How to check a string contains only int in JAVA? [duplicate]

Question

I hope to write a small method to do the following things: For example, the string a = "a123", then the method should return fulse; the string b = "111", it should return true. It means only the string is an int, it should return true, all the other cases should return false. Does anyone can help me? Thank you!

Answer 1

You can use Integer.parseInt(integerString);

public boolean isInteger(String integerString){

   try{
      Integer.parseInt(integerString);
      return true;
   } catch (NumberFormatException nfe) {
      return false;
   }
}

a NumberFormatException means parsing will not be successful hence the String is not an integer.

Answer 2

If you meant you wanted a string that's composed only of the digits 0-9 (and with arbitrary length) you can just use the regular expression "\\d+", i.e. str.matches("\\d+").

If you want to take into account positive and negative signs you could use "[+-]?\\d+".

If you're considered with length (the primitive int typo can't have more than 10 digits) you could use "[+-]?\\d{1,10}+".