regex - Error with comment detection using Regular Expression in java -

i have create simple code of comment detection.

import javax.swing.*; import java.util.regex.*; import java.awt.*; import java.awt.event.*; public class regex extends jframe implements actionlistener {     jpanel center=new jpanel();     jpanel title=new jpanel();     jtextarea text=new jtextarea();     jtextarea result=new jtextarea();     jscrollpane sctext=new jscrollpane(text);     jscrollpane scresult=new jscrollpane(result);     jbutton proc=new jbutton("proccess");     regex()     {         setsize(600,600);         setlayout(new borderlayout());         add(title,borderlayout.north);         title.setlayout(new gridlayout(1,2));         title.add(new jlabel("code"));         title.add(new jlabel("regex"));         add(center,borderlayout.center);         center.setlayout(new gridlayout(1,2));         center.add(sctext);         center.add(scresult);         add(proc,borderlayout.south);         proc.addactionlistener(this);         show();     }     public void actionperformed(actionevent e)     {         if(e.getsource()==proc)         {             try             {                 result.settext("");                 matcher m=pattern.compile("(/\\*(.|[\\n]|(\\*+([^*/]|[\\r\\n])))*\\*+/)|(//.*)").matcher(text.gettext());                 while(m.find())                 {                     result.append(m.group()+"\n");                 }             }             catch(exception x)             {                 try                 {                     file err = new file("error.txt");                     java.io.printstream ps = new java.io.printstream(err);                     x.printstacktrace(ps);                     ps.close();                 }                 catch(exception exx){}             }         }     }     public static void main(string[]agrs)     {         new regex();     } } 

i don't know why code can't detect long comments.
i have sample of text contain long comment.

/*  * apache software license, version 1.1  *  * copyright (c) 1999-2003 apache software foundation.  rights   * reserved.  *  * redistribution , use in source , binary forms, or without  * modification, permitted provided following conditions  * met:  *  * 1. redistributions of source code must retain above copyright  *    notice, list of conditions , following disclaimer.   *  * 2. redistributions in binary form must reproduce above copyright  *    notice, list of conditions , following disclaimer in  *    documentation and/or other materials provided  *    distribution.  *  * 3. end-user documentation included redistribution, if  *    any, must include following acknowlegement:    *       "this product includes software developed   *        apache software foundation (http://www.apache.org/)."  *    alternately, acknowlegement may appear in software itself,  *    if , wherever such third-party acknowlegements appear.  *  * 4. names "the jakarta project", "tomcat", , "apache software  *    foundation" must not used endorse or promote products derived  *    software without prior written permission. written   *    permission, please contact apache@apache.org.  *  * 5. products derived software may not called "apache"  *    nor may "apache" appear in names without prior written  *    permission of apache group.  *  * software provided ``as is'' , expressed or implied  * warranties, including, not limited to, implied warranties  * of merchantability , fitness particular purpose  * disclaimed.  in no event shall apache software foundation or  * contributors liable direct, indirect, incidental,  * special, exemplary, or consequential damages (including, not  * limited to, procurement of substitute goods or services; loss of  * use, data, or profits; or business interruption) caused ,  * on theory of liability, whether in contract, strict liability,  * or tort (including negligence or otherwise) arising in way out  * of use of software, if advised of possibility of  * such damage.  * ====================================================================  *  * software consists of voluntary contributions made many  * individuals on behalf of apache software foundation.  more  * information on apache software foundation, please see  * <http://www.apache.org/>.  *  */  

but it's working in detecting short comment.

program catch lot of error

it seems java regular expression engine recursion-based. means regular expression has optimized produce fewer backtrackings. yet cannot see backtracking produces call stack.

following proposals work larger comments:

• pattern.compile("(/\\*.*?\\*/)", pattern.dotall) (matches /* .. */)
• pattern.compile("(/\\*([^\\*]|(\\*(?!/))+)*+\\*+/)|(//.*)")

explanation:

• (.| ...)* produces backtrackings because . matches (almost) character , other alternatives matching .* - first action eliminate .. in case replace [^\\*].
• [^\\*]|[\\n] == [^\\*] remove [\\n]
• [^*/]|[\\r\\n] == [^*/] remove [\\r\\n]
• to prevent backtracking use *+ after content loop (possessive regular expression). requires last dot not consumed content loop. insert negative loopahead / after matched *, i.e. (\\*(?!/))+