How to check if a String is numeric in Java

Question

How would you check if a String was a number before parsing it

User · Answer

We can try replacing all the numbers from the given string with   quot  quot   ie blank space and if after that the length of the string is zero then we can say that given string contains only numbers  Example  boolean isNumber String str           if str length      0              return false    To check if string is empty                  if str charAt 0      -               str   str replaceFirst  quot - quot   quot  quot      for handling -ve numbers              System out println str                    str   str replaceFirst  quot     quot   quot  quot      to check if it contains more than one decimal points                  if str length      0              return false     to check if it is empty string after removing -ve sign and decimal point         System out println str                    return str replaceAll  quot  0-9  quot   quot  quot   length      0

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As  CraigTP had mentioned in his excellent answer  I also have similar performance concerns on using Exceptions to test whether the string is numerical or not  So I end up splitting the string and use java lang Character isDigit     public static boolean isNumeric String str        for  char c   str toCharArray                  if   Character isDigit c   return false            return true      According to the Javadoc  Character isDigit char  will correctly recognizes non-Latin digits  Performance-wise  I think a simple N number of comparisons where N is the number of characters in the string would be more computationally efficient than doing a regex matching   UPDATE  As pointed by Jean-Fran  ois Corbett in the comment  the above code would only validate positive integers  which covers the majority of my use case  Below is the updated code that correctly validates decimal numbers according to the default locale used in your system  with the assumption that decimal separator only occur once in the string   public static boolean isStringNumeric  String str         DecimalFormatSymbols currentLocaleSymbols   DecimalFormatSymbols getInstance        char localeMinusSign   currentLocaleSymbols getMinusSign         if    Character isDigit  str charAt  0      amp  amp  str charAt  0      localeMinusSign   return false       boolean isDecimalSeparatorFound   false      char localeDecimalSeparator   currentLocaleSymbols getDecimalSeparator         for   char c   str substring  1   toCharArray                   if    Character isDigit  c                           if   c    localeDecimalSeparator  amp  amp   isDecimalSeparatorFound                                 isDecimalSeparatorFound   true                  continue                            return false                      return true

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You could use BigDecimal if the string may contain decimals   try       new java math BigInteger testString     catch NumberFormatException e        throw new RuntimeException  Not a valid number

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If you want to do the check using a regex you should create a final static Pattern object  that way the regex only needs to be compiled once  Compiling the regex takes about as long as performing the match so by taking this precaution you ll cut the execution time of the method in half   final static Pattern NUMBER PATTERN   Pattern compile    -    d       d      static boolean isNumber String input        Matcher m   NUMBER PATTERN matcher input       return m matches        I m assuming a number is a string with nothing but decimal digits in it  possibly a   or - sign at the start and at most one decimal point  not at the end  and no other characters  including commas  spaces  numbers in other counting systems  Roman numerals  hieroglyphs    This solution is succinct and pretty fast but you can shave a couple of milliseconds per million invocations by doing it like this  static boolean isNumber String s        final int len   s length        if  len    0            return false            int dotCount   0      for  int i   0  i  lt  len  i              char c   s charAt i           if  c  lt   0     c  gt   9                 if  i    len - 1     last character must be digit                 return false                else if  c                           if    dotCount  gt  1                        return false                                  else if  i    0    c         amp  amp  c     -        or - allowed at start                 return false                                     return true

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I modified CraigTP s solution to accept scientific notation and both dot and comma as decimal separators as well   -  d        d     eE -  d       example  var re   new RegExp   -  d        d     eE -  d        re test  -6546       true re test  -6546355e-4456       true re test  -6546 355e-4456       true  though debatable re test  -6546 35 5e-4456       false re test  -6546 35 5e-4456 6       false

