User Interfaces File I/O and Exceptions

User Interfaces File I/O and Exceptions (c) IDMS/SQL News http://www.geocities.com/idmssql

User Interfaces • In Java one can create at least 3 types of programs Applet Servlet Windows Java Class A fourth can be applications run from Command Prompt (=DOS) File I/O Simple Example (c)http://www.geocities.com/idmssql

Different User Interfaces • User interface can vary depending upon code execution is at client or server side • Here we take the simplest case of File I/O at the client side • Programs will be run from the command prompt (=dos window) File I/O Simple Example (c)http://www.geocities.com/idmssql

I/O - File Based in Java • We have already seen one form of output – print statement • System.out.print(“Hello Printer”); • In reality we are using the print method of the class PrintStream • System.out is an instance of the class PrintStream • Note: see http://java.sun.com/j2se/1.3/docs/api/java/io/PrintStream.html File I/O Simple Example (c)http://www.geocities.com/idmssql

Output file • We can define a file using class called FileOutputStream and PrintStream of package java.io • FileOutputStream fout= new FileOutputStream ("Writef1.out"); • PrintStream myOutput = new PrintStream(fout); • Now one can write to the file “Write1.out” using myOutput.print commands! File I/O Simple Example (c)http://www.geocities.com/idmssql

import java.io.*; // Class definition and implementation. public class Writef1 { public static void main (String args[]) { try { FileOutputStream fout= new FileOutputStream ("Writef1.out"); PrintStream myOutput = new PrintStream(fout); if (args.length == 0) { myOutput.println("Hello Nobody "); myOutput.println("Try with some arguments ");} else { for (int i=0; i < args.length; i = i+1) { myOutput.println(args[i]);}} } // try ends here catch (IOException e) { System.out.println("Error=" + e); System.exit(1); } // end of catch } } File I/O Simple Example (c)http://www.geocities.com/idmssql

Exceptions • try and catch statements • Try { code} catch (exception_type xyz1) { code to process this ...} • There can be multiple catch blocks • like our ”call IDMS-STATUS”! • When doing file I/O exception must be coded • Note: There are other ways to handle exceptions in Java like a method throws ....xyzException etc File I/O Simple Example (c)http://www.geocities.com/idmssql

Exception Example Code class Except1 { public static void main (String args[]) { int i = 0; String [] greetings = { " Merry Christmas", " God Jul ", " Hyvää Joulua"}; try{ for (i=0; i < 4; i = i+1) { System.out.println(greetings[i]);} } // end of try catch (ArrayIndexOutOfBoundsException e ) { System.out.println(" --------------------------"); System.out.println(" Check Index Variable Value"); System.out.println(" --------------------------");} }} File I/O Simple Example (c)http://www.geocities.com/idmssql

User Interfaces File I/O and Exceptions