Java: Regular Expressions

[] – 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.

public class ValidateInput {
    
    public static boolean validateFirstName(String firstName) {
        return firstName.matches("[A-Z][a-zA-Z]*");
    }// Jane
    
    public static boolean validateLastName(String lastName) {
        return lastName.matches("[a-zA-z]+(['-][a-zA-Z]+)*");
    }// Doe
    
    public static boolean validateAddress(String address) {
        return address.matches("\d+\s+([a-zA-Z]+|[a-zA-Z]+\s[a-zA-Z]+)");
    } //10 Boradyway or 10 Main Street
    
    public static boolean validateCity(String city) {
        return city.matches("([a-zA-Z]+|[a-zA-Z]+\s[a-zA-Z]+)");
    } //Waltham or West Newton
    
    public static boolean validateState(String state) {
        return state.matches("([a-zA-Z]+|[a-zA-Z]+\s[a-zA-Z]+)");
    } //SS
    
    public static boolean validateZip(String zip) {
        return zip.matches("\d{5}");
    } //12345
    
    public static boolean validatePhone(String phone) {
        return phone.matches("[1-9]\d{2}-[1-9]\d{2}-\d{4}");
    } //123-456-7890

}