Difference between matches() and find() in Java Regex

matches tries to match the expression against the entire string and implicitly add a ^ at the start and $ at the end of your pattern, meaning it will not look for a substring. Hence the output of this code:

public static void main(String[] args) throws ParseException {
    Pattern p = Pattern.compile("\\d\\d\\d");
    Matcher m = p.matcher("a123b");
    System.out.println(m.find());
    System.out.println(m.matches());

    p = Pattern.compile("^\\d\\d\\d$");
    m = p.matcher("123");
    System.out.println(m.find());
    System.out.println(m.matches());
}

/* output:
true
false
true
true
*/

123 is a substring of a123b so the find() method outputs true. matches() only ‘sees’ a123b which is not the same as 123 and thus outputs false.