How to know if a String only contains 0 to 9 and no other characters

Question

I am new here and I have a problem with a code.

I have a String of 5 characters, and this is what I've come up with

public static boolean isNumber(String strng) {
    return (strng.contains("[0-9]+"));
}

public static void main(String[] args) {
     String strng; 
     Scanner strong = new Scanner(System.in);


while (isNumber(dato) == true && dato.length() != 5){
        System.out.println("Isnt a correct id number");
        strng = strong.nextLine();

    }

But with this I can introduce a dot or a semi-colon, I tried with [a-zA-Z]+ and the boolean in false but isn't work I'm searching only for numbers from 0 to 9.

Any clue for this?

`strng.contains("[0-9]+")` returns `true` for inputs that has digits, but doesn't check that it has *only* digits. — Maroun, May 19 '15 at 13:40
@MarounMaroun No, it will not. `strng.contains("[0-9]+")` returns `true` only if the string literally contains `[0-9]+`. The `contains` method does not take a regular expression. — Jesper, May 19 '15 at 13:46
@Jesper You're right. `matches` accepts `CharSequence` and not a regex string. Thanks. — Maroun, May 19 '15 at 13:47

Konstantin Yovkov · Answer 1 · 2015-05-19T13:57:58.660

7

strng.contains("[0-9]+") should rather be strng.matches("[0-9]+")

This will test your strng to have one or more digits.

If you want your string to match exactly five digits, then you'll have to use the "[0-9]{5}" pattern.

edited May 19 '15 at 13:57

answered May 19 '15 at 13:40

Konstantin Yovkov

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Hi! thanks for the reply! i tried matches too but it only see if the string have a number and not if it hasnt other character so i can introduce "1234." and the string has numbers but the dot isnt good – Mathew Euler May 19 '15 at 13:42
3

It's a good practice to *explicitly* call `Pattern.compile` before passing the regex to `matches`. – Maroun May 19 '15 at 13:44
True. Especially for more complex patterns. – Konstantin Yovkov May 19 '15 at 13:44
@MathewEuler "*but the dot isnt good*" is that a problem? Based on your title you only wanted "*0-9 and no other characters*". – Pshemo May 19 '15 at 13:49
Exactly, i only have to be able to 0-9 digits and nothing else, the problem is that with contains or matches ([0-9]+{5}) isnt working – Mathew Euler May 19 '15 at 13:56
How about with `"[0-9]{5}"`? – Konstantin Yovkov May 19 '15 at 13:57

score 5 · Answer 2 · answered May 19 '15 at 13:43

5

You can check the content and the length with your regex:

strng.matches("[0-9]{5}")

This will return true for strings of exactly 5 characters, containing only digit characters.

answered May 19 '15 at 13:43

Armand

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How to know if a String only contains 0 to 9 and no other characters

2 Answers2