Java Regex Double Validate parseDouble(String myString)

Description

Check if a string can be parsed correctly.

License

Open Source License

Parameter

Parameter	Description
myString	String to parse and retrieve a Double

Return

Double value, or null if the string is invalid.

Declaration

public static Double parseDouble(String myString) 

Method Source Code

//package com.java2s;
//License from project: Open Source License 

import java.util.regex.Pattern;

public class Main {
    /**//from   w w  w  .  j  av a 2  s.c  o m
     * Check if a string can be parsed correctly. This is taken
     * straight from the Java API.
     * @param myString String to parse and retrieve a Double
     * @return Double value, or null if the string is invalid.
     */
    public static Double parseDouble(String myString) {
        final String Digits = "(\\p{Digit}+)";
        final String HexDigits = "(\\p{XDigit}+)";
        // an exponent is 'e' or 'E' followed by an optionally 
        // signed decimal integer.
        final String Exp = "[eE][+-]?" + Digits;
        final String fpRegex = ("[\\x00-\\x20]*" + // Optional leading "whitespace"
                "[+-]?(" + // Optional sign character
                "NaN|" + // "NaN" string
                "Infinity|" + // "Infinity" string

                // A decimal floating-point string representing a finite positive
                // number without a leading sign has at most five basic pieces:
                // Digits . Digits ExponentPart FloatTypeSuffix
                // 
                // Since this method allows integer-only strings as input
                // in addition to strings of floating-point literals, the
                // two sub-patterns below are simplifications of the grammar
                // productions from the Java Language Specification, 2nd 
                // edition, section 3.10.2.

                // Digits ._opt Digits_opt ExponentPart_opt FloatTypeSuffix_opt
                "(((" + Digits + "(\\.)?(" + Digits + "?)(" + Exp + ")?)|" +

                // . Digits ExponentPart_opt FloatTypeSuffix_opt
                "(\\.(" + Digits + ")(" + Exp + ")?)|" +

                // Hexadecimal strings
                "((" +
                // 0[xX] HexDigits ._opt BinaryExponent FloatTypeSuffix_opt
                "(0[xX]" + HexDigits + "(\\.)?)|" +

                // 0[xX] HexDigits_opt . HexDigits BinaryExponent FloatTypeSuffix_opt
                "(0[xX]" + HexDigits + "?(\\.)" + HexDigits + ")" +

                ")[pP][+-]?" + Digits + "))" + "[fFdD]?))" + "[\\x00-\\x20]*");// Optional trailing "whitespace"

        if (Pattern.matches(fpRegex, myString))
            return Double.valueOf(myString); // Will not throw NumberFormatException
        else {
            return null;
        }

    }
}

Related

1. parseDouble(final String text)
2. parseDouble(Object object)
3. parseDouble(Object value, Double replace)
4. parseDouble(String s)
5. parseDouble(String str)
6. parseDoubleList(String list)