Here is an example of how to use the Tailer class from the Apache Commons IO library to tail a log file in Java:

import java.io.File;

import org.apache.commons.io.input.Tailer;
import org.apache.commons.io.input.TailerListenerAdapter;

public class LogFileTailer {
    public static void main(String[] args) {
        File logFile = new File("path/to/logfile.log");
        TailerListenerAdapter listener = new TailerListenerAdapter() {
            @Override
            public void handle(String line) {
                System.out.println(line);
            }
        };
        Tailer tailer = new Tailer(logFile, listener, 1000);
        Thread tailerThread = new Thread(tailer);
        tailerThread.setDaemon(true);
        tailerThread.start();
    }
}

In this example, the Tailer class is used to tail the log file located at "path/to/logfile.log". A TailerListenerAdapter is created and overridden to handle new lines that are appended to the log file. The tailer is set to check for new lines every 1000 milliseconds. A new thread is created to run the tailer and is set to be a daemon thread so that it will automatically exit when the main program exits.