Using File listFiles with FileNameExtensionFilter

Question

I would like to get a list of files with a specific extension in a directory  In the API  Java 6   I see a method File listFiles FileFilter  which would do this   Since I need a specific extension  I created a FileNameExtensionFilter  However I get a compilation error when I use listFiles with this  I assumed that since FileNameExtensionFilter implements FileFilter  I should be able to do this  Code follows   FileNameExtensionFilter filter   new FileNameExtensionFilter  text only   txt    String dir      users blah dirname   File f      new File dir   listFiles filter     The last line shows a compilation error      method listFiles FileNameFilter  in type File is not applicable for arguments of type FileNameExtensionFilter   I am trying to use listFiles FileFilter   not listFiles FileNameFilter   Why does the compiler not recognize this   This works if I write my own extension filter extending FileFilter  I would rather use FileNameExtensionFilter than write my own  What am I doing wrong

User · Answer

Here s something I quickly just made and it should perform far better than File getName   endsWith   xxxx     import java io File  import java io FileFilter   public class ExtensionsFilter implements FileFilter        private char     extensions       private ExtensionsFilter String   extensions                int length   extensions length          this extensions   new char length             for  String s   extensions                        this extensions --length    s toCharArray                          Override     public boolean accept File file                char   path   file getPath   toCharArray            for  char   extension   extensions                        if  extension length  gt  path length                                continue                            int pStart   path length - 1              int eStart   extension length - 1              boolean success   true              for  int i   0  i  lt   eStart  i                                  if   path pStart - i    0x20      extension eStart - i    0x20                                         success   false                      break                                              if  success                  return true                    return false            Here s an example for various images formats   private static final ExtensionsFilter IMAGE FILTER          new ExtensionsFilter new String      png     jpg     bmp

User · Answer

With java lambdas  available since java 8  you can simply convert javax swing filechooser FileFilter to java io FileFilter in one line   javax swing filechooser FileFilter swingFilter   new FileNameExtensionFilter  jpeg files    jpeg    java io FileFilter ioFilter   file - gt  swingFilter accept file   new File  myDirectory   listFiles ioFilter

User · Answer

The FileNameExtensionFilter class is intended for Swing to be used in a JFileChooser   Try using a FilenameFilter instead  For example   File dir   new File   users blah dirname    File   files   dir listFiles new FilenameFilter         public boolean accept File dir  String name            return name toLowerCase   endsWith   txt

User · Answer

Duh     listFiles requires java io FileFilter  FileNameExtensionFilter extends javax swing filechooser FileFilter  I solved my problem by implementing an instance of java io FileFilter  Edit  I did use something similar to  cFreiner s answer  I was trying to use a Java API method instead of writing my own implementation which is why I was trying to use FileNameExtensionFilter  I have many FileChoosers in my application and have used FileNameExtensionFilters for that and I mistakenly assumed that it was also extending java io FileFilter

User · Answer

One-liner in java 8 syntax    pdfTestDir listFiles  dir  name  - gt  name toLowerCase   endsWith   txt

User · Answer

Is there a specific reason you want to use FileNameExtensionFilter   I know this works      private File   getNewTextFiles         return dir listFiles new FilenameFilter              Override         public boolean accept File dir  String name                return name toLowerCase   endsWith   txt

[java] Using File.listFiles with FileNameExtensionFilter

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