Regular expression matching rules
Referring to the help documentation, there are rules define regular expressions in the Pattern class, regular expressions a clear distinction between uppercase and lowercase letters. Let's learn the rules of grammar.
Regular expression syntax rules:
Character: the X-
Meaning: represents the character x
For example: matching rule is "a" , then the content needs to match the string is "a"
Character: \\
Meaning: represents the backslash character '\'
For example: matching rule is "\\" , you need to match the contents of the string is "\"
Character: \ t
Meaning: Tabs
For example: matching rule "\ T ", then the corresponding effect is to create a space of a tab
Character: \ the n-
Meaning: newline
For example: matching rule "\ n-" , then the corresponding effect is to change the line, the next line in the original cursor position
Characters: \ r
Meaning: a carriage return
For example: matching rule is "\ r" , then the corresponding effect is the effect after the carriage return, cursor to next line
Character class: [abc]
Meaning: represents the character A , b or c
Matching rules: for example "[abc]" a, then the content is the need to match the characters a, B or character, or a character c
Character class: [^ abc]
Meaning: that in addition to representatives of A , b or c other than any character
For example: matching rule "[^ ABC]" , then the content is not required to match the characters a, or not characters b, c or not the character of any character
Character class: [A-zA-the Z]
Meaning: represents a to z or A to the Z , two letters included
For example: matching rule "[A-zA-the Z]" , it is a need to match uppercase and lowercase letters
Character class: [0-9]
Meaning: represents 0 Dao 9 numbers, including the numbers of two
For example: matching rules "[0-9]" , then you need to match a digital
Character class: [A-zA-Z ~ 0-9]
Meaning: letters or numbers or underscore representative ( ie word characters )
For example: matching rule "[A-zA-Z ~ 0-9]" , then the match is needed is a letter or a digit line or a decline in
Predefined character classes: .
Meaning: stands for any character
For example: matching rules . "" , You need to match an arbitrary character. If you wanted to use. Then, using the matching rules "\\." To achieve
Predefined character classes: \ d
Meaning: a is 0 to . 9 figures, including the two figures, corresponding to [0-9]
For example: matching rules "\ d" , then you need to match a digital
Predefined character classes: \ w
Meaning: letters or numbers or underscores representative ( i.e., word characters ) , equivalent to [a-zA-Z_0-9]
For example: matching rule "\ W" ,, it is required to match a number or a letter or a decline in line
Boundary matcher: ^
Meaning: represents the beginning of the line
For example: matching rule ^ [abc] [0-9] $ , then the content needs to be matched from the beginning [abc] this position is equivalent to a left double quotation mark
Boundary matcher: $
Meaning: represents the end of the line
For example: matching rule ^ [abc] [0-9] $ , then the content needs to match [0-9] this end, the equivalent of closing double quotation mark
Boundary matcher: \ b
Meaning: represents the word boundary
For example: matching rule "\ b [ABC] \ b" , it represents a non-desired word characters left and right letter a or b, or c ( [a-zA-Z ~ 0-9] )
Quantifier: the X-?
Meaning: represents the X occur once or even once
For example: matching rule is "a?" , Then you need to match the contents of a character is a, or a not a
Quantifier: the X-*
Meaning: stands for X appear zero or more times
For example: matching rule is "a *" , you need to match the contents of more than one character is a, or a not a
Quantifiers: the X-+
Meaning: it stands for X one or more occurrences
For example: matching rule "a +" , then the need to match the contents of the plurality of characters a, a, or a
Quantifier: X-n-{}
Meaning: stands for X appear exactly n times
For example: matching rule "{a}. 5" , then the need to match the contents of five characters a
Quantifier: X-n-{,}
Meaning: represents the X appears at least n times
For example: matching rule ". 5 {a,}" , then the need to match the content is a minimum of five characters
Quantifier: X-n-{,} m
Meaning: represents the X appears at least n times, but not more than m times
For example: matching rule "a {5,8}" , then there is a need to match the contents of between five to eight characters in a character a
Regular expression syntax rules
* A: 正则表达式语法规则
* a: 字符
* x 代表的是字符x
* \\ 代表的是反斜线字符'\'
* \t 代表的是制表符
* \n 代表的是换行符
* \r 代表的是回车符
* b: 字符类
* [abc] a、b 或 c（简单类）
* [^abc] 任何字符，除了 a、b 或 c（否定）
* [a-zA-Z] a到 z 或 A到 Z，两头的字母包括在内（范围）
* [0-9] 0到9的字符都包括
* [a-zA-Z_0-9] 代表的字母或者数字或者下划线(即单词字符)
* c: 预定义字符类
* . 任何字符。
* \d 数字：[0-9]
* \w 单词字符：[a-zA-Z_0-9]如"com.itheima.tests"/finish
* d: 边界匹配器
* ^ 代表的是行的开头
* $ 代表的是行的结尾
* \b 代表的是单词边界
* e: 数量词
* X? X，一次或一次也没有
* X* X，零次或多次
* X+ X，一次或多次
* X{n} X，恰好 n 次
* X{n,} X，至少 n 次
* X{n,m} X，至少 n 次，但是不超过 m 次
