# Notes

# Regex

Java Subexpression	Matches
`^`	Matches beginning of line. 匹配行首。
`$`	Matches end of line. 匹配行尾。
`.`	Matches any single character except newline. Using m option allows it to match newline as well. 匹配除换行符以外的任何单个字符。使用 m 选项还可以使其与换行符匹配。
`[...]`	Matches any single character in brackets. 匹配括号中的任何单个字符。
`[^...]`	Matches any single character not in brackets. 匹配括号中没有的任何单个字符。
`\A`	Beginning of entire string 整个字符串的开头
`\z`	End of entire string 整个字符串的结尾
`\Z`	End of entire string except allowable final line terminator. 整个字符串的结尾，但允许的最后一行终止符除外。
`re*`	Matches 0 or more occurrences of preceding expression. 匹配 0 个或多个出现的前一个表达式。
`re+`	Matches 1 or more of the previous thing. 匹配上一项或多项。
`re?`	Matches 0 or 1 occurrence of preceding expression. 匹配 0 或 1 个出现的前一个表达式。
`re{ n}`	Matches exactly n number of occurrences of preceding expression. 精确匹配前一个表达式的 n 次出现。
`re{ n,}`	Matches n or more occurrences of preceding expression. 匹配 n 个或多个出现的前一个表达式。
`re{ n, m}`	Matches at least n and at most m occurrences of preceding expression. 至少匹配 n 个并且最多匹配 m 个先前的表达式。
`a\|b`	Matches either a or b. 匹配 a 或 b。
`\w`	Matches word characters. 匹配单词字符。
`\W`	Matches nonword characters. 匹配非单词字符。
`\s`	Matches whitespace. Equivalent to `[\t\n\r\f]` . 匹配空格。等效于 `[\t\n\r\f]` 。
`\S`	Matches nonwhitespace. 匹配非空格。
`\d`	Matches digits. Equivalent to `[0-9]` . 匹配数字。相当于 `[0-9]` 。
`\D`	Matches nondigits. 匹配非数字。
`\A`	Matches beginning of string. 匹配字符串的开头。
`\Z`	Matches end of string. If a newline exists, it matches just before newline. 匹配字符串的结尾。如果存在换行符，则匹配换行符。
`\z`	Matches end of string. 匹配字符串的结尾。
`\b`	Matches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets. 放在方括号内时匹配单词边界。放在方括号内时，匹配退格键（0x08）。

Referece sites:
http://www.regexr.com
http://www.tutorialspoint.com/java/java_regular_expressions.htm

# demo

EmailValidator.java

	import java.util.regex.Matcher;
	import java.util.regex.Pattern;

	public class EmailValidator {
	// Regex pattern to valid email address
	private static final String EMAIL_REGEX=
	"^[\\w-\\+]+(\\.[\\w]+)@[\\w-]+(\\.[\\w]+)(\\.[a-z]{2,})$";
	//static Pattern object, since pattern is fixed
	private static Pattern pattern;
	//non-static Matcher object because it's created from the input String
	private Matcher matcher;

	public EmailValidator(){
	//initialize the Pattern object
	pattern = Pattern.compile(EMAIL_REGEX, Pattern.CASE_INSENSITIVE);
	}
	/**
	* This method validates the input email address with EMAIL_REGEX pattern
	* @param email
	* @return boolean
	*/
	public boolean validateEmail(String email){
	matcher = pattern.matcher(email);
	return matcher.matches();
	}
	}

	public class EmailValidatorTest {

	// list of valid email addresses
	private static final String[] validEmailIds = new String[] {
	"papadev@yahoo.com",
	"papadev-100@yahoo.com", "papadev.100@yahoo.com",
	"papadev111@papadev.com", "papadev-100@papadev.net",
	"papadev.100@papadev.com.au", "papadev@1.com",
	"papadev@gmail.com.com", "papadev+100@gmail.com",
	"papadev-100@yahoo-test.com", "papadev_100@yahoo-test.ABC.CoM" };

	// list of invalid email addresses
	private static final String[] invalidEmailIds = new String[] { "papadev",
	"papadev@.com.my",
	"papadev123@gmail.a", "papadev123@.com", "papadev123@.com.com",
	".papadev@papadev.com", "papadev()@gmail.com", "papadev@%.com",
	"papadev..2002@gmail.com", "papadev.@gmail.com",
	"papadev@papadev@gmail.com", "papadev@gmail.com.1a" };

	private static EmailValidator emailValidator;

	public static void main(String args[]){
	emailValidator = new EmailValidator();
	for (String temp : validEmailIds) {
	boolean valid = emailValidator.validateEmail(temp);
	System.out.println("Email ID "+temp+" is valid? " + valid);
	}
	System.out.println("\n\n");
	for (String temp : invalidEmailIds) {
	boolean valid = emailValidator.validateEmail(temp);
	System.out.println("Email ID "+temp+" is valid? " + valid);
	}
	}
	}

Email ID papadev@yahoo.com is valid? true
Email ID papadev-100@yahoo.com is valid? true
Email ID papadev.100@yahoo.com is valid? true
Email ID papadev111@papadev.com is valid? true
Email ID papadev-100@papadev.net is valid? true
Email ID papadev.100@papadev.com.au is valid? true
Email ID papadev@1.com is valid? true
Email ID papadev@gmail.com.com is valid? true
Email ID papadev+100@gmail.com is valid? true
Email ID papadev-100@yahoo-test.com is valid? true
Email ID papadev_100@yahoo-test.ABC.CoM is valid? true
 
Email ID papadev is valid? false
Email ID papadev@.com.my is valid? false
Email ID papadev123@gmail.a is valid? false
Email ID papadev123@.com is valid? false
Email ID papadev123@.com.com is valid? false
Email ID .papadev@papadev.com is valid? false
Email ID papadev()*@gmail.com is valid? false
Email ID papadev@%*.com is valid? false
Email ID papadev..2002@gmail.com is valid? false
Email ID papadev.@gmail.com is valid? false
Email ID papadev@papadev@gmail.com is valid? false
Email ID papadev@gmail.com.1a is valid? false

# Review

Regular Expressions (RegEx) - For text searching & manipulation

Set up a patten to match given tasks for given strings below.

String/phrase	Task	Your Pattern
"cat cat cat cattie cat"	Find Cat occurrences	`"\\bcat\\b"` note use of the added ( \ ) character used as an escape sequence
doggy	Find dog	`dog`
Apple123	Must start with Apple	`[Apple].*`
Apple123	Must NOT start with Apple	`[^Apple].*`
Apple123	Must start with Apple or apple	`[Apple\|apple].*`