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When read this post, TRIM, LTRIM and RTRIM in Java

I have a doubt about the performance difference between the one uses regular expression ltrim and the straightforward ltrim3. So I use Guava topwatch
to test their performance. 
Guava Usage
1. Use Stopwatch static factory method to create one instance.
Stopwatch stopwatch = Stopwatch.createStarted()
2. Use stopwatch.elapsed(TimeUnit) to get elapsed time.
3. We can reuse same stopwatch instance to measures another operation, but we have to first call reset(), and start().
reset() method would reset internal variable: elapsedNanos=0, isRunning=false. Calling start() would start again to measure time elapsed.
Conclusion
The test result is as what I expected, the straightforward one gives the best performance.
458 for ltrim3(the straightforward one)
3967 for ltrim(using regular expression)

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The code looks like below:

import com.google.common.base.Stopwatch;

public class LTrimTester {
  private final static Pattern LTRIM = Pattern.compile("^\\s+");
  private final static Pattern RTRIM = Pattern.compile("\\s+$");

  public static void main(String[] args) {
    int times = 10000000;
    Stopwatch stopwatch = Stopwatch.createStarted();
    for (int i = 0; i < times; i++) {
      String str = "  hello world  ";
      ltrim(str);
    }
    System.out.println(stopwatch.elapsed(TimeUnit.MILLISECONDS)
        + " for ltrim(using regular expression)");

    stopwatch.reset();
    stopwatch.start();
    for (int i = 0; i < times; i++) {
      String str = "  hello world  ";
      ltrim3(str);
    }
    System.out.println(stopwatch.elapsed(TimeUnit.MILLISECONDS)
        + " for ltrim3(the straightforward one)");
    stopwatch.stop();
  }

  public static String ltrim(String s) {
    return LTRIM.matcher(s).replaceAll("");
  }

  public static String ltrim3(String s) {
    int i = 0;
    while (i < s.length() && Character.isWhitespace(s.charAt(i))) {
      i++;
    }
    return s.substring(i);
  }
}

Resources
TRIM, LTRIM and RTRIM in Java
Guava Stopwatch Javadoc
Guava Stopwatch

via Blogger http://lifelongprogrammer.blogspot.com/2013/12/using-guava-stopwatch.html

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