Find all words with 3 letters with regex

问题:

I'm trying to find all words with 3 letters in a string.
So in this list

cat monkey dog mouse

I only want

cat dog

This is my expression:

^[a-zA-Z]{3}$

I tested it with different online regex tester, but none of them matched my expression.

回答1:

You should use your match with word boundaries instead of anchors:

\b[a-zA-Z]{3}\b

RegEx Demo

When you use:

^[a-zA-Z]{3}$

It means you want to match a line with exact 3 letters.

回答2:

you can use . instead of [a-zA-Z] if you want to match any character (also numbers):

 \b.{3}\b

回答3:

1. To match all words with 3 letters in a string, the pattern needs to be "\b[a-zA-Z]{3}\b"

2. The next step would be to compile your pattern.

   Pattern pattern = Pattern.compile("\\b[a-zA-Z]{3}\\b");
   

3. Use a matcher and use the find() and group() methods to print the occurrences

   for (String word : sentence) {
       Matcher matcher = pattern.matcher(word);
       while(matcher.find()) {
           System.out.println(matcher.group());
       }
   }
   

4. Your program should look something like -

   public static void main(String[] args) {
       List<String> sentence = new ArrayList<String>();
       sentence.add("cat");
       sentence.add("monkey");
       sentence.add("dog");
       sentence.add("mouse");
   
       Pattern pattern = Pattern.compile("\\b[a-zA-Z]{3}\\b");
   
       for (String word : sentence) {
           Matcher matcher = pattern.matcher(word);
           while(matcher.find()) {
               System.out.println(matcher.group());
           }
       }
   }