class FileLoggerModule {

  private static FileLoggerModule singleton = null;

  private static final String OUTPUT_FILE = "output.txt";
  private static final String ERROR_FILE = "error.txt";

  public PrintStream output = null;
  public PrintStream error = null;

  private FileLoggerModule() {
  }

  /**
   * Static method to get single instance of class.
   *
   * @return singleton instance of FileLoggerModule
   */
  public static FileLoggerModule getSingleton() {<FILL_FUNCTION_BODY>}

  /**
   * Following method performs the initialization.
   *
   * @throws FileNotFoundException if program is not able to find log files (output.txt and
   *                               error.txt)
   */
  public FileLoggerModule prepare() throws FileNotFoundException {

    LOGGER.debug("FileLoggerModule::prepare();");

    this.output = new PrintStream(new FileOutputStream(OUTPUT_FILE));
    this.error = new PrintStream(new FileOutputStream(ERROR_FILE));

    return this;
  }

  /**
   * Following method performs the finalization.
   */
  public void unprepare() {

    if (this.output != null) {

      this.output.flush();
      this.output.close();
    }

    if (this.error != null) {

      this.error.flush();
      this.error.close();
    }

    LOGGER.debug("FileLoggerModule::unprepare();");
  }

  /**
   * Used to print a message.
   *
   * @param value will be printed in file
   */
  public void printString(final String value) {
    this.output.println(value);
  }

  /**
   * Used to print a error message.
   *
   * @param value will be printed on error file
   */
  public void printErrorString(final String value) {
    this.error.println(value);
  }
}


    if (FileLoggerModule.singleton == null) {
      FileLoggerModule.singleton = new FileLoggerModule();
    }

    return FileLoggerModule.singleton;
  
<no_super_class>