Why Doesn\'t `String.matches()` Work as Expected with Regular Expressions?

String.matches() Doesn't Match Expected Regex

When attempting to match a specific pattern using String.matches("[a-z]"), it's surprising to find that it doesn't work as expected, even though the string contains lowercase letters.

Explanation:

The String.matches() method in Java is designed to determine if the entire input string matches the provided regular expression. In this case, the expression "[a-z]" is attempting to match a single lowercase letter. However, the code checks each string in the words array, none of which start with a lowercase letter.

Solution:

To match a pattern within a string, one should use the Pattern and Matcher classes. The Pattern class compiles the regular expression into a Matcher object, which can then be used to check for matches in the input string.

Here's a modified version of the code that uses Pattern and Matcher to find matches:

Pattern p = Pattern.compile("[a-z]+");
for(String s:words)
{
    Matcher m = p.matcher(s);
    if (m.find())
    {
        System.out.println(s);
    }
}

This code now correctly prints "dkoe".

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