The ' symbol is used to quote literal symbols : DecimalFormat « I18N « Java Tutorial

1. Java Tutorial
2. I18N
3. DecimalFormat

import java.text.DecimalFormat;
import java.text.NumberFormat;

public class Main {
  public static void main(String[] argv) throws Exception {

    NumberFormat formatter = new DecimalFormat("'#'#");

    String s = formatter.format(-1234.567); 

    System.out.println(s);
  }
}
//-#1235

13.13.DecimalFormat
	13.13.1.	new DecimalFormat('0.00')
	13.13.2.	new DecimalFormat('#.#') two digits
	13.13.3.	new DecimalFormat('#.######') more digits
	13.13.4.	new DecimalFormat('.######'), keep fraction
	13.13.5.	new DecimalFormat('#.000000'), append zero
	13.13.6.	new DecimalFormat('#,###,###'), group
	13.13.7.	Arabic Digits
	13.13.8.	Format a number with leading zeros
	13.13.9.	The . symbol indicates the decimal point
	13.13.10.	The , symbol is used to group numbers
	13.13.11.	The ; symbol is used to specify an alternate pattern for negative values
	13.13.12.	The ' symbol is used to quote literal symbols
	13.13.13.	Use group separators and show trailing zeros
	13.13.14.	Display numbers in scientific notation
	13.13.15.	Displaying numbers with commas
	13.13.16.	new DecimalFormat('##00')
	13.13.17.	The 0 symbol shows a digit or 0 if no digit present