Not to introduce regex grammar(If you want to know, you search it.), but some key points about using java regex.
1. How to use regex in Java?
String s1 = "ab12cd34ef";
String pattern = "(\\d+)([a-z]+)";
Pattern p = Pattern.compile(pattern); // First step: Pattern compile regex.
Matcher m = p.matcher(s1); // Second step: matcher the str.
while (m.find()) { // must find() before any group().
System.out.println(m.group()); //== group(0). output: 12cd \n 34ef.
//System.out.println(m.group(1)); //output: 12 \n 34. The first ().
//System.out.println(m.group(2)); //output: cd \n ef. The second ().
}
2. String matches()
// Show code first.
String s = "ab12cd34";
boolean b = s.matches("[a-z]+\\d+[a-z]{0,}\\d+"); // b is true.
boolean b1 = s.matches("[a-z]+\\d+"); // b1 is false.
// s.matches() is to match the whole string.
So what happened in matches() ?
s.matches(String regex) -> return Pattern.matches(regex, this).
----
Pattern.matches(regex, this) ->
Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(this); // this means the string itself.
return m.matches();
----
m.matches() -> return match(from, ENDANCHOR);
// ENDANCHOR = 1, which means to match all the input.
So in String.matches(String regex), regex match all the string.
