A NumberFormat object converts integers and floating 
point numbers using one of NumberFormat's five overloaded 
format() methods:
public final String format(long number)
public final String format(double number)
public abstract StringBuffer format(long number, StringBuffer toAppendTo, 
 FieldPosition pos)
public abstract StringBuffer format(double number, StringBuffer toAppendTo, 
 FieldPosition pos)
public final StringBuffer format(Object number, StringBuffer toAppendTo, 
 FieldPosition pos)