[] – 只匹配单个字符
[枚举若干字符]：范围为所列字符。E.g. [aeiou] == a,e,i,o,u都可匹配。
[起点-终点]：范围为给定区间。
E.g.
[A-Y] == 大写字母A~Y都可匹配；
[A-Za-z] == 所有大写字母和小写字母都可匹配；
[A-z] == 大写A到小写z之间所有值，包括[,|等符号。
() – 组合
|：操作符左右任取其一。E.g. Hi (John|Jane)==匹配Hi John或Hi Jane。
Predefined Character Classes
| Character | Matches | Character | Matches |
| \d | any digit | \D | any nondigit |
| \w | any word character | \W | any nonword character |
| \s | any white-space character | \S | any non-whitespace character |
\\d == 1或以上任意长度的数字串；（加在\d前的第一个\用于取消第二个\的转义）
\\s == 1或以上任意长度的空格串；
… etc。
Quantifiers
| Quantifier | Matches |
| * | Matches zero or more occurrences of the pattern. |
| + | Matches one or more occurrences of the pattern. |
| ? | Matches zero or one occurrences of the pattern. |
| {n} | Matches exactly n occurrences. |
| {n,} | Matches at least n occurrences. |
| {n,m} | Matches between n and m (inclusive) occurrences. |
*：操作符前面紧接的pattern出现任意多次，可匹配空串。E.g. A, AAA都可匹配A*。
+：操作符前面紧接的pattern出现1或以上任意多次，不能匹配空串。E.g. A, AAA都可匹配A+，空串不能。
All quantifiers are greedy – will match as many occurrences as possible as long as the match is still successful.
But an ? following the quantifier can make it lazy (reluctant) -- it then will match as few occurrences as possible.
e.g.
1 public class ValidateInput { 2 3 public static boolean validateFirstName(String firstName) { 4 return firstName.matches("[A-Z][a-zA-Z]*"); 5 }// Jane 6 7 public static boolean validateLastName(String lastName) { 8 return lastName.matches("[a-zA-z]+(['-][a-zA-Z]+)*"); 9 }// Doe10 11 public static boolean validateAddress(String address) {12 return address.matches("\\d+\\s+([a-zA-Z]+|[a-zA-Z]+\\s[a-zA-Z]+)");13 } //10 Boradyway or 10 Main Street14 15 public static boolean validateCity(String city) {16 return city.matches("([a-zA-Z]+|[a-zA-Z]+\\s[a-zA-Z]+)");17 } //Waltham or West Newton18 19 public static boolean validateState(String state) {20 return state.matches("([a-zA-Z]+|[a-zA-Z]+\\s[a-zA-Z]+)");21 } //SS22 23 public static boolean validateZip(String zip) {24 return zip.matches("\\d{5}");25 } //1234526 27 public static boolean validatePhone(String phone) {28 return phone.matches("[1-9]\\d{2}-[1-9]\\d{2}-\\d{4}");29 } //123-456-789030 31 }