print only the single and multiple line comments when reading a java sample code

[Mohammad Ali Raisi]

with this program i want to print only the comments messages but it does not work it is also possible that i check with indexof but i dont know how to use any body help please

public static void main(String[] args) {
        String line;
        try {
            BufferedReader br=new BufferedReader(new FileReader("E:\\Sum.txt"));
                while((line=br.readLine())!=null)
                {
                    if(line.startsWith("//"))
                        
                        
                    if(line.startsWith("/*"))
                    {
                      
                        while(!(line=br.readLine()).endsWith("'*\'"))
                        {
                           
                        break;
                        
                        } 
                    }
                    System.out.println(line);
          
                }
                br.close();
        }
             catch (IOException e) {
                e.printStackTrace();
            }

        
        } 

[Dave Tolls]

What is the issue with the current code?
What is it not doing?

One thing that does come to mind.  What if there is white space before the '//' or '/*'?
Or  anything, for that matter?

[John Joe]

Please wrap your code using code tags next time.

[Junilu Lacar]

Block comments end with "*/", your program checks for *\ instead.

[Carey Brown]

You really need to clean up the indentation. Your current indentation is hiding some fundamental flaws. I would also insist that you include braces after  each and every if(), else, while, for, etc.. Without them the code is not doing what you expect. Post your cleaned up version back here.

What happens when you have two if's back to back as you do on lines 7 and 10?

[Mohammad Ali Raisi]

please check this one it will read the attached file, the indentation is print only the comments when reading Sum.txt

public class BufferedReaderExample {   

    public static void main(String args[]) throws IOException{
      
        //reading file line by line in Java using BufferedReader       
        FileInputStream fis = null;
        BufferedReader br = null;
        //String line;
        try {
            fis = new FileInputStream("E:/Sum.txt");
            br = new BufferedReader(new InputStreamReader(fis));
            String line;
            while((line = br.readLine()) != null){
                if (line.contains("//"))
                     System.out.println(line.substring(0, line.indexOf("\\")));
                if (line.contains("/*")) {
                       System.out.println(line.substring(line.indexOf("/*")));
                       while ((line = br.readLine()) != null || !line.contains("*/")) {
                             System.out.println(line);
                             
                        }              
                       if (line.contains("*/")) {
                                System.out.println(line.substring(0, line.indexOf("*/")));
                                      
                    }
            }
                
            }
            br.close();
          
            
  }
        catch(IOException e){
            System.out.println("file could not read");
            
        }
        catch(NullPointerException e) {
        System.out.println("file is empty");
}
        
    }
   
}

BUILD SUCCESSFUL (total time: 1 second)
but I need like print only singl line and multiple line comments like bellow

this is the first program

sum of the number

the total number going to sum

count ++

it is the result

[Carey Brown]

Here you have forward slashes (correct) in one place and backwards slashes in the other.

                if (line.contains("//"))
                     System.out.println(line.substring(0, line.indexOf("\\")));

[Carey Brown]

You are not handling the case where the comment is all on one line.

int a = 42; /* some comment */

Do you have a sample file that you are running through your program, and does that file have all the possible comment variations that you can come up with?

[Carey Brown]

while( ( line = br.readLine() ) != null || !line.contains( "*/" ) )

WHILE line is not equal to null OR line does NOT contain "*/"
Notice that it can't get to the OR expression unless line IS null, in which case you'll get a null pointer exception.

[Carey Brown]

Your indentation is better but could be even better than that.

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class BufferedReaderExample
{
	public static void main( String args[] ) throws IOException
	{
		// reading file line by line in Java using BufferedReader
		FileInputStream fis = null;
		BufferedReader br = null;
		// String line;
		try {
			fis = new FileInputStream( "E:/Sum.txt" );
			br = new BufferedReader( new InputStreamReader( fis ) );
			String line;
			while( ( line = br.readLine() ) != null ) {
				if( line.contains( "//" ) )
					System.out.println( line.substring( 0, line.indexOf( "\\" ) ) );
				
				if( line.contains( "/*" ) ) {
					System.out.println( line.substring( line.indexOf( "/*" ) ) );
					
					while( ( line = br.readLine() ) != null || ! line.contains( "*/" ) ) {
						System.out.println( line );
					}
					
					if( line.contains( "*/" ) ) {
						System.out.println( line.substring( 0, line.indexOf( "*/" ) ) );
					}
				}
			}
			br.close();
		}
		catch( IOException e ) {
			System.out.println( "file could not read" );
		}
		catch( NullPointerException e ) {
			System.out.println( "file is empty" );
		}
	}
}

[Carey Brown]

Carey Brown wrote:Here you have forward slashes (correct) in one place and backwards slashes in the other.

                if (line.contains("//"))
                     System.out.println(line.substring(0, line.indexOf("\\")));

Also, your substring will be all characters up to "\\" instead of after. Note that "\\" should have been "//".

