Seventh Week assignment

How do I use regular expressions to check strings?

such as: Check whether the string conforms to the mailbox rules;

Checks if the string conforms to a number greater than or equal to zero;

The basic rules for regular expressions are as follows:

Character
X	Character x
\\	Backslash character
/ N	Characters with octal value 0 n (0 <= n <= 7)
/ nn	Character nn with octal value 0 (0 <= n <= 7)
/ Mnn	Characters with octal value 0 mnn(0 <= m <= 3, 0 <= n <= 7)
\x hh	Character hh with hexadecimal value of 0x
\u HHHH	Character with hexadecimal value of 0x hhhh
\ t	tab (' \u0009 ')
\ n	New lines (line break) (' \u000a ')
\ r	Carriage return character (' \u000d ')
\f	Page break (' \u000c ')
\a	Alarm (Bell) character (' \u0007 ')
\e	Escape character (' \u001b ')
\c x	The control that corresponds to x
Character class
[ABC]	a,b or C(Simple Class)
[^ABC]	Any character except a,b , or C(negation)
[A-za-z]	a to z or a to z, the letters at both ends are included (range)
[A-d[m-p]]	a to D or m to p:[a-dm-p](set)
[A-z&&[def]]	d,e or F(intersection)
[A-Z&&[^BC]]	a to Z, except for b and C:[ad-z](minus)
[A-z&&[^m-p]]	a to z, not m to p:[a-lq-z](minus)
Predefined character classes
.	Any character (may or may not match the Terminator)
\d	Numbers:[0-9]
\d	Non-numeric: [^0-9]
\s	whitespace characters:[\t\n\x0b\f\r]
\s	Non-whitespace characters:[^\s]
\w	Word character:[a-za-z_0-9]
\w	Non-word characters:[^\w]

Greedy number of words
X ?	X, not once or once
X *	X, 0 or more times
X +	X, one or more times
X {n}	X, exactly n times
X {n,}	X, at least n times
X {n,m}	X, at least n times, but not more than m Times

Typically, a double slash indicates that the string is a regular expression, while the ^ represents the beginning and $ means the end, such as/^.....$/

Whether the string conforms to the mailbox rule:/^\[email protected]\w+ (\.\w+) +$/

\w as above table: Word characters [a-za-z_0-9], \w+: Represents one or more word characters

Plus @, then one or more, \. '. ' character, so go on

whether a string conforms to a numeric rule greater than or equal to zero: /^ [1-9]\d* (\.\d+)? | 0 (\.\d+)? $/

[1-9]: Indicates that the first number is 1-9

\d: Represents a number, \d*: 0 or more digits behind

(\.\d+)?: Represents the number after the decimal point, as well as one or

|: means "or".

Note that in Java the string needs to be escaped, all requiring two backslashes \ \, as /^ [1-9]\\d* (\\.\\d+)? | 0 (\\.\\d+)? $/

above is use regular expressions to check strings

SELECT

orders.*,

User.username,

User.sex,

User.address

From

Orders

USER

WHERE orders.user_id = user.id

Seventh Week assignment