Putting char into a java string for each N characters

I have a java string, which has a variable length.

I need to put the piece "<br>" into the string, say each 10 characters.

For example this is my string:

`this is my string which I need to modify...I love stackoverlow:)`

How can I obtain this string?:

`this is my<br> string wh<br>ich I nee<br>d to modif<br>y...I love<br> stackover<br>flow:)`

Thanks

Solution 1:

Try:

String s = // long string
s.replaceAll("(.{10})", "$1<br>");

EDIT: The above works... most of the time. I've been playing around with it and came across a problem: since it constructs a default Pattern internally it halts on newlines. to get around this you have to write it differently.

public static String insert(String text, String insert, int period) {
    Pattern p = Pattern.compile("(.{" + period + "})", Pattern.DOTALL);
    Matcher m = p.matcher(text);
    return m.replaceAll("$1" + insert);
}

and the astute reader will pick up on another problem: you have to escape regex special characters (like "$1") in the replacement text or you'll get unpredictable results.

I also got curious and benchmarked this version against Jon's above. This one is slower by an order of magnitude (1000 replacements on a 60k file took 4.5 seconds with this, 400ms with his). Of the 4.5 seconds, only about 0.7 seconds was actually constructing the Pattern. Most of it was on the matching/replacement so it doesn't even ledn itself to that kind of optimization.

I normally prefer the less wordy solutions to things. After all, more code = more potential bugs. But in this case I must concede that Jon's version--which is really the naive implementation (I mean that in a good way)--is significantly better.

Solution 2:

Something like:

public static String insertPeriodically(
    String text, String insert, int period)
{
    StringBuilder builder = new StringBuilder(
         text.length() + insert.length() * (text.length()/period)+1);

    int index = 0;
    String prefix = "";
    while (index < text.length())
    {
        // Don't put the insert in the very first iteration.
        // This is easier than appending it *after* each substring
        builder.append(prefix);
        prefix = insert;
        builder.append(text.substring(index, 
            Math.min(index + period, text.length())));
        index += period;
    }
    return builder.toString();
}

Solution 3:

You can use the regular expression '..' to match each two characters and replace it with "$0 " to add the space:

s = s.replaceAll("..", "$0 "); You may also want to trim the result to remove the extra space at the end.

Alternatively you can add a negative lookahead assertion to avoid adding the space at the end of the string:

s = s.replaceAll("..(?!$)", "$0 ");

For example:

String s = "23423412342134"; s = s.replaceAll("....", "$0<br>"); System.out.println(s);

Output: 2342<br>3412<br>3421<br>34