Time taken by various string concatenation methods

As the title goes, the objective of the folowing program will be to find out the time difference or performance various string concatenation methods:

i) + operator

ii) String class' concat() method

iii) StringBuffer class' append() method

iv) StringBuilder class' append() method

The program is followed by results in nanoseconds.

Before recording the results, I have warmed up the JVM by running the code multiple times (~10). Part 2 will follow soon, the link will be provided at the end of this article whenever posted.

Assumtions made by us (precisely, what we knew!):

1. + operator takes a lot of time, as each String will be converted to StringBuilder object and other concatenated strings will be appended and at the last, toString() method will be called on that StringBuilder object. For example,

String str = "1";
str = str + "2" + "3";

will result in

StringBuilder message = new StringBuilder();
message.append("1");
message.append("2");
message.append("3");
String str = message.toString();

2. concat() method does nothing special, just concatenates.

3. Each manipulation through above two processes require a new String object to be created.

4. StringBuffer is synchronized, so each time, lock will be acquired on the operated object, and then released.

5. StringBuilder is most preferable, as it is not synchronized and will save on creating a lot of objects.

package in.blogspot.javabambino.string;

/**
 * This class returns the time duration for a process in nanosecs.
 * @author xploreraj
 *
 */
class TimeUtil {
 private long startTime;
 TimeUtil(){
  startTime = System.nanoTime();
 }
 
 public long getElapsedTimeNanos(){
  return System.nanoTime() - startTime;
 }
}

/**
 * This class measures the performance of various string
 * concatenation operations.
 * @author xploreraj
 *
 */
public class ConcatStringPerf {
 private static int iterationCount = 5;
 public static void main(String[] args) {

  // using + operator
  String str = "1";
  TimeUtil timeUtil = new TimeUtil();
  for(int i=1; i<=iterationCount; i++){
   str = str + "*";
  }
  System.out.println(timeUtil.getElapsedTimeNanos() + 
    " ns taken over " + iterationCount + 
    " iterations using +");

  //using + operator again but without loop

  TimeUtil timeUtil1 = new TimeUtil();
  String strr = "6" + ")" + ")" + ")" + ")" + ")";
  System.out.println(timeUtil1.getElapsedTimeNanos() + 
    " ns when +ed manually 5 times without loop");

  // using String class' concat() method

  String str2 = "2";
  TimeUtil timeUtil2 = new TimeUtil();
  for(int i=1; i<=iterationCount; i++){
   str2 = str2.concat("$");
  }
  System.out.println(timeUtil2.getElapsedTimeNanos() + 
    " ns taken over " + iterationCount + 
    " iterations using String concat");

  // using StringBuffer class' append() method

  StringBuffer buffer = new StringBuffer("3");
  TimeUtil timeUtil3 = new TimeUtil();
  for(int i=1; i<=iterationCount; i++){
   buffer = buffer.append("#");
  }
  System.out.println(timeUtil3.getElapsedTimeNanos() + 
    " ns taken over " + iterationCount + 
    " iterations using StringBuffer append");

  // using StringBuilder class' append() method
 
  StringBuilder builder = new StringBuilder("2");
  TimeUtil timeUtil4 = new TimeUtil();
  for(int i=1; i<=iterationCount; i++){
   builder = builder.append("&");
  }
  System.out.println(timeUtil4.getElapsedTimeNanos() + 
    " ns taken over " + iterationCount + 
    " iterations using StringBuilder append");
 }
}

Results: Who won?

i) Machine specs: Win 7, 32 bit, intel Core2Duo, 2.2GHz, 3GB RAM

   JVM: JDK 1.6.0_18

Result	Run 1	Run 2	Run 3	Run 4		Run 5	Run 6
ns taken over 5 iterations using +	72325	68592	76524		76524	76524	75125
ns when +ed manually 5 times without loop	4200	4200	5133		5133	4200	8399
ns taken over 5 iterations using String concat	27997	31730	202043		27064	29397	30330
ns taken over 5 iterations using StringBuffer append	8865	9332	9332		11199	10732	9333
ns taken over 5 iterations using StringBuilder append	631327	642059	861367		1225325	1229991	1973305

ii) Machine specs: Win XP, 32 bit, intel Core i5, 3.2 GHz, 4GB RAM

    JVM: JDK 1.6.0_20 

Result	Run 1	Run 2	Run 3	Run 4		Run 5	Run 6
ns taken over 5 iterations using +	39441	38842	38466		43310	39190	38588
ns when +ed manually 5 times without loop	10002	4249	7808		14164	4294	4770
ns taken over 5 iterations using String concat	15837	35596	32029		19999	47936	28200
ns taken over 5 iterations using StringBuffer append	10435	10657	10803		7190	7491	14412
ns taken over 5 iterations using StringBuilder append	14106	66758	14062		6805	14338	12147

iii) Machine Specs: Win XP, 32 bit, intel Core i5, 3.2 GHz, 4GB RAM;  with -server switch on [java -server ConcatStringPerf ]

     JVM: JDK 1.6.0_20 

Result	Run 1	Run 2	Run 3	Run 4		Run 5	Run 6
ns taken over 5 iterations using +	34487	34445	34431		48864	34424	35019
ns when +ed manually 5 times without loop	10650	2765	2957		3375	2992	4475
ns taken over 5 iterations using String concat	12839	22008	59841		23023	78406	26371
ns taken over 5 iterations using StringBuffer append	16288	15982	15446		12670	10999	16678
ns taken over 5 iterations using StringBuilder append	13660	4197	4255		3761	3827	14737

Please do post anything relevant and researched, and all important points will be compiled in Part 2 of this article. For the time-being, you can read an abstract article on string concatenation here.