[Carey Brown]

                if( line.contains( "//" ) )
                    System.out.println( line.substring( 0, line.indexOf( "\\" ) ) );
                 
                if( line.contains( "/*" ) ) {
                    System.out.println( line.substring( line.indexOf( "/*" ) ) );

Second if should have been an else-if. What do you expect to happen for this comment:

int a = 42; // some text /* even more text

What about this case:

int a = 42; /* some text // more text */

[Mohammad Ali Raisi]

thank you for the reply, yes you are right is forward slash "//" and actually I did not expect those condition now it will be better to consider those conditions as well, and i attached the sample file that I am using please have it and help me to solve the issue because tomorrow i have to submit my homework

[Paul Clapham]

There are more conditions which you haven't considered. Like for example a line of code which you posted here:

if( line.contains( "/*" ) ) {

That /* doesn't start a comment because it's inside a string literal.

[Mohammad Ali Raisi]

Dear Mr. Sheriff, as my program knowledge is not that much good and I could not applied those conditions, could you please help for few that how do I apply, thank you

[Carey Brown]

Mohammad Ali Raisi wrote:thank you for the reply, yes you are right is forward slash "//" and actually I did not expect those condition now it will be better to consider those conditions as well, and i attached the sample file that I am using please have it and help me to solve the issue because tomorrow i have to submit my homework

I don't see the example file attachment anywhere. Could you re-post it?

Extracting all Java comments in every use case is a non-trivial undertaking. I would assume for the moment that all that is needed to meet the requirements is to be able to parse the example file.

[Mohammad Ali Raisi]

thank you the bellow code is he sample file could, I already attached but no problem, please save it in a txt file and do the operation.

package javaapplication5;

/**
*
* @author MOHAMMADALI
*/
public class Sum {
   
   
   
   
 public static void main(String[] args){
   

     
     int sum=0;
      /*
        this is the first program
      */
     //sum of the number
     int n = 10;// the total number going to sum
     int count = 0;
     //loop to sum all number
     for(int i=0; i<n;i++)
     {
         //count ++;
         sum= sum+ i;
     }
     System.out.println("the sum of the numbers are ="+ sum);
     //it is the result
     // this is /* a test1
     /* this is a test // program */
     
 }
   
}

[Mohammad Ali Raisi]

one way is doing by indexof that search character by character and then print the needed part but i could not do.

[Mark Spencers]

You can use regex for this . The following regex escapes * to match it literally and uses group () to print only contennt between block comments.

public static void main(String[] args) {
		String s = "public void /* sdksd\n\nksssd\nsd */ main class";
		Matcher matcher = Pattern.compile("/\\*([^*/]*)\\*/").matcher(s);
		while (matcher.find()) {
			String group = matcher.group(1);
			System.out.println(group);
		}
	}

Prints:

 sdksd

ksssd
sd 

[Mohammad Ali Raisi]

thank you, I think this is not a good solution because it makes program static, that we could not put all comments one by one may be we have many comments it dynamically must understand those and print please help for the previous code that i wrote

[Carey Brown]

You've undoubtedly made some changes since the last post of your code. Could you re-post the current version of your code so that we may comment on that?

[Mohammad Ali Raisi]

this is a very nice program but it remove the comments and print other content of txt file so please tell me where i have to change that it prints comments and remove the other contents.

public class CodeCleaner
{
       public void removeComments( String fileName )
      {
            int ch;
            boolean slashCommentFound = false;
            boolean starCommentFound = false;
            boolean firstSlashFound = false;
            boolean startOfComment = false;
            boolean endOfComment = false;
            boolean startDoubleQuoteFound = false;
           StringBuilder javaDoc = new StringBuilder();
  
           try
          {
                     BufferedReader reader =
                                        new BufferedReader( new FileReader( fileName ) );
   
                      while( ( ch = reader.read() ) != -1 )
                     {
                             javaDoc.append( (char)ch );
    
                             if( ch == '\"' )
                                      startDoubleQuoteFound = !startDoubleQuoteFound;
    
                             if( startDoubleQuoteFound
                                  && ( starCommentFound == true
                                  || slashCommentFound == true ) )
                                       continue;
    
                              if( ch == '/' )
                             {
                                    if( starCommentFound == true
                                                  && endOfComment == false )
                                              continue;
     
