Question

(java 1.5)

I have a need to build up a String, in pieces. I’m given a set of (sub)strings, each with a start and end point of where they belong in the final string. Was wondering if there were some canonical way of doing this. This isn’t homework, and I can use any licensable OSS, such as jakarta commons-lang StringUtils etc.

My company has a solution using a CharBuffer, and I’m content to leave it as is (and add some unit tests, of which there are none (?!)) but the code is fairly hideous and I would like something easier to read.

As I said this isn’t homework, and I don’t need a complete solution, just some pointers to libraries or java classes that might give me some insight. The String.Format didn’t seem QUITE right…

I would have to honor inputs too long and too short, etc. Substrings would be overlaid in the order they appear (in case of overlap).

As an example of input, I might have something like:

String:start:end

FO:0:3 (string shorter than field)

BAR:4:5 (String larger than field)

BLEH:5:9 (String overlays previous field)

I’d want to end up with

FO  BBLEH  
01234567890

(Edit: To all – StringBuilder (and specifically, the “pre-allocate to a known length, then use .replace()” theme) seems to be what I’m thinking of. Thanks to all who suggested it!)

Answer 1

StringBuilder output = new StringBuilder();
// for each input element
{
    while (output.length() < start)
    {
        output.append(' ');
    }
    output.replace(start, end, string);
}

You could also establish the final size of output before inserting any string into it. You could make a first pass through the input elements to find the largest end. This will be the final size of output.

char[] spaces = new char[size];
Arrays.fill(spaces, ' ');
output.append(spaces);