import java.io.*;

/**
 * Project #5.3
 * CS 2334, Section 001
 * Sept 23, 2002
 * <P>
 * This classs implements a program that shows how Exceptions work.
 * </P>
 * @author unknown
 * @version 1.0
 */
public class FileDisplay3
{
   /**
    * This is the main method for this test program. Since this is a
    * simple test program, all of our code will be in the main method.
    * Typically this would be a bad design, but we are just testing out
    * some features of Java.
    * <P>
    * Algorithm<br>
    * 1. Read the command line arguments for a file name, if no filename
    *    is given, then ask for one.
    * 2. Display the file to the screen.
    * </P>
    * @param             args       Contains the command line arguments.
    */
   public static void main(String args[]) throws IOException
   {
      // Variables
      String fileName="";
        
      /* If there are command line arguments, the first one
        * should be the file name.
        */
      if (args.length >= 1)
      {    
         fileName = args[0];
      }
        
      // Display the file to the screen.
      boolean redo = false;
        
      do
      {
          try
          {
             displayFile(fileName);
             // If we get here, opening the file was successful!
             redo = false;
          }
          catch(IOException ioe)
          {
             fileName = inputFilename();
             /* If we get here, opening the file was NOT successful.
              * Therefore, we must try displaying the file again,
              * since it didn't work the first time.
              */
             redo = true;
          }
      }
      while (redo);
   }
    
   /**
     * Queries the user for a file name.
     * <P>
     * @return    The filename input by the user
     */
   public static String inputFilename() throws IOException
   {
      String fileName = "-1";
        
      // Print a friendly message requesting a filename.
      System.out.print("Please enter a file name: ");
        
      // Use a BufferedReader to get user input.
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader userReader = new BufferedReader(isr);
        
      // Read a line of text from the user.
      try
      {
         fileName = userReader.readLine();
      }
      catch(IOException ioe)
      {
         System.out.println("Cannot read from BufferedReader");
         System.exit(1);
      }
      
      return fileName;
   }
    
    
   /**
    * Displays the contents of the given file to the screen.
    * <P>
    * @param   fileName         The name of the file to display.
    * @throws  IOException      Thrown if there is an error displaying the file.
    */
   public static void displayFile(String fileName) throws IOException
   {
      String line;
      
      // Open the file for reading.
      BufferedReader buffReader = openFile(fileName);
        
      // Read in each line and display it.
      while((line = buffReader.readLine()) != null)
      {
         System.out.println(line);
      }// null signifies End-of-File.
      
      buffReader.close();
   }
    
    
   /**
    * Opens the file and creates a BufferedReader for it.
    * <P>
    * @param    fileName        The file to be opened.
    * @return                   A BufferedReader to read from the specified file
    * @throws   IOException     Thrown if there is an error opening the file
    */
   public static BufferedReader openFile(String fileName) throws IOException
   {
      // Open the file using a FileReader.
      FileReader     fileReader = new FileReader(fileName);
      BufferedReader buffReader = new BufferedReader(fileReader);
  
      return buffReader;
   }
} // End class FileDisplay3