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Here are two methods that might work   Without using Exceptions   Note   Java is a pass-by-value by default and a String s value is the address of the String s object data  So   when you are doing   stringNumber   stringNumber replaceAll             You have changed the input value to have no spaces  You can remove that line if you want   private boolean isValidStringNumber String stringNumber        if stringNumber isEmpty                  return false             stringNumber   stringNumber replaceAll                char    charNumber   stringNumber toCharArray        for int i  0   i lt charNumber length  i                  if  Character isDigit charNumber i                          return false                      return true      Here is another method in case you want to allow floats This method allegedly allows numbers in the form to pass 1 123 123 123 123 123 123 i have just made it   and i think it needs further testing to ensure it is working   private boolean isValidStringTrueNumber String stringNumber        if stringNumber isEmpty                  return false             stringNumber   stringNumber replaceAll               int countOfDecimalPoint   0      boolean decimalPointPassed   false      boolean commaFound   false      int countOfDigitsBeforeDecimalPoint   0      int countOfDigitsAfterDecimalPoint  0       int commaCounter 0      int countOfDigitsBeforeFirstComma   0       char    charNumber   stringNumber toCharArray        for int i  0   i lt charNumber length  i                  if  commaCounter gt 3    commaCounter lt 0                         return false                    if  Character isDigit charNumber i     Char is not a digit                        if charNumber i                                      if decimalPointPassed                                        return false                                    commaFound   true                    check that next three chars are only digits                  commaCounter   3                            else if charNumber i                                      decimalPointPassed   true                  countOfDecimalPoint                              else                               return false                                  else   Char is a digit                        if   commaCounter gt  0  amp  amp  commaFound                                 if  decimalPointPassed                                        commaCounter--                                               if  commaFound                                countOfDigitsBeforeFirstComma                               if  decimalPointPassed                                countOfDigitsBeforeDecimalPoint                              else                               countOfDigitsAfterDecimalPoint                                      if  commaFound  amp  amp  countOfDigitsBeforeFirstComma gt 3                 return false            if countOfDecimalPoint gt 1                return false             if  decimalPointPassed  amp  amp   countOfDigitsBeforeDecimalPoint  0    countOfDigitsAfterDecimalPoint  0                  return false            return true

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If you using java to develop Android app  you could using TextUtils isDigitsOnly function

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Java 8 Stream  lambda expression  functional interface  All cases handled  string null  string empty etc    String someString   null     something     something  123abc   something  123123   boolean isNumeric   Stream of someString               filter s - gt  s    null  amp  amp   s isEmpty                 filter Pattern compile    D   asPredicate   negate                 mapToLong Long  valueOf               boxed                findAny                isPresent

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This a simple example for this check   public static boolean isNumericString String input        boolean result   false       if input    null  amp  amp  input length    gt  0            char   charArray   input toCharArray             for char c   charArray                if c  gt    0   amp  amp  c  lt    9                        it is a digit                 result   true                else                   result   false                  break                                     return result

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Regex Matching   Here is another example upgraded  CraigTP  regex matching with more validations   public static boolean isNumeric String str        return str matches           - 1     d        1   d              Only one negative sign - allowed and must be in beginning  After negative sign there must be digit  Only one decimal sign   allowed  After decimal sign there must be digit       Regex Test   1                  --                     VALID   1                  --                   INVALID 1                  --                   INVALID 1 1                --                     VALID   1 1 1              --                   INVALID  -1                 --                     VALID   --1                --                   INVALID -1                 --                   INVALID -1 1               --                     VALID   -1 1 1             --                   INVALID

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If you guys using the following method to check   public static boolean isNumeric String str        NumberFormat formatter   NumberFormat getInstance        ParsePosition pos   new ParsePosition 0       formatter parse str  pos       return str length      pos getIndex        Then what happend with the input of very long String  such as I call this method   System out println isNumeric  94328948243242352525243242524243425452342343948923       The result is  true   also it is a too-large-size number  The same thing will happen if you using regex to check  So I d rather using the  parsing  method to check  like this   public static boolean isNumeric String str        try           int number   Integer parseInt str           return true        catch  Exception e            return false            And the result is what I expected

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Do not use Exceptions to validate your values  Use Util libs instead like apache NumberUtils   NumberUtils isNumber myStringValue     Edit   Please notice that  if your string starts with an 0  NumberUtils will interpret your value as hexadecimal   NumberUtils isNumber  07     true NumberUtils isNumber  08     false

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To match only positive base-ten integers  that contains only ASCII digits  use   public static boolean isNumeric String maybeNumeric        return maybeNumeric    null  amp  amp  maybeNumeric matches   0-9

