Using File.listFiles with FileNameExtensionFilter

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?

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");
	}
});

One-liner in java 8 syntax:

pdfTestDir.listFiles((dir, name) -> name.toLowerCase().endsWith(".txt"));

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");
		}
	});
}

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 -> swingFilter.accept(file);
new File("myDirectory").listFiles(ioFilter);

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 > path.length)
			{
				continue;
			}
			int pStart = path.length - 1;
			int eStart = extension.length - 1;
			boolean success = true;
			for (int i = 0; i <= 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"});

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.