Scanner and JFileChooser

By: Nicholas Duchon

Outline:

Mac Issues

JFileChooser has some issues on a Mac when the program is creating a complex GUI as part of the constructor and JFileChooser is supposed to show before the GUI.
Here are three ways to fix this problem (I think). The problem is actually hard to reproduce with relatively simple GUI's:
public static void main(String[] args) throws Exception {
  // an approach using javax with lambda expressions
     javax.swing.SwingUtilities.invokeLater (() -> new Program());
  // an approach using java with lambda expressions
     java.awt.EventQueue.invokeAndWait (() -> new Program());
  // an approach using an anonymous inner class
     java.awt.EventQueue.invokeAndWait (
       new Runnable() {
         @Override
           public void run() {
             new Program();
           } // end run method
       } // end inner class definition
     ); // end invokeAndWait method.
} // end method main

JFileChooser

Here's an example using JFileChooser:

// File: ChooserExample.java
// Date: Apr 30, 2010
// Author: Nicholas Duchon
// Purpose: Demonstrate JFileChooser
//    reading a file with Scanner
//    starting chooser in current directory

 import java.io.FileNotFoundException;
 import javax.swing.JFileChooser;
 import javax.swing.JOptionPane;
 import java.util.Scanner;

 public class ChooserExample {
    public static void main (String args []) {
       // sometimes starting with JFileChooser can be erratic,
       // so the following seems to be a reliable way to start:
       JOptionPane.showMessageDialog(null, "Welcome.\nBy: Nicholas Duchon\nOct 12, 2017");
       // start the search in the current directory
       JFileChooser chooser = new JFileChooser(".");
       int returnVal = chooser.showOpenDialog(null);
       if(returnVal == JFileChooser.APPROVE_OPTION) {
          System.out.println("You chose to open this file: " +
             chooser.getSelectedFile().getName());
          // open and read file:
          try {
             Scanner sfin = new Scanner (chooser.getSelectedFile()); // NOT the file name!!!!
             while (sfin.hasNext())
                System.out.println (sfin.nextLine());
          }
             catch (FileNotFoundException e) {
                JOptionPane.showMessageDialog(null, "File not found.");
             } // end try/catch
       } // end if file chosen
    } // end main
 } // end file ChooserExample

Pestering

Here's some very simple code to open a file, pestering the user until the open succeeds.

NOTE: The "FileNotFoundException" is thrown by the Scanner constructor, NOT by the File constructor!

import java.util.Scanner;
import java.io.FileNotFoundException;
import java.io.File;

public class GetFile {
  public static void main (String args []) {
    Scanner sin = new Scanner (System.in);
    Scanner fin = null;
    String fname = "";

    while (fin == null) {
      System.out.print ("File name: ");
      fname = sin.next(); // get file name
      try {
        fin = new Scanner (new File (fname));
      } catch (FileNotFoundException e) {
        System.out.println ("File not found: " + fname);
      }
    } // end until good file found

    System.out.println ("File open ok: " + fname);
  } // end main

} // end class GetFile

Filtering

Example using JFileChooser with file name extension filtering
// File: ChooserExample.java
// Date: Apr 30, 2010
// Author: Nicholas Duchon
// Purpose: Demonstrate JFileChooser
//    reading a file with Scanner
//    starting chooser in current directory


   import java.io.FileNotFoundException;
   import javax.swing.JFileChooser;
   import javax.swing.filechooser.FileNameExtensionFilter;
   import javax.swing.JOptionPane;
   import java.util.Scanner;


   public class ChooserExample {
      public static void main (String args []) {
         Scanner sfin = getScanner (); // call method to select and open file
         while (sfin.hasNext()) 
            System.out.println (sfin.nextLine());
      } // end main
    
      public static Scanner getScanner () {
       // start the search in the current directory
         JFileChooser chooser = new JFileChooser("."); // Start selection at dot!

         FileNameExtensionFilter filter;
         filter = new FileNameExtensionFilter("txt", "txt");
         chooser.setFileFilter(filter);
         chooser.addChoosableFileFilter (new FileNameExtensionFilter("java", "java"));
         chooser.addChoosableFileFilter (new FileNameExtensionFilter("txt, java and class", "txt", "java", "class"));
      
         int returnVal = chooser.showOpenDialog(null);
         if(returnVal == JFileChooser.APPROVE_OPTION) {
            System.out.println("You chose to open this file: " +
               chooser.getSelectedFile().getName());
          // attach Scanner to open and read file:
            try {
               return new Scanner (chooser.getSelectedFile());
            } 
               catch (FileNotFoundException e) {
                  JOptionPane.showMessageDialog(null, "File not found.");
               } // end try/catch
         } // end if file chosen
         return null;
      } // end method getScanner
   
   } // end file ChooserExample

Delimiters

Using regular expressions to define delimiters in Scanners:

ND.