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Based off of other answers I wrote my own and it doesn t use patterns or parsing with exception checking   It checks for a maximum of one minus sign and checks for a maximum of one decimal point   Here are some examples and their results    1    -1    -1 5  and  -1 556  return true   1  5    1A 5    1 5D    -  and  --1  return false  Note  If needed you can modify this to accept a Locale parameter and pass that into the DecimalFormatSymbols getInstance   calls to use a specific Locale instead of the current one    public static boolean isNumeric final String input          Check for null or blank string     if input    null    input isBlank    return false         Retrieve the minus sign and decimal separator characters from the current Locale     final var localeMinusSign   DecimalFormatSymbols getInstance   getMinusSign        final var localeDecimalSeparator   DecimalFormatSymbols getInstance   getDecimalSeparator           Check if first character is a minus sign     final var isNegative   input charAt 0     localeMinusSign        Check if string is not just a minus sign     if  isNegative  amp  amp  input length      1  return false       var isDecimalSeparatorFound   false         If the string has a minus sign ignore the first character     final var startCharIndex   isNegative   1   0         Check if each character is a number or a decimal separator       and make sure string only has a maximum of one decimal separator     for  var i   startCharIndex  i  lt  input length    i              if  Character isDigit input charAt i                  if input charAt i     localeDecimalSeparator  amp  amp   isDecimalSeparatorFound                    isDecimalSeparatorFound   true                else return false                      return true

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Parse it  i e  with Integer parseInt   and simply catch the exception      To clarify  The parseInt function checks if it can parse the number in any case  obviously  and if you want to parse it anyway  you are not going to take any performance hit by actually doing the parsing   If you would not want to parse it  or parse it very  very rarely  you might wish to do it differently of course

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You can use the java util Scanner object   public static boolean isNumeric String inputData          Scanner sc   new Scanner inputData         return sc hasNextInt

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This is the fastest way i know to check if String is Number or not   public static boolean isNumber String str     int i 0  len str length      boolean a false b false c false  d false    if i lt len  amp  amp   str charAt i          str charAt i    -    i      while  i lt len  amp  amp  isDigit str charAt i      i    a true      if i lt len  amp  amp   str charAt i         i      while  i lt len  amp  amp  isDigit str charAt i      i    b true      if i lt len  amp  amp   str charAt i    e     str charAt i    E    amp  amp   a    b    i    c true      if i lt len  amp  amp   str charAt i          str charAt i    -    amp  amp  c  i      while  i lt len  amp  amp  isDigit str charAt i      i    d true     return i  len  amp  amp   a  b   amp  amp    c     c  amp  amp  d      static boolean isDigit char c     return c gt   0   amp  amp  c lt   9