                                      if( endOfComment
                                                 && starCommentFound == true )
                                      {
                                             starCommentFound = false;
                                             endOfComment = false;
                                             startOfComment = false;
                                             continue;
                                       }

                                     else if( firstSlashFound
                                                   && slashCommentFound == false
                                                   && starCommentFound == false )
                                     {
                                               slashCommentFound = true;
                                               firstSlashFound = false;
                                               continue;
                                     }

                                     else if( slashCommentFound == false
                                                   && starCommentFound == false
                                                   && startDoubleQuoteFound == false )
                                   {
                                          firstSlashFound = true;
                                          continue;
                                   }
                   }
    
                  if( ch == '*' )
                 {
                          if( starCommentFound )
                          {
                                 endOfComment = true;
                                 continue;
                          }

                           if( firstSlashFound
                                              && starCommentFound == false )
                          {
                                   starCommentFound = true;
                                   firstSlashFound = false;
                                   continue;
                           }

                          else if( startOfComment == false
                                             && starCommentFound == true )
                           {
                                       startOfComment = true;
                                       continue;
                          }
               }

               if( ch == '\n' )
             {
                      if( slashCommentFound )
                      {
                             slashCommentFound = false;
                             startOfComment = false;
                             firstSlashFound = false;
                             starCommentFound = false;
                             System.out.print( ( char ) ch );
                             continue;
                        }
               }
    
               if( starCommentFound == true
                         && endOfComment == false )
                         continue;
    
                String doc = javaDoc.toString();
    
                 if(doc.trim().startsWith( "/**" ) && doc.trim().endsWith( "*/" ))
               {
                           System.out.print(javaDoc.toString());
                           javaDoc = new StringBuilder();
               }
    
               if( ch != '/' && ch != '*' )
               {
                         if( endOfComment )
                                System.out.print( ( char ) ch );
     
                         endOfComment = false;
                         firstSlashFound = false;
                         startOfComment = false;
                         endOfComment = false;
               }

                 if( slashCommentFound == false
                        && starCommentFound == false )
                 {
                           javaDoc = new StringBuilder();
                           System.out.print( ( char ) ch );
                 }
      }

       reader.close();

       }
      catch( FileNotFoundException ex )
      {
              System.out.println( fileName + " not found" );
       }
      catch( Exception ex )
      {
               System.out.println( "Error reading file " + fileName );
               ex.printStackTrace();
       }
 }

   public static void main( String[] args )
 {
       CodeCleaner reader = new CodeCleaner();
       reader.removeComments( "E:/Sum.txt" );
 }
}

Output

public class Sum {
   
   
   
   
 public static void main(String[] args){
   

     
     int sum=0;
     
     
     System.out.println("please enter the number");
     int n = 10;
     int count = 0;
     
     for(int i=0; i<n;i++)
     {
         
         sum= sum+ i;
     }
     System.out.println("the sum of the numbers are ="+ sum);
     
     
     
     
 }
   
}BUILD SUCCESSFUL (total time: 0 seconds)

but i want the output like bellow

this is the first program

count ++

it is the result

[Mohammad Ali Raisi]

this is the content of file which i read in the above program

public class Sum {
   
   
   
   
 public static void main(String[] args){
   

     
     int sum=0;
      /*
        this is the first program
      */
     //sum of the number
     System.out.println("please enter the number");
     int n = 10;// the total number going to sum
     int count = 0;
     //loop to sum all number
     for(int i=0; i<n;i++)
     {
         //count ++;
         sum= sum+ i;
     }
     System.out.println("the sum of the numbers are ="+ sum);
     //it is the result
     
     
 }
   
}

[Carey Brown]

Trying to turn a program that does one thing (i.e. remove comments) is not a good way to come up with a program to serve the opposite purpose (i.e. extract comments).

The problem is tricky. You need to detect three states: string constant, slash-slash comment, and slash-star comment. You could read the file line-by-line but as you found out it takes a little thought to handle slash-start comments that may bridge multiple lines or may have multiple occurrences on a single line. So, you could instead go character-by-character but this would involve setting one or more flags to determine what state you're in.

