Why Doesn\'t My Regex Work in Java\'s String.matches()?

Regex Doesn't Work in String.matches()

Question:

A user wrote a code snippet to match strings containing only lowercase letters:

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

However, the code does not print anything, despite expecting "dkoe" as the output.

Answer:

Contrary to its name, Java's String.matches() method matches the entire input string against a regular expression. To match only a part of the string, use Pattern and Matcher instead:

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

Alternatively, if you want to match the entire string, append a to the character class in the matches() method:

if(s.matches("[a-z]+"))

Or use a complete regex pattern:

if(s.matches("^[a-z]+$"))

This will match strings containing only lowercase letters, as the ^ and $ anchors ensure that the match covers the entire input string.

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