The most typical usage is to only show the file types the application can deal with. On "Open" Dialogs, a FileFilter can be used to only shown the files the application can open. On the other side, on "Save as" Dialogs they can be used as a way to let users choose the format in which to save the document.

You will usually add several FileFilters to your FileChooser Widget. The FileChooser will show a ComboBox with the different Filters, that the user can use to choose a specific file type. You should use the setName() method to set the name used as the label for the FileFilter on the ComboBox.

In a FileFilter, you specify the files to shown either as with its MIME type, with the addMimeType() method, or as a shell style glob pattern, with the addPattern() method. You can add several MIME types or patterns to a single FileFilter. This is useful, for example, to provide a "All Supported Files" filter.

As an example, consider the following code:

 FileChooserDialog openDialog;
 FileFilter pngImages, jpegImages, allImages;
 
 openDialog = new FileChooserDialog("Open...", w, FileChooserAction.OPEN);
 
 // you can specify a MIME type...
 pngImages = new FileFilter("Portable Network Graphics (PNG)");
 pngImages.addMimeType("image/png");
 
 // ...or a pattern
 jpegImages = new FileFilter("JPEG Image");
 jpegImages.addPattern("*.jpg");
 
 // of course you can use several patterns or MIME types per filter
 jpegImages.addPattern("*.jpeg");
 
 // and you can use both MIME types and patterns in a single filter
 allImages = new FileFilter("All supported images");
 allImages.addMimeType("image/png");
 allImages.addPattern("*.jpg");
 allImages.addPattern("*.jpeg");
 
 // Finally, you should add each filter to the FileChooser
 openDialog.addFilter(allImages);
 openDialog.addFilter(pngImages);
 openDialog.addFilter(jpegImages);