How to check that a string is parseable to a double

Question

Is there a native way  preferably without implementing your own method  to check that a string is parseable with Double parseDouble

User · Answer

Google s Guava library provides a nice helper method to do this  Doubles tryParse String   You use it like Double parseDouble but it returns null rather than throwing an exception if the string does not parse to a double

User · Answer

Something like below should suffice  -  String decimalPattern      0-9        0-9        String number  20 00     boolean match   Pattern matches decimalPattern  number   System out println match     if true then decimal else not

User · Answer

The common approach would be to check it with a regular expression like it s also suggested inside the Double valueOf String  documentation   The regexp provided there  or included below  should cover all valid floating point cases  so you don t need to fiddle with it  since you will eventually miss out on some of the finer points   If you don t want to do that  try catch is still an option   The regexp suggested by the JavaDoc is included below   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        Double valueOf myString      Will not throw NumberFormatException   else          Perform suitable alternative action

User · Answer

You can always wrap Double parseDouble   in a try catch block   try     Double parseDouble number     catch NumberFormatException e        not a double

User · Answer

Apache  as usual  has a good answer from Apache Commons-Lang in the form of  NumberUtils isCreatable String    Handles nulls  no try catch block required

User · Answer

All answers are OK  depending on how academic you want to be  If you wish to follow the Java specifications accurately  use the following   private static final Pattern DOUBLE PATTERN   Pattern compile          x00-  x20    -   NaN Infinity       p Digit             p Digit                eE   -     p Digit               p Digit      eE   -     p Digit                   0 xX    p XDigit            0 xX    p XDigit            p XDigit               pP   -     p Digit      fFdD       x00-  x20       public static boolean isFloat String s        return DOUBLE PATTERN matcher s  matches        This code is based on the JavaDocs at Double

[java] How to check that a string is parseable to a double?

Examples related to java

Examples related to string

Examples related to parsing

Examples related to floating-point