Java regex search. ".*" macther.find() or matcher.replaceAll, give more matches than intended

[George Cui]

// Java regex question. Execute the following:
  public static void  main (String [] args) {

      // Replace a matched regex results in a SB with a specific string
       String s1 = "This 1 is line one";
       String s2 = "This 2 is line two";
       String s3 = "This 3 is line three";
       String s4 = "This 4 is line Four";
       StringBuffer sb = new StringBuffer ();
       sb = sb.append(s1).append(System.getProperty("line.separator"))
   			.append(s2).append(System.getProperty("line.separator"))
   			.append(s3).append(System.getProperty("line.separator"))
   			.append(s4);
       System.out.println(sb);
       Pattern p = Pattern.compile(".*", Pattern.MULTILINE);// multiple line or not ,same    
                                                 // if "^.*$" , the result is the same                        
       Matcher m = p.matcher(sb);
       int cnt =0;
       while (m.find()) {
         cnt++;
         String num = m.group();
         System.out.println(cnt+" "+num);
         
       }
       String s =m.replaceAll("XXX");
       System.out.println("ReplaceAll:\n"+s);
       s =m.replaceFirst("XxX");
       System.out.println("replace first :"+s);
       
    
  }

I got results:
This 1 is line one
This 2 is line two
This 3 is line three
This 4 is line Four
1 This 1 is line one
2
3
4 This 2 is line two
5
6
7 This 3 is line three
8
9
10 This 4 is line Four
11
ReplaceAll:
XXXXXX
XXX
XXXXXX
XXX
XXXXXX
XXX
XXXXXX
replace first :XxX
This 2 is line two
This 3 is line three
This 4 is line Four

That means if I use ".*", a single line will have 2 matches (try just one line case ) and another find is the line.separator. If I pass that, it will replace lines that I do not intended to replace. I just want
XXX
XXX
XXX
XXX

If the search pattern flawed or I should do something in the code to skip the 2 additional XXX (which I prefer not to do any manipulation to change the meaning of the search)

[Rob Spoor]

Add Pattern.DOTALL to your flags: Pattern.MULTILINE | Pattern.DOTALL. Without it, . does not match the line breaks. Pattern.MULTILINE only changes the treatment of ^ and $.

[George Cui]

Thanks for all the quick reponses. Sorry that it was my very first post and did not know how to format it in the page.
I tried to use
Pattern.MULTILINE | Pattern.DOTALL, it gives me this

This 1 is line one
This 2 is line two
This 3 is line three
This 4 is line Four
1 This 1 is line one
This 2 is line two
This 3 is line three
This 4 is line Four
2
ReplaceAll:
XXXXXX
replace first :XxX

It treat the whole StringBuffer as one big line (with 2 matches in 2 replacements resulting in XXXXXX), I want to search such that replaveAll will get me
XXX
XXX
XXX
instead of XXXXXX
Is my search pattern wrong or is something else is not used properly
Thanks -George

[Rob Spoor]

So you want to replace everything but the line breaks with XXX? Then don't use . but explicitly say "everything but line breaks": [^\r\n].

[George Cui]

Thanks so much Rob. It works with ".*[^\r\n]"
What a great site for asking for help!

[Rob Spoor]

You're welcome.