Hi,

I'm not sure what it is called but in Java you can define a class inside
another class.

I have a GUI (extends javax.swing.JFrame) which, among other things,
allows some file selections based on a file extension, to achieve this it
uses the File class method listFiles() taking a FilenameFilter.

FilenameFilter is an interface with a single method to define called
accept(File dir, String name). Rather than creating a new file containing
a class of one method which implements FilenameFilter I've put that class
inside my GUI class like this:

public class FileRename extends javax.swing.JFrame
{
    public FileRename()
    {
        initComponents();
    }

...lots of methods...followed by the class within the class here:

private class FNFilter implements FilenameFilter
{
    private String fileExtension;
    public FNFilter(String extension)
    {
        fileExtension = extension;
    }

    public boolean accept(File dir, String name)
    {
        File checkDir = new File(dir, name);
        if (checkDir.isDirectory() == true)
        {
            return false;
        }

        name = name.toLowerCase();
        fileExtension = fileExtension.toLowerCase();

        if (name.endsWith(fileExtension) == true)
        {
            return true;
        }
        return false;
    }
}  // End of FNFilter class

}  // End of FileRename class

Is this kind of coding generally acceptable or is it considered messy or a
bit of a hack? If so, how should it be done?

Thanks,

MS