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Why is everyone pushing for exception regex solutions   While I can understand most people are fine with using try catch  if you want to do it frequently    it can be extremely taxing   What I did here was take the regex  the parseNumber   methods  and the array searching method to see which was the most efficient  This time  I only looked at integer numbers   public static boolean isNumericRegex String str        if  str    null          return false      return str matches  -   d        public static boolean isNumericArray String str        if  str    null          return false      char   data   str toCharArray        if  data length  lt   0          return false      int index   0      if  data 0      -   amp  amp  data length  gt  1          index   1      for    index  lt  data length  index              if  data index   lt   0     data index   gt   9      Character isDigit   can go here too              return false            return true     public static boolean isNumericException String str        if  str    null          return false      try                int i      Integer parseInt str         catch  NumberFormatException nfe              return false              return true      The results in speed I got were   Done with  for  int i   0  i  lt  10000000  i        With only valid numbers   59815833  and  -59815833        Array numeric took 395 808192 ms  39 5808192 ns each      Regex took 2609 262595 ms  260 9262595 ns each      Exception numeric took 428 050207 ms  42 8050207 ns each         Negative sign     Array numeric took 355 788273 ms  35 5788273 ns each      Regex took 2746 278466 ms  274 6278466 ns each      Exception numeric took 518 989902 ms  51 8989902 ns each         Single value   1       Array numeric took 317 861267 ms  31 7861267 ns each      Regex took 2505 313201 ms  250 5313201 ns each      Exception numeric took 239 956955 ms  23 9956955 ns each         With Character isDigit       Array numeric took 400 734616 ms  40 0734616 ns each      Regex took 2663 052417 ms  266 3052417 ns each      Exception numeric took 401 235906 ms  40 1235906 ns each   With invalid characters   5981a5833  and  a        Array numeric took 343 205793 ms  34 3205793 ns each      Regex took 2608 739933 ms  260 8739933 ns each      Exception numeric took 7317 201775 ms  731 7201775 ns each         With a single character   a       Array numeric took 291 695519 ms  29 1695519 ns each      Regex took 2287 25378 ms  228 725378 ns each      Exception numeric took 7095 969481 ms  709 5969481 ns each   With null      Array numeric took 214 663834 ms  21 4663834 ns each      Regex took 201 395992 ms  20 1395992 ns each      Exception numeric took 233 049327 ms  23 3049327 ns each      Exception numeric took 6603 669427 ms  660 3669427 ns each  if there is no if null check   Disclaimer  I m not claiming these methods are 100  optimized  they re just for demonstration of the data  Exceptions won if and only if the number is 4 characters or less  and every string is always a number    in which case  why even have a check       In short  it is extremely painful if you run into invalid numbers frequently with the try catch  which makes sense  An important rule I always follow is NEVER use try catch for program flow  This is an example why   Interestingly  the simple if char  lt 0     9 was extremely simple to write  easy to remember  and should work in multiple languages  and wins almost all the test scenarios   The only downside is that I m guessing Integer parseInt   might handle non ASCII numbers  whereas the array searching method does not     For those wondering why I said it s easy to remember the character array one  if you know there s no negative signs  you can easily get away with something condensed as this   public static boolean isNumericArray String str        if  str    null          return false      for  char c   str toCharArray            if  c  lt   0     c  gt   9               return false      return true      Lastly as a final note  I was curious about the assigment operator in the accepted example with all the votes up  Adding in the assignment of  double d   Double parseDouble        is not only useless since you don t even use the value  but it wastes processing time and increased the runtime by a few nanoseconds  which led to a 100-200 ms increase in the tests   I can t see why anyone would do that since it actually is extra work to reduce performance   You d think that would be optimized out    though maybe I should check the bytecode and see what the compiler is doing  That doesn t explain why it always showed up as lengthier for me though if it somehow is optimized out    therefore I wonder what s going on  As a note  By lengthier  I mean running the test for 10000000 iterations  and running that program multiple times  10x   always showed it to be slower   EDIT  Updated a test for Character isDigit

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Try this   public  boolean isNumber String str               short count   0      char chc        0   1   2   3   4   5   6   7   8   9       -            for  char c   str toCharArray                     for  int i   0 i  lt  chc length i                          if  c     chc i                    count                                                                     if  count    str length              return false      else         return true

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This is generally done with a simple user-defined function  i e  Roll-your-own  isNumeric  function    Something like   public static boolean isNumeric String str       try         Double parseDouble str         return true      catch NumberFormatException e         return false              However  if you re calling this function a lot  and you expect many of the checks to fail due to not being a number then performance of this mechanism will not be great  since you re relying upon exceptions being thrown for each failure  which is a fairly expensive operation   An alternative approach may be to use a regular expression to check for validity of being a number   public static boolean isNumeric String str      return str matches  -   d       d          match a number with optional  -  and decimal      Be careful with the above RegEx mechanism  though  as it will fail if you re using non-Arabic digits  i e  numerals other than 0 through to 9    This is because the   d  part of the RegEx will only match  0-9  and effectively isn t internationally numerically aware    Thanks to OregonGhost for pointing this out    Or even another alternative is to use Java s built-in java text NumberFormat object to see if  after parsing the string the parser position is at the end of the string   If it is  we can assume the entire string is numeric   public static boolean isNumeric String str      NumberFormat formatter   NumberFormat getInstance      ParsePosition pos   new ParsePosition 0     formatter parse str  pos     return str length      pos getIndex

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import java util Scanner   public class TestDemo       public static void main String   args            boolean flag   true          Scanner sc   new Scanner System in           System out println  Enter the String             String str   sc nextLine             for  int i   0  i  lt  str length    i                  if str charAt i   gt  48  amp  amp  str charAt i   lt  58                    flag   false                  break                                   if flag    true                System out println  String is a valid String               else               System out println  String contains number

