[Java learning notes] Regular Expression

Author: gnuhpc
Source: http://www.cnblogs.com/gnuhpc/

1. Introduction:

Regular Expressions are an important tool for Java to process strings and texts.

Java. util. RegEx. pattern matching class: matches the abstract results expressed by a string in a pattern.

Java. util. RegEx. matcher pattern class: used to represent a compiled regular expression.

 

2. Example

Import java. util. RegEx. pattern;

Public class regexdemo1 {
Public static void main (string Arg []) {
String expr;
String STR;

Expr = "P. t ";
STR = "pot ";
Boolean B = pattern. Matches (expr, STR); // static method, called directly
If (B)
System. Out. println (STR + "matches pattern" + expr );
Else
System. Out. println (STR + "does not match pattern" + expr );
}
}

 

However, expr in this example must be compiled each time before matching is performed, and the following example does not.

Import java. util. RegEx. pattern;
Import java. util. RegEx. matcher;

Public class regexdemo2 {
Public static void main (string Arg []) {
String expr;
String STR;

Expr = "P // WT"; // in Java, // indicates the backslash of the regular expression to be inserted, and the subsequent characters have special meanings. /W word characters
STR = "pot ";
Pattern pattern = pattern. Compile (expr );
Matcher = pattern. matcher (STR );
If (matcher. Matches ())
System. Out. println (STR + "matches pattern" + expr );
Else
System. Out. println (STR + "does not match pattern" + expr );
}
}

 

The pattern in the above example can be reused, for example:

Import java. util. RegEx. pattern;
Import java. util. RegEx. matcher;

Public class regexdemo3 {
Public static void main (string Arg []) {
String expr;

Expr = "P [aeiou] t ";
Pattern pattern = pattern. Compile (expr );
For (INT I = 0; I <Arg. length; I ++ ){
Matcher = pattern. matcher (ARG [I]);
If (matcher. Matches ())
System. Out. println (ARG [I] + "matches pattern" + expr );
Else
System. Out. println (ARG [I] + "does not match pattern" + expr );
}
}
}

 

Find the matched location in a paragraph:

Import java. util. RegEx. pattern;
Import java. util. RegEx. matcher;

Public class regexdemo4 {
Public static void main (string Arg []) {
String expr;
String STR;

Expr = "Bark ";
STR = "this is a larger block of text the pattern matcher" +
"Will search for the word bark. The pattern is very" +
"Simple. It will only match the word bark, and nothing" +
"Else. You can search a block of text for any of the" +
"Regular Expression Patterns -- not just bark .";
Pattern pattern = pattern. Compile (expr );
Matcher = pattern. matcher (STR );
Boolean found = matcher. Find ();
While (found ){
Int location = matcher. Start ();
System. Out. println (expr + "found at" + location );
Found = matcher. Find (location + 1 );
}
}
}
========================

Example:

Import java. util. RegEx. matcher;
Import java. util. RegEx. pattern;

/**
* Regular Expression example
*
* @ Author leizhimin 2009-7-17 9:02:53
*/
Public class testregx {
Public static void main (string [] ARGs ){
Pattern P = pattern. Compile ("F (. + ?) K ");
Matcher M = P. matcher ("fckfkkfkf ");
While (M. Find ()){
String S0 = M. Group ();
String S1 = M. Group (1 );
System. Out. println (S0 + "|" + S1 );
}
System. Out. println ("---------");
M. Reset ("fucking! ");
While (M. Find ()){
System. Out. println (M. Group ());
}

Pattern p1 = pattern. Compile ("F (. + ?) I (. + ?) H ");
Matcher M1 = p1.matcher ("finishabigfishfrish ");
While (m1.find ()){
String S0 = m1.group ();
String S1 = m1.group (1 );
String S2 = m1.group (2 );
System. Out. println (S0 + "|" + S1 + "|" + S2 );
}

System. Out. println ("---------");
Pattern P3 = pattern. compile ("(19 | 20) // D ([-/.]) (0 [1-9] | 1 [012]) // 2 (0 [1-9] | [12] [0-9] | 3 [01]) ");
Matcher m3 = p3.matcher ("1900-01-01 2007/08/13 19004251.01 1900 01 01 1900-01.01 1900 13 01 1900 02 31 ");
While (m3.find ()){
System. Out. println (m3.group ());
}
}
}

Output result: fck | C
Fkk | K
---------
Fuck
Finish | in | S
Fishfrish | ishfr | S
---------
1900-01-01
2007/08/13
190000001.01
1900 01 01
1900 02 31

Process finished with exit code 0

 

Author: gnuhpc
Source: http://www.cnblogs.com/gnuhpc/