A Java Mac OS X "show file dialog" method

The following code is a “show file dialog” method that works on Mac OS X. I wrote the code a long time ago, but this still looks like the preferred way to show a file-chooser dialog on OS X, as of Java 7 and Mac OS X 10.9 and 10.10.

Here’s the Java source code:

/**
 * @param frame - parent frame
 * @param dialogTitle - dialog title
 * @param defaultDirectory - default directory
 * @param fileType - something like "*.jpg"
 * @return Returns null if the user selected nothing, otherwise returns the canonical filename (directory + fileSep + filename).
 */
String showFileDialog (Frame frame, String dialogTitle, String defaultDirectory, String fileType)
{
    FileDialog fd = new FileDialog(frame, dialogTitle, FileDialog.LOAD);
    fd.setFile(fileType);
    fd.setDirectory(defaultDirectory);
    fd.setLocationRelativeTo(frame);
    fd.setVisible(true);
    String directory = fd.getDirectory();
    String filename = fd.getFile();
    if (directory == null || filename == null || directory.trim().equals("") || filename.trim().equals(""))
    {
        return null;
    }
    else
    {
        // this was not needed on mac os x:
        //return directory + System.getProperty("file.separator") + filename;
        return directory + filename;
    }
}