code: public String replaceSymbols(String str) {
          Matcher m = SYMBOL_DEF.matcher(str);
          if (m.find()) {
              String symbol = m.group(1);
              String expansion = get(symbol);
              if (expansion != null) {
                  return str.replace(m.group(0), expansion);
              }
          }
  
          return str;
      }
docs: Look for symbols in the given string, if that symbol is present in
  the map of initial properties (or in system properties), replace the
  symbol with the initial property value.
  
  @param str
  String to evaluate for symbols
  @return String with known symbols replaced by the associated values.
  @see #get(String)