How to check a string starts with numeric number

Question

I have a string which contains alphanumeric character   I need to check whether the string is started with number   Thanks

User · Answer

Sorry I didn t see your Java tag  was reading question only  I ll leave my other answers here anyway since I ve typed them out   Java  String myString    9Hello World    if   Character isDigit myString charAt 0           System out println  String begins with a digit        C     string myString    2Hello World     if  isdigit  myString 0           printf  String begins with a digit        Regular expression    b 0-9    Some proof my regex works  Unless my test data is wrong

User · Answer

System out println Character isDigit mystring charAt 0      EDIT  I searched for java docs  looked at methods on string class which can get me 1st character  amp  looked at methods on Character class to see if it has any method to check such a thing   I think  you could do the same before asking it   EDI2  What I mean is  try to do things  read find  amp  if you can t find anything - ask  I made a mistake when posting it for the first time  isDigit is a static method on Character class

User · Answer

This should work   String s    123foo   Character isDigit s charAt 0

User · Answer

I think you ought to use a regex    import java util regex     public class Test     public static void main String   args        String neg    -123abc       String pos    123abc       String non    abc123              I m not sure if this regex is too verbose  but it should be            clear  It checks that the string starts with either a series            of one or more digits    OR a negative sign followed by 1 or            more digits  Anything can follow the digits  Update as you need            for things that should not follow the digits or for floating            point numbers                  Pattern pattern   Pattern compile      d    -  d            Matcher matcher   pattern matcher neg       if matcher matches              System out println  matches negative number              matcher   pattern matcher pos       if  matcher matches              System out println  positive matches              matcher   pattern matcher non       if   matcher matches              System out println  letters don t match  -                      You may want to adjust this to accept floating point numbers  but this will work for negatives  Other answers won t work for negatives because they only check the first character  Be more specific about your needs and I can help you adjust this approach

User · Answer

Use a regex like   d

User · Answer

See the isDigit char ch  method   https   docs oracle com javase 1 5 0 docs api java lang Character html  and pass it to the first character of the String using the String charAt   method   Character isDigit myString charAt 0

[java] How to check a string starts with numeric number?

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