Another approach would be to load the entire file into a StringBuilder and then have a 'pos' variable that you increment through the string using charAt(). What this gives you is an easy way to look ahead  one character. As an example:

if( sbin.charAt( pos ) == '/' && sbin.charAt( pos + 1 ) == '*' ) // where 'sbin' is StringBuilder input, ie the whole file

It also greatly simplifies things by allowing you to create three separate parse methods that are independent of each other.

public class CopyOfJavaCommentExtractor
{
	public static void main( String[] args ) throws IOException
	{
		StringBuilder	sbin = new StringBuilder();
		
		// Read in the entire file
		try( BufferedReader in = new BufferedReader(
				new InputStreamReader( new FileInputStream( "testcomment.txt" ) ) ) )
		{
			String		line;
			while( (line = in.readLine()) != null )
				sbin.append( line ).append( '\n' );
		}
		
		int				pos = 0;

		while( pos < sbin.length() )
		{
			if( sbin.charAt( pos ) == '"' )
				pos = parseString( sbin, pos );
			else if( sbin.charAt( pos ) == '/' && sbin.charAt( pos + 1 ) == '*' )
				pos = parseStarComment( sbin, pos );
			else if( sbin.charAt( pos ) == '/' && sbin.charAt( pos + 1 ) == '/' )
				pos = parseSlashComment( sbin, pos );
			else
				pos++;
		}
	}
	
	// Example:
	private static int parseString( StringBuilder sbin, int pos )
	{
		// returns the new position after string has been parsed
	}

    // the other two parsers would print out the parsed text
}

[Mohammad Ali Raisi]

thank you for the help I could not get your code, could you please put the complete code as i told i don't have programming background but I try my best to learn

[Carey Brown]

Is this a homework assignment?

[Mohammad Ali Raisi]

yes it is my friend

[Carey Brown]

We don't like to do peoples' homework here. We will give helpful hints and answer specific questions, and occasionally provide snipits of code. It sounds like your instructor may not have given you enough background to complete this assignment. If you have any specific questions, ask away.

[Mohammad Ali Raisi]

that is specific question that i wrote a program asked you for help but you suggest me another one that i did not understand your code i asked for complete one it is not suppose to submit that one because my homework is parser not this but it is part of that i did with above code and it had error i asked you to please resolve the error

[Carey Brown]

The code you posted yesterday a 9:49am can be made to handle some of the comments if you limit the scope to:

// comment on one line
/*
comment
*/ on multiple lines

And forget about:

/* comment */
/* comment1 */ code /* comment2 */
/* comment // more
*/

I've already mentioned some correction that you need to make.
Line 16: needs to be else-if
Line 15: Needs substring of line AFTER "//".
Line 15: Change "\\"
Line 18: You boolean expression needs to be fixed

[Mohammad Ali Raisi]

thank you, do you think in real code we have those kinds of comments that you mentioned?

[Carey Brown]

They are rarer but they do occur. Unfortunately handling those cases means that your code would need a redesign so as to read character by character instead of by line. This gets quite a bit messier and I would point you back to my post today at 10:46am

[Paul Clapham]

Carey Brown wrote:Extracting all Java comments in every use case is a non-trivial undertaking.

We haven't talked about Unicode escapes, either. It's extremely unlikely that you would find a Java program where the // starting a comment had been Unicode-escaped, but nevertheless it's part of the Java specification and it's the sort of thing that some instructors would be sure to use as a test case.

[Carey Brown]

If you're interested, this is my test file from when I developed a similar utility.

testcomment.txt
Some of these are rarer than others but all have been seen in
production code.

// slash slash comment
 // space slash slash
int a = 42; // code slash slash
// slash slash /* slash star
// slash slash /* slash star star slash */
// slash slash // slash slash
//slash slash no leading space
//// slash slash slash slash
//
/* slash star one line comment */
/*slash star one line comment no leaading space */
/* slash star
 * multi-line
 * star slash
 */
/*
 * slash star
 * multi-line 2
 * star slash
 */
/* slash star
 * multi-line 3
 * star slash */
/*  //  slash star slash slash - star slash */
/* /* slash star slash star - star slash */
/*
multi-line 4 without leading star
*/
/*** slash star star star - star slash */
/*** slash star star star - star star star slash ***/
/**/  (empty)
 "String with /* slash star - star slash EOS"
String s = "string /* with \" escaped double quote /*";
/** javadoc */
/**
 * Another javadoc comment
 * @param xyz will be some parameter
 * @return some value
 */
 

[Carey Brown]

This thread has been quite for 4 days so I'm going to assume that the issue is closed and that it would be safe to post the answer from some code I have.

package csb;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;

public class JavaCommentExtractor
{
	public static void main( String[] args ) throws IOException
	{
		if( args.length == 0 )
			extractComments( "testcomment.txt" );
		else
			extractComments( args );
	}
	
	private static void extractComments( String... fnames )
	{
		for( String fname : fnames )
		{
			StringBuilder	sbin = new StringBuilder();
			
