Regex doesn't work in String.matches()

I have this small piece of code

String[] words = {"{apf","hum_","dkoe","12f"}; for(String s:words) { if(s.matches("[a-z]")) { System.out.println(s); } } 

Supposed to print

dkoe 

but it prints nothing!!

9 Answers

Welcome to Java's misnamed .matches() method... It tries and matches ALL the input. Unfortunately, other languages have followed suit :(

If you want to see if the regex matches an input text, use a Pattern, a Matcher and the .find() method of the matcher:

Pattern p = Pattern.compile("[a-z]"); Matcher m = p.matcher(inputstring); if (m.find()) // match 

If what you want is indeed to see if an input only has lowercase letters, you can use .matches(), but you need to match one or more characters: append a + to your character class, as in [a-z]+. Or use ^[a-z]+$ and .find().

[a-z] matches a single char between a and z. So, if your string was just "d", for example, then it would have matched and been printed out.

You need to change your regex to [a-z]+ to match one or more chars.

String.matches returns whether the whole string matches the regex, not just any substring.

java's implementation of regexes try to match the whole string

that's different from perl regexes, which try to find a matching part

if you want to find a string with nothing but lower case characters, use the pattern [a-z]+

if you want to find a string containing at least one lower case character, use the pattern .*[a-z].*

Used

String[] words = {"{apf","hum_","dkoe","12f"}; for(String s:words) { if(s.matches("[a-z]+")) { System.out.println(s); } } 

I have faced the same problem once:

Pattern ptr = Pattern.compile("^[a-zA-Z][\\']?[a-zA-Z\\s]+$"); 

The above failed!

Pattern ptr = Pattern.compile("(^[a-zA-Z][\\']?[a-zA-Z\\s]+$)"); 

The above worked with pattern within ( and ).

Your regular expression [a-z] doesn't match dkoe since it only matches Strings of lenght 1. Use something like [a-z]+.

you must put at least a capture () in the pattern to match, and correct pattern like this:

String[] words = {"{apf","hum_","dkoe","12f"}; for(String s:words) { if(s.matches("(^[a-z]+$)")) { System.out.println(s); } } 

You can make your pattern case insensitive by doing:

Pattern p = Pattern.compile("[a-z]+", Pattern.CASE_INSENSITIVE);