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That s why I like the Try  approach in  NET  In addition to the traditional Parse method that s like the Java one  you also have a TryParse method  I m not good in Java syntax  out parameters    so please treat the following as some kind of pseudo-code  It should make the concept clear though   boolean parseInteger String s  out int number        try           number   Integer parseInt myString           return true        catch NumberFormatException e            return false            Usage   int num  if  parseInteger  23   out num            Do something with num

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Here was my answer to the problem   A catch all convenience method which you can use to parse any String with any type of parser  isParsable Object parser  String str   The parser can be a Class or an object  This will also allows you to use custom parsers you ve written and should work for ever scenario  eg   isParsable Integer class   11    isParsable Double class   11 11    Object dateFormater   new java text SimpleDateFormat  yyyy MM dd G  at  HH mm ss z    isParsable dateFormater   2001 07 04 AD at 12 08 56 PDT      Here s my code complete with method descriptions   import java lang reflect            METHOD  isParsable lt p gt  lt p gt         This method will look through the methods of the specified  lt code gt from lt  code gt  parameter    looking for a public method name starting with  parse  which has only one String    parameter  lt p gt         The  lt code gt parser lt  code gt  parameter can be a class or an instantiated object  eg      lt code gt Integer class lt  code gt  or  lt code gt new Integer 1  lt  code gt   If you use a     lt code gt Class lt  code gt  type then only static methods are considered  lt p gt         When looping through potential methods  it first looks at the  lt code gt Class lt  code gt  associated    with the  lt code gt parser lt  code gt  parameter  then looks through the methods of the parent s class    followed by subsequent ancestors  using the first method that matches the criteria specified    above  lt p gt         This method will hide any normal parse exceptions  but throws any exceptions due to    programmatic errors  eg  NullPointerExceptions  etc  If you specify a  lt code gt parser lt  code gt     parameter which has no matching parse methods  a NoSuchMethodException will be thrown    embedded within a RuntimeException  lt p gt  lt p gt         Example  lt br gt      lt code gt isParsable Boolean class   true    lt br gt     isParsable Integer class   11    lt br gt     isParsable Double class   11 11    lt br gt     Object dateFormater   new java text SimpleDateFormat  yyyy MM dd G  at  HH mm ss z    lt br gt     isParsable dateFormater   2001 07 04 AD at 12 08 56 PDT    lt br gt  lt  code gt      lt p gt          param parser    The Class type or instantiated Object to find a parse method in      param str   The String you want to parse         return true if a parse method was found and completed without exception     throws java lang NoSuchMethodException If no such method is accessible      public static boolean isParsable Object parser  String str        Class theClass    parser instanceof Class   Class parser  parser getClass         boolean staticOnly    parser    theClass   foundAtLeastOne   false      Method   methods   theClass getMethods            Loop over methods     for  int index   0  index  lt  methods length  index              Method method   methods index               If method starts with parse  is public and has one String parameter             If the parser parameter was a Class  then also ensure the method is static           if method getName   startsWith  parse    amp  amp                staticOnly    Modifier isStatic method getModifiers      amp  amp              Modifier isPublic method getModifiers     amp  amp              method getGenericParameterTypes   length    1  amp  amp              method getGenericParameterTypes   0     String class                        try                   foundAtLeastOne   true                  method invoke parser  str                   return true     Successfully parsed without exception               catch  Exception exception                       If invoke problem  try a different method                   if   exception instanceof IllegalArgumentException   amp  amp                       exception instanceof IllegalAccessException   amp  amp                       exception instanceof InvocationTargetException                           continue     Look for other parse methods                       Parse method refuses to parse  look for another different method                 continue     Look for other parse methods                                       No more accessible parse method could be found      if foundAtLeastOne  return false      else throw new RuntimeException new NoSuchMethodException                METHOD  willParse lt p gt  lt p gt         A convienence method which calls the isParseable method  but does not throw any exceptions    which could be thrown through programatic errors  lt p gt         Use of   link  isParseable Object  String  isParseable  is recommended for use so programatic    errors can be caught in development  unless the value of the  lt code gt parser lt  code gt  parameter is    unpredictable  or normal programtic exceptions should be ignored  lt p gt         See   link  isParseable Object  String  isParseable  for full description of method    usability  lt p gt          param parser    The Class type or instantiated Object to find a parse method in      param str   The String you want to parse         return true if a parse method was found and completed without exception     see  isParseable Object  String  for full description of method usability      public static boolean willParse Object parser  String str        try           return isParsable parser  str         catch Throwable exception            return false

