Java starts from zero 32 (regular expression)

First, why have regular regular expressions can easily match the data, you can perform more complex string verification, split, replace the function. For example, it is now required to determine whether a string is composed of numbers, and there are two ways to do this: do not use regular completion two,Pattern, Matcher classIf you want to apply a regular expression to your program, you must rely on the pattern class and the Matcher class, which are defined in the Java.util.regex package. Two classes. The main function of the pattern class is to write the regular specification, and the Matcher class is the execution specification, which verifies whether a string conforms to its specification. Common Regular Rules

No.	Specification	Describe	No.	Specification	Describe
1	\\	Represents a backslash (\) character	2	\ t	Represents a tab character
3	\ n	Represents a line break	4	[ABC]	Character A, b, or C
5	[^ABC]	Any character except A, B, c	6	[A-za-z0-9]	denoted by letters, numbers
7	\d	Represents a number	8	\d	Represents non-numeric
9	\w	Denotes letters, numbers, underscores	10	\w	Denotes non-alphabetic, numeric, underline
11	\s	Represents all whitespace characters (line breaks, spaces, and so on)	12	\s	Represents all non-whitespace characters
13	^	The beginning of the line	14	$	End of Line
15	.	Match any character except line break

  Quantity Representation (x represents a set of specifications)

No.	Specification	Describe	No.	Specification	Describe
1	X	Must appear once	2	X?	can occur 0 or 1 times
3	x*	can occur 0 times, 1 times or more	4	x+	Can occur 1 or more times
5	X{n}	Must appear n times	6	X{n,}	Must appear more than n times
7	X{N,M}	Must appear n~m times

logical operators (X, y represent a set of specifications)

No.	Specification	Describe	No.	Specification	Describe
1	Xy	x specification followed by Y specification	2	X | Y	x specification or Y specification
3	X	As a capture group specification

common methods of pattern class

No.	Method	Type	Describe
1	public static Pattern compile (String regex)	Ordinary	Specifying regular expression rules
2	Public Matcher Matcher (charsequence input)	Ordinary	Returns an instance of the Matcher class
3	Public string[] Split (charsequence input)	Ordinary	String splitting

in the pattern class, if you want to get an instance of the pattern class, you must call the compile () method. Common methods of Matcher class

No.	Method	Type	Describe
1	public Boolean matches ()	Ordinary	Perform validation
2	public string ReplaceAll (string replacement)	Ordinary	String substitution

If you want to verify that a string conforms to the specification, you can use the Matcher class three, the regular validation 3.1, the validation character composition

 PackageCom.pb.demo2;ImportJava.util.regex.Pattern; Public classRegexDemo1 { Public Static voidMain (string[] args) {String str= "1234567890";//the declaration string is made up of numbers//using regular validation        if(Pattern.compile ("[0-9]+"). Matcher (str). Matches ()) {System.out.println ("Numbers. "); }Else{System.out.println ("Not all are made up of numbers. "); }            }}

3.2. Verify whether a string is a valid date format

 PackageCom.pb.demo2;ImportJava.util.regex.Matcher;ImportJava.util.regex.Pattern;/** Verify if a string is a valid date format*/ Public classRegexDemo2 { Public Static voidMain (string[] args) {String str= "1983-07-23"; String Pat= "\\d{4}-\\d{1,2}-\\d{1,2}";//Defining RulesPattern P=pattern.compile (PAT);//instantiating a pattern class objectMatcher M=p.matcher (str);//Verify string content is legitimate//using regular validation        if(M.matches ()) {System.out.println ("Date format is legal!!"); }Else{System.out.println ("Date format is not legal!!"); }                    }}

3.3. Split the string according to the number of the string

 PackageCom.pb.demo2;ImportJava.util.regex.Matcher;ImportJava.util.regex.Pattern;/** Split the string according to the number of the string*/ Public classRegexDemo2 { Public Static voidMain (string[] args) {String str= "A1b22c333d4444e55555f6g77"; String Pat= "\\d+";//define a split rulePattern P=pattern.compile (PAT);//instantiating the pattern classString [] ss=p.split (str);//split into string arrays//Traverse         for(String s:ss) {System.out.print (s+ "\ T"); }            }}

Results:

A    B    C    D    E    F    G    

3.4. Replace Operation

 PackageCom.pb.demo2;ImportJava.util.regex.Matcher;ImportJava.util.regex.Pattern;/** Replace the string with the number of the string*/ Public classRegexDemo4 { Public Static voidMain (string[] args) {String str= "A1b22c333d4444e55555f6g77"; String Pat= "\\d+";//define the rules for substitutionPattern P=pattern.compile (PAT);//instantiating the pattern classMatcher M=p.matcher (str);//instantiate the Matcher classString Newstrirng=m.replaceall ("_");//the character to replaceSystem.out.println (NEWSTRIRNG); }}

Results:

A_b_c_d_e_f_g_

3.5. Email Verification

 PackageCom.pb.demo2;ImportJava.util.Scanner;ImportJava.util.regex.Matcher;ImportJava.util.regex.Pattern;/** Email is legal*/ Public classRegexDemo5 { Public Static voidMain (string[] args) {Scanner input=NewScanner (system.in); //String pat= "^[a-za-z0-9_][email protected][a-za-z0-9_]+ (. [ a-za-z_]{2,3}) {1,2}$ ";String regex= "^\\[email protected]\\w+ (. [ a-za-z_]{2,3}) {1,2}$ "; System.out.println ("Enter mailbox:"); String Email=Input.nextline (); Pattern P=Pattern.compile (regEx); Matcher m=p.matcher (email); if(M.matches ()) {System.out.println ("Legal Email!! "); }Else{System.out.println ("The mailbox is illegal!! "); }            }}

Fourstring support for regular expressionsThe following three methods are available in the string class to support a regular operation

No.	Method	Type	Describe
1	Public boolean matches (String regex)	Ordinary	String match
2	public string ReplaceAll (string regex,string replacement)	Ordinary	String substitution
3	Public string[] Split (String regex)	Ordinary	String splitting

Java starts from zero 32 (regular expression)