Java String - See if a string contains only numbers and not letters

Question

I have a string that I load throughout my application  and it changes from numbers to letters and such  I have a simple if statement to see if it contains letters or numbers but  something isn t quite working correctly  Here is a snippet   String text    abc    String number    if  text contains   a-zA-Z        false  amp  amp  text length    gt  2        number   text       Although the text variable does contain letters  the condition returns as true  The and  amp  amp  should eval as both conditions having to be true in order to process the number   text                                    Solution    I was able to solve this by using this following code provided by a comment on this question  All other post are valid as well   What I used that worked came from the first comment  Although all the example codes provided seems to be valid as well   String text    abc    String number    if  Pattern matches   a-zA-Z     text     false  amp  amp  text length    gt  2        number   text

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Here is a sample  Find only the digits in a String and Process formation as needed  text replaceAll  quot   d      quot    quot  0  quot     For more info check google Docs https   developer android com reference java util regex Pattern Where you can use Pattern

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Here is my code  hope this will help you     public boolean isDigitOnly String text        boolean isDigit   false       if  text matches   0-9      amp  amp  text length    gt  2            isDigit   true       else           isDigit   false             return isDigit

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If you ll be processing the number as text  then change   if  text contains   a-zA-Z        false  amp  amp  text length    gt  2     to   if  text matches   0-9      amp  amp  text length    gt  2      Instead of checking that the string doesn t contain alphabetic characters  check to be sure it contains only numerics   If you actually want to use the numeric value  use Integer parseInt   or Double parseDouble   as others have explained below     As a side note  it s generally considered bad practice to compare boolean values to true or false   Just use if  condition  or if   condition

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You can also use NumberUtil isCreatable String str  from Apache Commons

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boolean isNum   text chars   allMatch c -  c    48  amp  amp  c  lt   57

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There are lots of facilities to obtain numbers from Strings in Java  and vice versa   You may want to skip the regex part to spare yourself the complication of that    For example  you could try and see what Double parseDouble String s  returns for you  It should throw a NumberFormatException if it does not find an appropriate value in the string  I would suggest this technique because you could actually make use of the value represented by the String as a numeric type

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public class Test    public static void main String   args        Scanner sc   new Scanner System in       String str      boolean status false      System out println  quot Enter the String    quot        str   sc nextLine             char ch     str toCharArray             for int i 0 i lt ch length i              if ch i    1   ch i    2   ch i    3   ch i    4   ch i    5   ch i    6   ch i    7   ch i    8   ch i    9   ch i    0                 ch i    0                           for int i 0 i lt ch length i              if ch i     0                System out println  quot Mixture of letters and Digits quot                status   false              break                    else             status   true                 if status    true           System out println  quot Only Digits are present quot

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Performance-wise parseInt and such are much worser than other solutions  because at least require exception handling   I ve run jmh tests and have found that iterating over String using charAt and comparing chars with boundary chars is the fastest way to test if string contains only digits   JMH testing  Tests compare performance of Character isDigit vs Pattern matcher   matches vs Long parseLong vs checking char values   These ways can produce different result for non-ascii strings and strings containing   - signs   Tests run in Throughput mode  greater is better  with 5 warmup iterations and 5 test iterations   Results  Note that parseLong is almost 100 times slower than isDigit for first test load      Test load with 25  valid strings  75  strings contain non-digit symbols   Benchmark       Mode  Cnt  Score   Error  Units testIsDigit    thrpt    5  9 275    2 348  ops s testPattern    thrpt    5  2 135    0 697  ops s testParseLong  thrpt    5  0 166    0 021  ops s     Test load with 50  valid strings  50  strings contain non-digit symbols   Benchmark              Mode  Cnt  Score   Error  Units testCharBetween       thrpt    5  16 773    0 401  ops s testCharAtIsDigit     thrpt    5  8 917    0 767  ops s testCharArrayIsDigit  thrpt    5  6 553    0 425  ops s testPattern           thrpt    5  1 287    0 057  ops s testIntStreamCodes    thrpt    5  0 966    0 051  ops s testParseLong         thrpt    5  0 174    0 013  ops s testParseInt          thrpt    5  0 078    0 001  ops s   Test suite   State Scope Benchmark  public class StringIsNumberBenchmark       private static final long CYCLES   1 000 000L      private static final String   STRINGS     12345678901   98765432177   58745896328   35741596328    123456789a1    1a345678901    1234567890         private static final Pattern PATTERN   Pattern compile    d           Benchmark     public void testPattern             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  b   PATTERN matcher s  matches                                        Benchmark     public void testParseLong             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  try                       Long parseLong s                       b   true                    catch  NumberFormatException e                           no-op                                                       Benchmark     public void testCharArrayIsDigit             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  for  char c   s toCharArray                          b   Character isDigit c                       if   b                            break                                                                              Benchmark     public void testCharAtIsDigit             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  for  int j   0  j  lt  s length    j                          b   Character isDigit s charAt j                        if   b                            break                                                                              Benchmark     public void testIntStreamCodes             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  b   s chars   allMatch c - gt  c  gt  47  amp  amp  c  lt  58                                       Benchmark     public void testCharBetween             for  int i   0  i  lt  CYCLES  i                  for  String s   STRINGS                    boolean b   false                  for  int j   0  j  lt  s length    j                          char charr   s charAt j                       b    0   lt   charr  amp  amp  charr  lt    9                       if   b                            break                                                                            Updated on Feb 23  2018   Add two more cases - one using charAt instead of creating extra array and another using IntStream of char codes Add immediate break if non-digit found for looped test cases Return false for empty string for looped test cases   Updated on Feb 23  2018   Add one more test case  the fastest   that compares char value without using stream

