Basic grammar
1. Choose
| The vertical bar symbol represents selection (that is, union) and has the lowest priority. For example, "aaa | bbb" can match aaa or bbb.
2. Limited quantity
The quantity qualifier after a character is used to limit the number of characters allowed in the preceding character.
The most common quantity qualifiers include "+", "?" And "*" (unqualified quantity means it appears once and only once):
(1) The + sign means that the preceding character must appear at least once. (1 or more times).
For example, "goo + gle" can match google, gooogle, goooogle, etc .;
(2) ? The question mark indicates that the preceding character can only appear once at most. (0 times, or 1 time).
For example: "colou? R" can match color or colour;
(3) * The asterisk indicates that the preceding character may not appear, or may appear one or more times. (0 times, or 1 time, or multiple times).
For example, "0 * 42" can match 42, 042, 0041, 00042, etc.
3. Expression rules
(1) ^ Start position of matching string
(2) $ matches the end position of the string
Case:
String s1 = "111223abc";
String regex = "^[0-9]+abc$";
boolean b = s1.matches(regex);
System.out.println(b);(3) {n} n is a non-negative integer. Match n times
Example: o {2} can match food, not Bob.
(4) {n,} n is a non-negative integer. Match n times
Example: [o {2,}]
Cannot match "o" in "Bob", but can match all o in "foooood".
"o {1,}" is equivalent to "o +"
"o {0,}" is equivalent to "o *".
(5) {n, m} m and n are non-negative integers, where n <= m. Match at least n times and at most m times.
(6) x represents the character x
Example: The matching rule is "a" , then the content of the string to be matched is "a".
(7) [abc] character set, matching any one of the characters contained.
Example: "[abc]" , the matched content is one of character a, or character b, or character c
Case: Match mobile phone number
/匹配手机号
//长度11位，开头为1，第二个数字是3、7、5、8
String regex4="1[3758][0-9]{9}";
Scanner sc=new Scanner(System.in);
System.out.println("请输入手机号：");
String number=sc.next();
boolean result=number.matches(regex4);
if(result==true)
System.out.println("手机号匹配！");
else
System.out.println("手机号不匹配！");(8) [^ abc] Excluded character set, which means any character except a , b or c
(9) [a-zA-Z] matches a to z or A to Z , the two letters are included
(10) [0-9] matches 0 to 9 digits, including the two digits
(11) [a-zA-Z_0-9] matches letters or numbers or underscores ( ie word characters )
(12) . (Dot) matches any single character except "\ n". If you want to use., Use the matching rule "\\." To achieve
(13) \ d matches a numeric character. Equivalent to [0-9].
(14) \ w matches any word character including underscores. Equivalent to "[A-Za-z0-9_]".
(15) \ b matches a word boundary, that is, the position between the word and the space.
For example, "er \ b" can match "er" in "never", but not "er" in "verb".
Case: Matching mailbox
String regex="[a-zA-Z_0-9]+@[a-zA-Z_0-9]+(\\.[a-zA-Z_0-9]+)+";
System.out.println("[email protected]".matches(regex));
