ParseInt method of Java

public static int parseInt(String s, int radix)
                    throws NumberFormatException {
                if (s == null) {
                    throw new NumberFormatException("null");
                }

                if (radix < Character.MIN_RADIX) {
                    throw new NumberFormatException("radix " + radix
                            + " less than Character.MIN_RADIX");
                }

                if (radix > Character.MAX_RADIX) {
                    throw new NumberFormatException("radix " + radix
                            + " greater than Character.MAX_RADIX");
                }

                int result = 0;
                boolean negative = false;
                int i = 0, len = s.length();
                int limit = -Integer.MAX_VALUE;
                int multmin;
                int digit;

                if (len > 0) {
                    char firstChar = s.charAt(0);
                    if (firstChar < '0') { // Possible leading "+" or "-"
                        if (firstChar == '-') {
                            negative = true;
                            limit = Integer.MIN_VALUE;
                        } else if (firstChar != '+')
                            throw NumberFormatException.forInputString(s);

                        if (len == 1) // Cannot have lone "+" or "-"
                            throw NumberFormatException.forInputString(s);
                        i++;
                    }
                    multmin = limit / radix;
                    while (i < len) {
                        // Accumulating negatively avoids surprises near MAX_VALUE
                        digit = Character.digit(s.charAt(i++), radix);
                        if (digit < 0) {
                            throw NumberFormatException.forInputString(s);
                        }
                        if (result < multmin) {
                            throw NumberFormatException.forInputString(s);
                        }
                        result *= radix;
                        if (result < limit + digit) {
                            throw NumberFormatException.forInputString(s);
                        }
                        result -= digit;
                    }
                } else {
                    throw NumberFormatException.forInputString(s);
                }
                return negative ? result : -result;
            }