			System.out.println( "=============================================== " + fname );
			// Read in the entire file
			// Try-with-resources requires Java-7+
			try( BufferedReader in = new BufferedReader(
					new InputStreamReader( new FileInputStream( fname ) ) ) )
			{
				String		line;
				while( (line = in.readLine()) != null )
					sbin.append( line ).append( '\n' );
			}
			catch( IOException e )
			{
				e.printStackTrace();
			}
			String		wholeFile = sbin.toString();

			for( int pos=0 ; pos < wholeFile.length() ; )
			{
				if( wholeFile.charAt( pos ) == '"' )
					pos = parseString( wholeFile, pos+1 );
				else if( wholeFile.charAt( pos ) == '\'' )
					pos = parseCharacter( wholeFile, pos+1 );
				else if( wholeFile.charAt( pos ) == '/' )
				{
					if( eq( wholeFile, pos, "/**" ) && ws( wholeFile.charAt( pos + 3  ) ) )
						pos = parseJavadocComment( wholeFile, pos+4 );
					else if( eq( wholeFile, pos, "/**/" ) )
						pos += 4; // empty comment - no print
					else if( eq( wholeFile, pos, "/*" ) )
						pos = parseStarComment( wholeFile, pos+2 );
					else if( eq( wholeFile, pos, "//" )  )
						pos = parseSlashComment( wholeFile, pos+2 );
					else
						pos++;
				}
				else
					pos++;
			}
		}
	}
	
	// test for match equals current position in String
	private static boolean eq( String sb, int pos, String match )
	{
		if( pos + match.length() > sb.length() )
			return false;
		for( int i=0 ; i < match.length() ; i++ )
			if( sb.charAt(pos+i) != match.charAt( i ) )
				return false;
		return true;
	}
	
	// test for white space
	private static boolean ws( char c )
	{
		return c == ' ' || c == '\t' || c == '\n' || c == '\r';
	}
	
	private static int parseCharacter( String wholeFile, int pos )
	{
		StringBuilder		sb = new StringBuilder();
		while( wholeFile.charAt( pos ) != '\'' )
		{
			sb.append( wholeFile.charAt( pos ) );
			if( wholeFile.charAt( pos ) == '\\' )
			{
				pos++; // skip escaped character
				sb.append( wholeFile.charAt( pos ) );
			}
			pos++;
		}
//		print( "CHAR", sb.toString() );
		//  no print
		return pos + 1;
	}
	
	private static int parseString( String wholeFile, int pos )
	{
		StringBuilder		sb = new StringBuilder();
		while( wholeFile.charAt( pos ) != '"' )
		{
			sb.append( wholeFile.charAt( pos ) );
			if( wholeFile.charAt( pos ) == '\\' )
			{
				pos++; // skip escaped character
				sb.append( wholeFile.charAt( pos ) );
			}
			pos++;
		}
//		print( "STRING", sb.toString() );
		//  no print
		return pos + 1;
	}
	
	private static int parseJavadocComment( String wholeFile, int pos )
	{
		StringBuilder		sb = new StringBuilder();
		for( ; ! eq( wholeFile, pos, "*/" ) ; pos++ )
			sb.append( wholeFile.charAt(pos) );
		print( "/**", sb.toString() );
		return pos + 2;
	}
	
	private static int parseStarComment( String wholeFile, int pos )
	{
		StringBuilder		sb = new StringBuilder();
		for( ; ! eq( wholeFile, pos, "*/" ) ; pos++ )
			sb.append( wholeFile.charAt(pos) );
		print( "/*", sb.toString() );
		return pos + 2;
	}
	
	private static int parseSlashComment( String wholeFile, int pos )
	{
		StringBuilder		sb = new StringBuilder();
		for( ; wholeFile.charAt(pos) != '\n' ; pos++ )
			sb.append( wholeFile.charAt(pos) );
		print( "//", sb.toString() );
		return pos + 1;
	}
	
	// print with msg prefix. this is for debugging purposes
	// could be modified to strip off leading '*' on multi-line
	// comments
	private static void print( String msg, String sb )
	{
		String s = sb.toString().trim();
		if( s.length() > 0 ) // don't bother with empty comments
			System.out.println( s + "\r\n" );
	}
}

[Mohammad Ali Raisi]

Dear Friends,
thank you for such a great help it works very well

[Mohammad Ali Raisi]

thank you Mr. Carey Brown I have learned many things from your code

[Carey Brown]

Mohammad Ali Raisi wrote:thank you Mr. Carey Brown I have learned many things from your code

You're welcome.

I hope I didn't post the answer too soon.

You can see how there's many subtleties to this problem.