A Logger maybe for re-use

Logger.java

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.swing.JOptionPane;

public final class Logger {
	
	private static Logger INSTANCE;
	private static String logfile;
	private static SimpleDateFormat sdf = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss");
	
	private boolean debug;
	private boolean date;
	
	private Logger() {
		logfile = "error.log";
	}
	
	public static Logger getInstance() {
		if (INSTANCE == null) INSTANCE = new Logger();
		return INSTANCE;
	}
	
	public void log(String s) {
		System.out.println(formatDate(s));
	}
	
	public void debug(String s) {
		if (debug) log(s);
	}
	
	public void err(String s) {
		System.err.println(formatDate(s));
	}
 	
	public void box(String s) {
		JOptionPane.showMessageDialog(null, formatDate(s));
	}
	
	public void fprint(String s) {
		FileWriter writer = null;
		try {
			writer = new FileWriter(new File(logfile), true);
			writer.write(formatDate(s));
			writer.write('\n');
			writer.flush();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				if (writer != null)
					writer.close();
			} catch (IOException e2) {
				e2.printStackTrace();
			}
		}
	}
	
	private String formatDate(String s) {
		return date ? new StringBuilder().append('[').append(currentDate()).append(']').append(' ').append(s).toString() : s;
	}
	
	private static String currentDate() {
		return sdf.format(new Date());
	}
	
	public boolean debug() {
		debug = !debug;
		return debug;
	}
	public boolean date() {
		date = !date;
		return date;
	}
}