import java.io.*;

/**
 * Project #5.1
 * 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 FileDisplay
{
   /**
    * 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
   {
      String fileName;
      
      /* 1. Read the command line arguments for a file name, if no filename
        *    is given, then ask for one.
        */
      if (args.length == 0)
      {
         System.out.println("This program displays a file specified by"
            + " a command line argument.");
         System.out.println("You didn't specify a filename,"
            + " so please enter one now.\n");
            fileName = inputFilename();
      }
      else
      {
         fileName = args[0];
      }
        
      // 2. Display the file to the screen.
      displayFile(fileName);
   }
    
    
   /**
    * Queries the user for a file name.
    * <P>
    * @return    The filename input by the user
    */
   public static String inputFilename() throws IOException
   {
      // 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.
      String fileName = userReader.readLine();
      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
   {
      // Open the file for reading.
      BufferedReader buffReader = openFile(fileName);
        
      // Read in each line and display it.
      String line;
      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);
        
      // Wrap the FileReader with a BufferedReader for ease of use.
      BufferedReader buffReader = new BufferedReader(fileReader);
      return buffReader;
   }
} // End class FileDisplay