How to check if a string is numeric

Question

I have a gpa program  and it works with the equalsIgnoreCase   method which compares two strings  the letter  a  to the user input  which checks if they put  a  or not  But now I want to add an exception with an error message that executes when a number is the input  I want the program to realize that the integer input is not the same as string and give an error message  Which methods can I use to compare a type String variable to input of type int  and throw exception

User · Answer

I wrote this little method lastly in my program so I can check if a string is numeric or at least every single char is a number   private boolean isNumber String text       if text    null     text equals                char   characters   text toCharArray            for  int i   0  i  lt  text length    i                  if  characters i   lt  48    characters i   gt  57                  return false                      return true

User · Answer

You can use Character isDigit char ch  method or you can also use regular expression   Below is the snippet   public class CheckDigit    private static Scanner input   public static void main String   args         System out print  Enter a String         input   new Scanner System in       String str   input nextLine         if  CheckString str             System out println str     is numeric          else           System out println str    is not numeric             public static boolean CheckString String str        for  char c   str toCharArray              if   Character isDigit c               return false            return true

User · Answer

Use this   public static boolean isNum String strNum        boolean ret   true      try            Double parseDouble strNum         catch  NumberFormatException e            ret   false            return ret

User · Answer

Use below method   public static boolean isNumeric String str          try             double d   Double parseDouble str             catch NumberFormatException nfe              return false            return true        If you want to use regular expression you can use as below   public static boolean isNumeric String str      return str matches  -   d       d          match a number with optional  -  and decimal

User · Answer

If you are allowed to use third party libraries  suggest the following   https   commons apache org proper commons-lang javadocs api-2 6 org apache commons lang math NumberUtils html  NumberUtils isDigits str String  boolean NumberUtils isNumber str String  boolean

User · Answer

Many options explored at http   www coderanch com t 405258 java java String-IsNumeric  One more is   public boolean isNumeric String s          return s    null  amp  amp  s matches   -     d       d             Might be overkill but Apache Commons NumberUtils seems to have some helpers as well

User · Answer

public static boolean isNumeric String string        if  string    null    string isEmpty              return false            int i   0      int stringLength   string length        if  string charAt 0      -             if  stringLength  gt  1                i              else               return false                      if   Character isDigit string charAt i                   Character isDigit string charAt stringLength - 1              return false            i        stringLength--      if  i  gt   stringLength            return true            for    i  lt  stringLength  i              if   Character isDigit string charAt i                    amp  amp  string charAt i                        return false                      return true

User · Answer

Simple method   public boolean isBlank String value        return  value    null    value equals        value equals  null      value trim   equals           public boolean isOnlyNumber String value        boolean ret   false      if   isBlank value             ret   value matches    0-9                 return ret

User · Answer

Here s how to check if the input contains a digit   if  input matches      d               there s a digit somewhere in the input string

User · Answer

You can also use ApacheCommons StringUtils isNumeric - http   commons apache org proper commons-lang javadocs api-2 6 org apache commons lang StringUtils html isNumeric java lang String

User · Answer

To check for all int chars  you can simply use a double negative   if   searchString matches    0-9              0-9    checks to see if there are any characters that are not integer  so the test fails if it s true  Just NOT that and you get true on success

[java] How to check if a string is numeric?

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