How to check a string contains only int in JAVA?

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!

Seems like a homework question to me... add a homework tag if so — recursion.ninja, Nov 18 '12 at 21:16
@A.R.S. I did not know that the homework tag was depreciated ;) — recursion.ninja, Nov 18 '12 at 21:32

Nitin Chhajer · Accepted Answer · 2012-11-18T21:16:05.927

8

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.

edited Nov 18 '12 at 21:16

answered Nov 18 '12 at 21:10

Nitin Chhajer

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arshajii · Answer 2 · 2012-11-18T21:41:46.203

4

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}+".

edited Nov 18 '12 at 21:41

answered Nov 18 '12 at 21:09

arshajii

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That good for number validation, but integer has also some length. – Damian Leszczyński - Vash Nov 18 '12 at 21:14
No. What I meant is integer is shorten than long. `+` is only responsible for that empty string is not treated as valid. – Damian Leszczyński - Vash Nov 18 '12 at 21:22

How to check a string contains only int in JAVA?

2 Answers2