How to trim a java stringbuilder?

Question

I have a StringBuilder object that needs to be trimmed (i.e. all whitespace chars /u0020 and below removed from either end).

I can\'t seem to find a method in string

Answer 1

I've used Zaven's analysis approach and StringBuilder's delete(start, end) method which performs far better than the deleteCharAt(index) approach, but slightly worse than the substring() approach. This method also uses the array copy, but array copy is called far fewer times (only twice in the worst case). In addition, this avoids creating multiple instances of intermediate Strings in case trim() is called repeatedly on the same StringBuilder object.

public class Main {

    public static String trimOriginal(StringBuilder sb) {
        return sb.toString().trim();
    }

    public static String trimDeleteRange(StringBuilder sb) {
        int first, last;

        for (first = 0; first < sb.length(); first++)
            if (!Character.isWhitespace(sb.charAt(first)))
                break;

        for (last = sb.length(); last > first; last--)
            if (!Character.isWhitespace(sb.charAt(last - 1)))
                break;

        if (first == last) {
            sb.delete(0, sb.length());
        } else {
           if (last < sb.length()) {
              sb.delete(last, sb.length());
           }
           if (first > 0) {
              sb.delete(0, first);
           }
        }
        return sb.toString();
    }


    public static String trimSubstring(StringBuilder sb) {
        int first, last;

        for (first = 0; first < sb.length(); first++)
            if (!Character.isWhitespace(sb.charAt(first)))
                break;

        for (last = sb.length(); last > first; last--)
            if (!Character.isWhitespace(sb.charAt(last - 1)))
                break;

        return sb.substring(first, last);
    }

    public static void main(String[] args) {
        runAnalysis(1000);
        runAnalysis(10000);
        runAnalysis(100000);
        runAnalysis(200000);
        runAnalysis(500000);
        runAnalysis(1000000);
    }

    private static void runAnalysis(int stringLength) {
        System.out.println("Main:runAnalysis(string-length=" + stringLength + ")");

        long originalTime = 0;
        long deleteTime = 0;
        long substringTime = 0;

        for (int i = 0; i < 200; i++) {

            StringBuilder temp = new StringBuilder();
            char[] options = {' ', ' ', ' ', ' ', 'a', 'b', 'c', 'd'};
            for (int j = 0; j < stringLength; j++) {
                temp.append(options[(int) ((Math.random() * 1000)) % options.length]);
            }
            String testStr = temp.toString();

            StringBuilder sb1 = new StringBuilder(testStr);
            StringBuilder sb2 = new StringBuilder(testStr);
            StringBuilder sb3 = new StringBuilder(testStr);

            long timer1 = System.currentTimeMillis();
            trimOriginal(sb1);
            originalTime += System.currentTimeMillis() - timer1;

            long timer2 = System.currentTimeMillis();
            trimDeleteRange(sb2);
            deleteTime += System.currentTimeMillis() - timer2;

            long timer3 = System.currentTimeMillis();
            trimSubstring(sb3);
            substringTime += System.currentTimeMillis() - timer3;
        }

        System.out.println("  original:     " + originalTime + " ms");
        System.out.println("  delete-range: " + deleteTime + " ms");
        System.out.println("  substring:    " + substringTime + " ms");
    }

}

Output:

Main:runAnalysis(string-length=1000)
  original:     0 ms
  delete-range: 4 ms
  substring:    0 ms
Main:runAnalysis(string-length=10000)
  original:     4 ms
  delete-range: 9 ms
  substring:    4 ms
Main:runAnalysis(string-length=100000)
  original:     22 ms
  delete-range: 33 ms
  substring:    43 ms
Main:runAnalysis(string-length=200000)
  original:     57 ms
  delete-range: 93 ms
  substring:    110 ms
Main:runAnalysis(string-length=500000)
  original:     266 ms
  delete-range: 220 ms
  substring:    191 ms
Main:runAnalysis(string-length=1000000)
  original:     479 ms
  delete-range: 467 ms
  substring:    426 ms