How to get position of the first letter in a string

Question

I need to get position of the first letter in a string.

Follow a basic example. The first letter is T, So I need to know the position of T, for that I can use indexOf("T").

I would like to get the first letter by regex instead to add the letter hard-coded (T).

Thanks in advance.

public class RegexMatches {
    public static void main(String args[]) {

        String line = "000 1 This is my message";
        int first = line.indexOf("T");
        line = line.substring(first, line.length());

        System.out.println(line);
     }
}

possible duplicate of [Java: method to get position of a match in a String?](http://stackoverflow.com/questions/2615749/java-method-to-get-position-of-a-match-in-a-string) — Robin, Apr 30 '14 at 14:20
@Robin: But that question doesn't consider regex matches, does it? — Tim Pietzcker, Apr 30 '14 at 14:22
The indexOf can't receive "T" because it's a example, if the message starts with other letter it will not works. — Edson Martins, Apr 30 '14 at 14:23
@Mena please undelete your answer. It was basically correct, just don't read the group but the start index. — Thomas, Apr 30 '14 at 14:24
@TimPietzcker: my bad, should have linked to that one: [Java: method to get position of a match in a String?](http://stackoverflow.com/questions/8938498/get-the-index-of-a-pattern-in-a-string-using-regex) — Robin, Apr 30 '14 at 14:25
@BheshGurung yes, but Mena's is also correct with the minor change suggested. (And he was first to answer ;) ) — Thomas, Apr 30 '14 at 14:27

score 8 · Answer 1 · answered Apr 30 '14 at 14:22

8

If, as I interpret, you're looking for the first alphabetic character in a sentence or its index through regular expressions, here's an example:

String line = "000 1 This is my message";
Pattern p = Pattern.compile("\\p{Alpha}");
Matcher m = p.matcher(line);
if (m.find()) {
    System.out.println(m.group());
    System.out.println("At: " + m.start());
}

Output

Found: T
At: 6

answered Apr 30 '14 at 14:22

Mena

47,782
11
87
106

This doesn't work for non-english alphabets. – MA1 Sep 15 '21 at 20:27

score 8 · Accepted Answer · answered Apr 30 '14 at 14:24

8

If I read the Java docs correctly, you're looking for the start method of the match object:

String line = "000 1 This is my message";
Pattern p = Pattern.compile("\\p{L}");
Matcher m = p.matcher(line);
if (m.find()) {
    System.out.println(m.start());
}

answered Apr 30 '14 at 14:24

Tim Pietzcker

328,213
58
503
561

score 3 · Answer 3 · edited May 23 '17 at 12:25

If you don't need regex you can do it just by looping through (My reccomendation)

public int findFirstLetterPosition(String input) {
    char c;
    for (int i = 0; i < input.length(); i++) {
        c = input.charAt(i);
        if ( (c >= 'a' && c <= 'z') || (c >= 'A' || c <= 'Z') ) {
            return i;
        }
    }
    return -1; // not found
}

EDIT

In response to some comments, you could also do this less explicitly using a built in static method, and add some handling for non-ASCII characters using isLetter:

public int findFirstLetterPosition(String input) {
    for (int i = 0; i < input.length(); i++) {
        if (Character.isLetter(input.charAt(i))) {
            return i;
        }
    }
    return -1; // not found
}

You can also use isAlphabetic:

public int findFirstLetterPosition(String input) {
    for (int i = 0; i < input.length(); i++) {
        if (Character.isAlphabetic(input.charAt(i))) {
            return i;
        }
    }
    return -1; // not found
}

The latter includes some alphabetic characters from other languages which are iffy on whether to box them as characters or phrases

ref: Character.isLetter, Character.isAlphabetic

What would you do for non-ASCII characters? – Thomas Apr 30 '14 at 14:25 — Thomas, Apr 30 '14 at 14:25
Why not `if (Character.isLetter(c))`? – Elliott Frisch Apr 30 '14 at 14:31 — Elliott Frisch, Apr 30 '14 at 14:31

How to get position of the first letter in a string

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