Basic collation of Java regular expressions

(a) Introduction to regular expressions and grammars

1. The string class uses several methods of regular expressions:
2. Valid characters supported by regular expressions:
3. Special characters:
4. Pre-defined characters:
5. Square brackets Expression:
6. Parenthesis expression: Used to make multiple expressions into a subexpression, you can use the OR operator "|", such as a regular expression: "(AA|BB|CC)" is to match "AA", "BB", "CC" One of the three strings.
7. Boundary match:
8. Greedy, reluctant, possessive number identifiers:

(ii) Simple usage of Java regular expressions

2. Two key classes: (1) Pattern: The representation of a regular expression after it is compiled in memory. is an immutable class that can be used concurrently by multiple threads, (2) Matcher: Saves the various states involved in performing a match, and multiple Matcher objects can share a pattern object.
4. Example of a simple usage program:

   1 // Output: True 2 Pattern p = pattern.compile ("a*b"); 3 Matcher m = P.matcher ("AABZAAADAAAFBC"); 4 // Output: False

6. Common methods of the Matcher class:

7. Examples of programs:

   1  　　  Public Static voidtest1 () {2System.out.println (Pattern.matches ("A\\WB", "A_b"));//Output: True3 4Pattern p = pattern.compile ("A*b");5Matcher m = P.matcher ("AABZAAADAAAFBC");6 7System.out.println (M.matches ());//Output: False8System.out.println (M.find ());//Output: True9System.out.println (M.group ());//output: bTenSystem.out.println (M.start ());//Output: 2 OneSystem.out.println (M.end ());//Output: 3 ASystem.out.println (M.lookingat ());//Output: True -M.reset ("Zab"); -System.out.println (M.lookingat ());//Output: False the     } -  -      Public Static voidtest2 () { -Matcher m = pattern.compile ("\\w+"). Matcher ("Java is very easy!"); +  -          while(M.find ()) { +System.out.println (M.group () + "substring start position:" + m.start () + ", End position:" A+m.end ()); at         } -  -         inti = 0; -          while(M.find (i)) { -System.out.print (M.group () + "\ T"); -i++; in         } -  to         //Output: +         //starting position of the Java substring: 0, End position: 4 -         //is substring start position: 5, End position: 7 the         //very the starting position of the substring: 8, end Position: *         //Easy substring start position: 13, End Position: $         //Java Ava va A is are s very very ery ry y easy easy asy sy yPanax Notoginseng     } -  the      Public Static voidtest3 () { +string[] mails = {"[email protected]", "[email protected]", A"[Email protected]", "[email protected]" }; theString Mailregex = "\\w{3,20}@\\w+\\. (com|cn|edu|org|net|gov) "; +Pattern Mailpattern =Pattern.compile (Mailregex); -  $Matcher Mailmatcher =NULL; $  -          for(String mail:mails) { -             if(Mailmatcher = =NULL) { theMailmatcher =mailpattern.matcher (mail); -}Else {Wuyi mailmatcher.reset (mail); the             } -  WuSystem.out.println (Mail + (mailmatcher.matches)? "Yes": "No") -+ "A valid e-mail address"); About         } $  -         //Output: -         //[email protected] is a legitimate e-mail address -         //[email protected] is a legitimate e-mail address A         //[email protected] is not a valid email address +         //[email protected] is not a valid email address the  -     } $  the      Public Static voidtest4 () { theMatcher m = pattern.compile ("\\bre\\w*"). Matcher ( the"Java is real good at Inrestart and regex."); theSystem.out.println (M.replaceall ("haha")); -  in         //Output: the         //Java is haha good at inrestart and haha. the  About}

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Basic collation of Java regular expressions