The Java program in TimeStringConcat.java calculates the time is takes
to build up a String of length n by repeatedly concatenating one
character at a time to the String.

The program takes 3 command-line parameters: the value n for the size
of Strings to construct, the number of times to repeat the experiment
to improve the accuracy of the timings, and a number, 0 or 1, which
turns off or on a verbose output mode.

To compile and run the program at the Unix command line (or a DOS
prompt, or a Mac Terminal window), one would issue the command

javac TimeStringConcat.java

to compile to TimeStringConcat.class, then run the program with

java TimeStringConcat 128 1000 0

(for example) to run the program for n=128, repeat 1000 times, and
verbose mode off.

When verbose mode is on, a few lines of output are printed about the
timings computed.  When verbose mode is off, it simply prints the
value of n followed by the computed average time (in nanoseconds) for
one instance of the String creation.

The Bash script run_timings.sh runs the program 100 times: 10 each
with values of n for all powers of 2 from 16 to 8192.  If one wanted
to capture the output of all 100 runs to a file "timings.out", the
command

./run_timings.sh > timings.out

would do the job, and would produce a file with 100 lines, suitable
for postprocessing into appropriate tabular or graphical forms.