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public static boolean isNumeric String str        return str matches  -   d     d           CraigTP s regular expression  shown above  produces some false positives   E g   23y4  will be counted as a number because     matches any character not the decimal point   Also it will reject any number with a leading      An alternative which avoids these two minor problems is   public static boolean isNumeric String str        return str matches    -    d       d

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only int public static boolean isNumber int num         return  num  gt   48  amp  amp  c  lt   57      0 - 9       is type of number including   - e E  public static boolean isNumber String s         boolean isNumber   true      for int i   0  i  lt  s length    amp  amp  isNumber  i                   char c   s charAt i           isNumber   isNumber  amp                 c  gt    0   amp  amp  c  lt    9       c             c     e       c     E       c                             return isInteger        is type of number  public static boolean isInteger String s         boolean isInteger   true      for int i   0  i  lt  s length    amp  amp  isInteger  i                   char c   s charAt i           isInteger   isInteger  amp    c  gt    0   amp  amp  c  lt    9               return isInteger     public static boolean isNumeric String s         try               Double parseDouble s           return true            catch  Exception e                 return false

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Parallel checking for very long strings using IntStream  In Java 8  the following tests if all characters of the given string are within  0  to  9   Mind that the empty string is accepted   string chars   unordered   parallel   allMatch  i - gt   0   lt   i  amp  amp   9   gt   i

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I think the only way to reliably tell if a string is a number  is to parse it  So I would just parse it  and if it s a number  you get the number in an int for free

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You can use NumberFormat parse   try        NumberFormat getInstance   parse value     catch ParseException e           Not a number

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Exceptions are expensive  but in this case the RegEx takes much longer  The code below shows a simple test of two functions -- one using exceptions and one using regex  On my machine the RegEx version is 10 times slower than the exception   import java util Date    public class IsNumeric    public static boolean isNumericOne String s        return s matches  -   d       d          match a number with optional  -  and decimal           public static boolean isNumericTwo String s        try           Double parseDouble s           return true        catch  Exception e            return false           public static void main String    args         String test    12345 F        long before   new Date   getTime             for int x 0 x lt 1000000   x              isNumericTwo test           isNumericOne test             long after   new Date   getTime         System out println after-before

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String text  hello 123   if Pattern matches  0-9      true System out println  String  text

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please check below code  public static boolean isDigitsOnly CharSequence str        final int len   str length        for  int i   0  i  lt  len  i              if   Character isDigit str charAt i                  return false                      return true

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if you are on android  then you should use   android text TextUtils isDigitsOnly CharSequence str    documentation can be found here  keep it simple  mostly everybody can  re-program   the same thing

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Google s Guava library provides a nice helper method to do this  Ints tryParse  You use it like Integer parseInt but it returns null rather than throw an Exception if the string does not parse to a valid integer  Note that it returns Integer  not int  so you have to convert autobox it back to int   Example   String s1    22   String s2    22 2   Integer oInt1   Ints tryParse s1   Integer oInt2   Ints tryParse s2    int i1   -1  if  oInt1    null        i1   oInt1 intValue      int i2   -1  if  oInt2    null        i2   oInt2 intValue       System out println i1       prints 22 System out println i2       prints -1   However  as of the current release -- Guava r11 -- it is still marked  Beta    I haven t benchmarked it  Looking at the source code there is some overhead from a lot of sanity checking but in the end they use Character digit string charAt idx    similar  but slightly different from  the answer from  Ibrahim above  There is no exception handling overhead under the covers in their implementation

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You can use NumberUtils isCreatable   from Apache Commons Lang   Since NumberUtils isNumber will be deprecated in 4 0  so use  NumberUtils isCreatable   instead

