Java Tutorial/Regular Expressions/Pattern

A simple pattern matching demo.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr {

 public static void main(String args[]) {
   Pattern pat;
   Matcher mat;
   boolean found;
   pat = Pattern.rupile("Java");
   mat = pat.matcher("Java");
   found = mat.matches(); 
   if (found)
     System.out.println("Matches");
   else
     System.out.println("No Match");
   mat = pat.matcher("Java 2"); 
   found = mat.matches(); 
   if (found)
     System.out.println("Matches");
   else
     System.out.println("No Match");
 }

}</source>

Control the pattern case

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class MainClass {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("java", Pattern.CASE_INSENSITIVE);
   String candidateString = "Java. java JAVA jAVA";
   Matcher matcher = p.matcher(candidateString);
   // display the latter match
   System.out.println(candidateString);
   matcher.find(11);
   System.out.println(matcher.group());
   // display the earlier match
   System.out.println(candidateString);
   matcher.find(0);
   System.out.println(matcher.group());
 }

} /*

• /</source>

Java. java JAVA jAVA
JAVA
Java. java JAVA jAVA
Java

Pattern.compile method

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class MainClass {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("\\d");
   Matcher matcher = p.matcher("5");
   boolean isOk = matcher.matches();
   System.out.println("original pattern matches " + isOk);
   // recycle the pattern
   String tmp = p.pattern();
   Pattern p2 = Pattern.rupile(tmp);
   matcher = p.matcher("5");
   isOk = matcher.matches();
   System.out.println("second pattern matches " + isOk);
 }

}</source>

Reuse Pattern Method

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class MainClass {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("\\d");
   Matcher matcher = p.matcher("5");
   boolean isOk = matcher.matches();
   System.out.println("original pattern matches " + isOk);
   // recycle the pattern
   String tmp = p.pattern();
   Pattern p2 = Pattern.rupile(tmp);
   matcher = p.matcher("5");
   isOk = matcher.matches();
   System.out.println("second pattern matches " + isOk);
 }

}</source>

Split by :

   <source lang="java">

/*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*
*   - Neither the name of Sun Microsystems nor the names of its
*     contributors may be used to endorse or promote products derived
*     from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.util.regex.Pattern; public class SplitDemo {

 private static final String REGEX = ":";
 private static final String INPUT = "one:two:three:four:five";
 public static void main(String[] args) {
   Pattern p = Pattern.rupile(REGEX);
   String[] items = p.split(INPUT);
   for (String s : items) {
     System.out.println(s);
   }
 }

}</source>

Split by number

   <source lang="java">

/*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*
*   - Neither the name of Sun Microsystems nor the names of its
*     contributors may be used to endorse or promote products derived
*     from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.util.regex.Pattern; public class SplitDemo2 {

 private static final String REGEX = "\\d";
 private static final String INPUT = "one9two4three7four1five";
 public static void main(String[] args) {
   Pattern p = Pattern.rupile(REGEX);
   String[] items = p.split(INPUT);
   for (String s : items) {
     System.out.println(s);
   }
 }

}</source>

Use a character class.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr7 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("[a-z]+");
   Matcher mat = pat.matcher("this is a test.");
   while (mat.find())
     System.out.println("Match: " + mat.group());
 }

}</source>

Use a quantifier.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr4 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("W+");
   Matcher mat = pat.matcher("W WW WWW");
   while (mat.find())
     System.out.println("Match: " + mat.group());
 }

}</source>

Use find() to find a subsequence.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr2 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("Java");
   Matcher mat = pat.matcher("Java 2");
   System.out.println("Looking for Java in Java 2.");
   if (mat.find())
     System.out.println("subsequence found");
   else
     System.out.println("No Match");
 }

}</source>

Use find() to find multiple subsequences.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr3 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("test");
   Matcher mat = pat.matcher("test 1 2 3 test");
   while (mat.find()) {
     System.out.println("test found at index " + mat.start());
   }
 }

}</source>

Use Pattern class to match

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class MainClass {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("B(on)d");
   String candidateString = "My name is Bond. James Bond.";
   String matchHelper[] = { "               ^", "              ^", "                           ^",
       "                          ^" };
   Matcher matcher = p.matcher(candidateString);
   // find the end point of the second sub group (ond)
   int nextIndex = matcher.end(1);
   System.out.println(candidateString);
   System.out.println(matchHelper[3] + nextIndex);
 }

}</source>

Use the ? quantifier.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr6 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("e.+?d");
   Matcher mat = pat.matcher("extend cup end table");
   while (mat.find())
     System.out.println("Match: " + mat.group());
 }

}</source>

Use wildcard and quantifier.

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; class RegExpr5 {

 public static void main(String args[]) {
   Pattern pat = Pattern.rupile("e.+d");
   Matcher mat = pat.matcher("extend cup end table");
   while (mat.find())
     System.out.println("Match: " + mat.group());
 }

}</source>