ch12/ShowClass.java

12
Database Access with SQL

• JDBC
• Java DataBase Connectivity
• Allows Java programs to send SQL queries to
  database servers
• Implemented by classes in the package java.sql
• An API interface (not embedded SQL)
• Example statements (not complete!)
• import java.sql.
• // Get database url, userid, password, establish
  connection
• Connection conn DriverManager.getConnection(url,
  usr,pwd)
• Statement s conn.createStatement()
• try
• s.executeUpdate("CREATE TABLE POINT (x INT, y
  INT)")
• catch (SQLException e)

13
Remote Method Invocation

• Remote Method Invocation (RMI)
• Powerful technology for networked applications
• Server defines objects that clients can use
  remotely
• Clients invoke methods of the objects remotely
• Arguments and return values
• Can be primitive values or Serializable objects
• Server and client must be Java applications
• Implemented using packages java.rmi and
  java.rmi.server

14
Networking (URL)

• Part of package java.net (classes for networking)
• URL Uniform Resource Locator
• Class Organizes manipulation of URLs
• Example Display contents of a (text) URL
• import java.io.
• import java.net.
• public class AkmGetURL
• public static void main(String args) throws
  IOException
• URL url new URL("filec/autoexec.bat")
• InputStream in url.openStream()
• // Now copy bytes from the URL to the output
  stream
• byte buffer new byte4096
• int bytes_read
• while((bytes_read in.read(buffer)) ! -1)
• System.out.write(buffer, 0, bytes_read)
• in.close()

15
Networking (URLConnection)

• URLConnection
• Allows you to get information about URL
  documents
• import java.io.
• import java.net.
• public class AkmGetURL
• public static void main(String args) throws
  IOException
• URL url new URL(args0)
• URLConnection con url.openConnection()
• System.out.println ("Encoding "
  con.getContentEncoding())
• System.out.println ("Length "
  con.getContentLength())
• System.out.println ("Type "
  con.getContentType())
• System.out.println ("Expires "
  con.getExpiration())
• System.out.println ("Modified "
  con.getLastModified())

16
Networking (getContent)

• import java.io.
• import java.net.
• public class AkmGetURL
• public static void main(String args) throws
  IOException
• URL url new URL(args0)
• Object urlContent url.getContent()
• System.out.println (" getContent returned
  instance of "
• "class "
  urlContent.getClass())
• System.out.println ("----------Content--------
  ---")
• if (urlContent instanceof String)
• System.out.println (urlContent)
• else if (urlContent instanceof InputStream)
  
• InputStream is (InputStream) urlContent
• int b is.read()
• while (b!-1) System.out.print((char) b)
  bis.read()
• System.out.print("\n")
• else
• System.out.println ("Cannot show object of
  this type")

17
Sockets

• Sockets
• Streams of data that can flow between networked
  computers
• Involves at least two programs
• Server supplies data and services
• Client requests data and services
• "EchoServer"
• Example of Client/Server socket communication
• Client sends text Strings to server
• Server converts the strings to upper case and
  returns them
• Note
• To keep things simple, no error checking is done
• Should have "try catch" blocks to check for
  disconnect, etc.
• To allow multiple clients, should use threads
  (each client gets its own thread

18
EchoServer
Server
out
in
in
out
Client
19
EchoServer

• import java.net.
• import java.io.
• public class EchoServer
• public static void main(String args) throws
  IOException
• int thePort 1234
• ServerSocket theServerSocket new
  ServerSocket(thePort)
• System.out.println( "Server ready." )
• Socket theSocket theServerSocket.accept()
  // Accept client
• System.out.println( "Client connected." )
• / Establish socket in/out streams /
• BufferedReader in new BufferedReader
• (new InputStreamReader(theSocket.getInputStr
  eam()))
• PrintWriter out new PrintWriter
• (new OutputStreamWriter(theSocket.getOutputS
  tream()), true)

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EchoServer (cont)

• / Service requests /
• while (true)
• String line in.readLine()
• if (line null) break
• System.out.println("Read " line)
• line line.toUpperCase() "!"
• out.println(line)
• System.out.println("Wrote " line)
• / Clean up and exit /
• in.close()
• out.close()
• theSocket.close()
• theServerSocket.close()

21
EchoClient (1)

• // A client applet (works with EchoServer.java)
• import java.awt.
• import java.awt.event.
• import java.applet.
• import java.net.
• import java.io.
• public class EchoClient extends Applet
• final static int thePort 1234
• BufferedReader in
• PrintWriter out
• TextField theField new TextField(20)
• TextArea theArea new TextArea()

22
EchoClient (2)

• public void init()
• try
• String host getCodeBase().getHost()
• Socket theSocket new Socket( host,
  thePort )
• in new BufferedReader
• (new InputStreamReader(theSocket.getInputSt
  ream()))
• out new PrintWriter
• (new OutputStreamWriter(theSocket.getOutputStre
  am()), true)
• add(theField)
• add(theArea)
• setVisible(true)
• theField.addActionListener(new
  ActionListener ()
• public void actionPerformed(ActionEvent
  theEvent)
• out.println( theField.getText() )
• theField.setText( "" )
• )
• catch (IOException io)

23
EchoClient (3)

• public void start()
• try
• while (true)
• String s in.readLine()
• if ( s ! null ) theArea.append( s '\n' )
• catch (IOException io)
• System.err.println( "IOException\n" io
  )

24
Swing

• A new GUI toolkit
• Will be part of JDK1.2 - Swing is already
  released separately
• Simplifies development of windowing components
• Customizable "look and feel"
• Menus, tabs, controls look like those of a
  "native" application
• Or, you can give your application a specific look
  and feel for a specific target platform

25
Heavyweight vs. Lightweight

• Extends AWT
• All AWT components are heavyweight
• All Swing components are lightweight (except
  JWindow, JFrame, JDialog, and JApplet)
• Mixing Heavyweight and Lightweight components is
  not recommended
• Lightweight components
• More efficient use of resources
• More consistent across platforms
• Cleaner LF integration (more control over this)
• Can have transparent pixels
• Can be non-rectangular
• Don't respond to mouse events (they fall through
  to parent)
• Swing has many more UI components than AWT
• Tree-view, list-box, tabbed-pane
• Adhere to JavaBeans specifications

26
Swing is part of JFC 1.2

• JFC 1.2 contains three major APIs
• Java 2D - Set of classes for advanced 2D graphics
  and imaging
• Drag and Drop - Enables data transfer
• Between Java application and native application
• Across Java Applications
• Within a single application
• Accessibility API - Provides assistive
  technologies
• Examples screen magnifiers and audible text
  readers
• Designed to help people with disabilities
  interact with JFC and AWT components