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Slightly modified version of Adam Bodrogi s   public class NumericStr     public static void main String   args        System out println  Matches    NumericStr isNumeric  20                Should be true     System out println  Matches    NumericStr isNumeric  20 00                 Should be true     System out println  Matches    NumericStr isNumeric  30 01                 Should be true     System out println  Matches    NumericStr isNumeric  30 000 01                 Should be true     System out println  Matches    NumericStr isNumeric  -2980                 Should be true     System out println  Matches    NumericStr isNumeric   20                   Should be true     System out println  Matches    NumericStr isNumeric  jdl                   Should be false     System out println  Matches    NumericStr isNumeric  2lk0                  Should be false    public static boolean isNumeric String stringVal        if  stringVal matches          -      d               d                return true             return false        Had to use this today so just posted my modifications  Includes currency  thousands comma or period notation  and some validations  Does not include other currency notations  euro  cent   verification commas are every third digit

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import java util     class Class1       public static void main String   argh            boolean ans   CheckNumbers  123            if  ans    true                System out println  String contains numbers only              else               System out println  String contains other values as well                           public static boolean CheckNumbers String input            for  int ctr   0  ctr  lt  input length    ctr                  if   1234567890  contains Character valueOf input charAt ctr   toString                       continue                else                   return false                                  return true

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In order to simply check the string that it contains only ALPHABETS use the following code    if  text matches   a-zA-Z            your operations     In order to simply check the string that it contains only NUMBER use the following code    if  text matches   0-9            your operations     Hope this will help to someone

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This is how I would do it   if text matches    0-9       amp  amp  text length    gt  2                 The   will avoid a partial match e g  1B

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Working test example      import java util regex Matcher  import java util regex Pattern   import org apache commons lang3 StringUtils   public class PaserNo        public static void main String args               String text    gg            if   StringUtils isBlank text                 if  stringContainsNumber text                     int no Integer parseInt text trim                     System out println  inside  no                  else                   System out println  Outside                                    System out println  Done               public static boolean stringContainsNumber String s            Pattern p   Pattern compile   0-9             Matcher m   p matcher s           return m find              Still your code can be break by  1a  etc so you need to check exception   if   StringUtils isBlank studentNbr                     try                      if  isStringContainsNumber studentNbr                         account setStudentNbr Integer parseInt studentNbr trim                                         catch Exception e                       e printStackTrace                        logger info  Exception during parse studentNbr  e getMessage                                       Method for checking no is string or not  private boolean isStringContainsNumber String s            Pattern p   Pattern compile   0-9             Matcher m   p matcher s           return m find

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You can use Regex Match  if text matches    d    amp  amp  text length    gt  2       System out println  number        Or you could use onversions like Integer parseInt String  or better Long parseLong String  for bigger numbers like for example   private boolean onlyContainsNumbers String text        try           Long parseLong text           return true        catch  NumberFormatException ex            return false             And then test with   if  onlyContainsNumbers text   amp  amp  text length    gt  2           do Stuff

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Character first letter or number   query charAt 0                     ------------------------------------------------------------------------------                 if  Character isDigit                                                         else if  Character isLetter

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Below regexs can be used to check if a string has only number or not   if  str matches      0-9        or if  str matches      D       Both conditions above will return true if String containts non-numbers  On false  string has only numbers

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It is a bad practice to involve any exception throwing handling into such a typical scenario   Therefore a parseInt   is not nice  but a regex is an elegant solution for this  but take care of the following  -fractions -negative numbers -decimal separator might differ in contries  e g      or      -sometimes it is allowed to have a so called thousand separator  like a space or a comma e g  12 324 1000 355  To handle all the necessary cases in your application you have to be careful  but this regex covers the typical scenarios  positive negative and fractional  separated by a dot     -    d    d   For testing  I recommend regexr com

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This code is already written  If you don t mind the  extremely  minor performance hit--which is probably no worse than doing a regex match--use Integer parseInt   or Double parseDouble    That ll tell you right away if a String is only numbers  or is a number  as appropriate   If you need to handle longer strings of numbers  both BigInteger and BigDecimal sport constructors that accept Strings  Any of these will throw a NumberFormatException if you try to pass it a non-number  integral or decimal  based on the one you choose  of course   Alternately  depending on your requirements  just iterate the characters in the String and check Character isDigit   and or Character isLetter

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Apache Commons Lang provides org apache commons lang StringUtils isNumeric CharSequence cs   which takes as an argument a String and checks if it consists of purely numeric characters  including numbers from non-Latin scripts   That method returns false if there are characters such as space  minus  plus  and decimal separators such as comma and dot   Other methods of that class allow for further numeric checks

[java] Java String - See if a string contains only numbers and not letters

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