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I have illustrated some conditions to check numbers and decimals without using any API   Check Fix Length 1 digit number  Character isDigit char    Check Fix Length number  Assume length is 6   String number    132452   if number matches    0-9  6      System out println  6 digits number identified      Check Varying Length number between  Assume 4 to 6 length        n m   n  lt   length  lt   m String number    132452   if number matches    0-9  4 6      System out println  Number Identified between 4 to 6 length     String number    132   if  number matches    0-9  4 6      System out println  Number not in length range or different format      Check Varying Length decimal number between  Assume 4 to 7 length       It will not count the      Period  in length String decimal    132 45   if decimal matches   -  0-9        0-9    4 6     System out println  Numbers Identified between 4 to 7     String decimal    1 12   if decimal matches   -  0-9        0-9    4 6     System out println  Numbers Identified between 4 to 7     String decimal    1234   if decimal matches   -  0-9        0-9    4 6     System out println  Numbers Identified between 4 to 7     String decimal    -10 123   if decimal matches   -  0-9        0-9    4 6     System out println  Numbers Identified between 4 to 7     String decimal    123  4   if  decimal matches   -  0-9        0-9    4 6     System out println  Decimal not in range or different format     String decimal    132   if  decimal matches   -  0-9        0-9    4 6     System out println  Decimal not in range or different format     String decimal    1 1   if  decimal matches   -  0-9        0-9    4 6     System out println  Decimal not in range or different format      Hope it will help manyone

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With Apache Commons Lang 3 5 and above  NumberUtils isCreatable or StringUtils isNumeric   With Apache Commons Lang 3 4 and below  NumberUtils isNumber or StringUtils isNumeric   You can also use StringUtils isNumericSpace which returns true for empty strings  and ignores internal spaces in the string  Another way is to use NumberUtils isParsable which basically checks the number is parsable according to Java   The linked javadocs contain detailed examples for each method

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Java 8 lambda expressions   String someString    123123   boolean isNumeric   someString chars   allMatch  Character  isDigit

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A well-performing approach avoiding try-catch and handling negative numbers and scientific notation   Pattern PATTERN   Pattern compile     - 0 -  1-9   d        d    E  d          public static boolean isNumeric  String value          return value    null  amp  amp  PATTERN matcher  value   matches

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Here is my class for checking if a string is numeric  It also fixes numerical strings   Features    Removes unnecessary zeros   12 0000000  -   12    Removes unnecessary zeros   12 0580000  -   12 058    Removes non numerical characters   12 00sdfsdf00  -   12    Handles negative string values   -12 020000  -   -12 02   Removes multiple dots   -12 0 20 000  -   -12 02   No extra libraries  just standard Java   Here you go     public class NumUtils                  Transforms a string to an integer  If no numerical chars returns a String  0                  param str         return retStr             static String makeToInteger String str            String s   str          double d          d   Double parseDouble makeToDouble s            int i    int   d   0 5D           String retStr   String valueOf i           System out printf retStr                   return retStr                        Transforms a string to an double  If no numerical chars returns a String  0                  param str         return retStr             static String makeToDouble String str             Boolean dotWasFound   false          String orgStr   str          String retStr          int firstDotPos   0          Boolean negative   false             check if str is null         if str length    0               str  0                        check if first sign is  -          if  str charAt 0      -                 negative   true                       check if str containg any number or else set the string to  0          if   str matches      d                     str    0                        Replace     with       for some european users who use the     as decimal separator          str   str replaceAll                    str   str replaceAll      d                     Removes the any second dots         for  int i char   0  i char  lt  str length    i char                  if  str charAt i char                            dotWasFound   true                  firstDotPos   i char                  break                                  if  dotWasFound                String befDot   str substring 0  firstDotPos   1               String aftDot   str substring firstDotPos   1  str length                 aftDot   aftDot replaceAll                         str   befDot   aftDot                       Removes zeros from the begining         double uglyMethod   Double parseDouble str           str   String valueOf uglyMethod              Removes the  0         str   str replaceAll    0-9     0    0-9         1 2             retStr   str           if  negative                retStr    -  retStr                     return retStr              static boolean isNumeric String str            try               double d   Double parseDouble str             catch  NumberFormatException nfe                return false                    return true

[java] How to check if a String is numeric in Java

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