Question

How do I remove words from a text file that have symbols preceding them?

For example:

This is important information...  //but this is a comment
This is more important info...  //and this is another comment

How do I remove the words along with the symbol “//but this is a comment” ?

Here’s my pseudocode:

1. If "//" is detected, line.replace "//" symbol
2. Clear the words after the symbol 
3. Go on to the next line till you see "//" symbol
4. Repeat steps 1-3 (loop).

Note: this is occurring while the file is being read:

String line;
while ((line = textReader.readLine()) != null) 

Answer 1

I’m assuming that given:

This is important information...  //but this is a comment
This is more important info...  //and this is another comment

You want:

This is important information...
This is more important info...

Something like this should work:

Pattern pattern = Pattern.compile("//.*$", Pattern.DOTALL);
Matcher matcher = pattern.matcher(line);

line = matcher.replaceFirst("");

Pattern is what Java uses for regular expressions. Here’s some information about Java regular expressions in Java. The regex I’ve used looks for two forward slashes and everything after that until the end of the line. Then, the text that is matched is replaced by an empty string. Pattern.DOTALL tells Java to treat ^ and $ as beginning and end-of-line markers.

EDIT

This code below demonstrates how it works:

import java.util.regex.*; 

public class RemoveComments { 

   public static void main(String[] args){ 

      String[] lines = {"This is important information...  //but this is a comment", "This is more important info...  //and this is another comment"}; 
      Pattern pattern = Pattern.compile("//.*$", Pattern.DOTALL); 

      for(String line : lines) { 
          Matcher matcher = pattern.matcher(line); 

          System.out.println("Original: " + line); 
          line = matcher.replaceFirst(""); 

          System.out.println("New: " + line); 
      } 
   } 
}