Here is an example of how to use the AbstractFileFilter class from the org.apache.commons.io package in Java:

import java.io.File;
import org.apache.commons.io.filefilter.AbstractFileFilter;

public class MyFileFilter extends AbstractFileFilter {

    public boolean accept(File file) {
        // custom logic to determine if the file should be accepted
        if (file.getName().endsWith(".txt")) {
            return true;
        }
        return false;
    }
}

// Usage
MyFileFilter fileFilter = new MyFileFilter();
File[] files = new File("/path/to/directory").listFiles(fileFilter);

This example will filter all files that end with .txt from a directory. you can use this filter in other classes such as FileUtils.listFiles() to filter files.