Programming in Java

1. Programming in Java Review; Topics for Further Study Programming in Java; Instructor:Alok Mehta 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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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) { x=ax; y=ay; } • public String toString() { return "("+x+","+y+") "; } • } • class Line implements Serializable { • public Point p1, p2; • Line (Point ap1, Point ap2) { p1=ap1; p2=ap2; } • public String toString() { return p1 + "-" + p2; } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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(); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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(gzis); • /* Read the object */ • Line l = (Line) in.readObject(); • System.out.println ("Line: " + l); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Application Program Java Bean Beanbox tools Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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. Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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) { • … • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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("file:c:/autoexec.bat"); • InputStream in = url.openStream(); • // Now copy bytes from the URL to the output stream • byte[] buffer = new byte[4096]; • int bytes_read; • while((bytes_read = in.read(buffer)) != -1) • System.out.write(buffer, 0, bytes_read); • in.close(); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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(args[0]); • 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()); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

16. Networking (getContent) • import java.io.*; • import java.net.*; • public class AkmGetURL { • public static void main(String[] args) throws IOException{ • URL url = new URL(args[0]); • 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); b=is.read(); } • System.out.print("\n"); • } else { • System.out.println ("Cannot show object of this type"); • } • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

18. EchoServer Server out in out in Client Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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.getInputStream())); • PrintWriter out = new PrintWriter • (new OutputStreamWriter(theSocket.getOutputStream()), true); Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

20. 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(); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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(); Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

22. EchoClient (2) • public void init() { • try { • String host = getCodeBase().getHost(); • Socket theSocket = new Socket( host, thePort ); • in = new BufferedReader • (new InputStreamReader(theSocket.getInputStream())); • out = new PrintWriter • (new OutputStreamWriter(theSocket.getOutputStream()), 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) { • System.err.println("IOException:\n" + io); • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 ); • } • } • } Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 L&F 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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study

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 Programming in Java; Instructor:Alok Mehta Review; Topics for Further Study