1. Test two algorithms provided in class StringExperiment of composing a string with two different ways: (a) with the use of StringBuilder and (b) with copies of characters. a. For this practice, you would need to change some related parameters such that the execution times for both can be completed with a range of 1~3 minutes and that the real time for concatenation can correctly reflect the right big-Oh evaluations. b. You would need to jot down the time vs data size and figure out the big-Oh functions for the algorithms.

public class StringExperiment {

/** Uses repeated concatenation to compose a String with n copies of character c. */ public static String repeat1(char c, int n) { String answer = ""; for (int j=0; j < n; j++) answer += c; return answer; }

/** Uses StringBuilder to compose a String with n copies of character c. */ public static String repeat2(char c, int n) { StringBuilder sb = new StringBuilder(); for (int j=0; j < n; j++) sb.append(c); return sb.toString(); }

/** * Tests the two versions of the 'repeat' algorithm, doubling the * size of n each trial, beginning with the given start value. The * first command line argument can be used to change the number of * trials, and the second to adjust the start value. */ public static void main(String[] args) { int n = 50000; // starting value int trials = 10; try { if (args.length > 0) trials = Integer.parseInt(args[0]); if (args.length > 1) n = Integer.parseInt(args[1]); } catch (NumberFormatException e) { } int start = n; // remember the original starting value

// let's run version 2 (the quicker one) first System.out.println("Testing repeat2..."); for (int t=0; t < trials; t++) { long startTime = System.currentTimeMillis(); String temp = repeat2('-', n); long endTime = System.currentTimeMillis(); long elapsed = endTime - startTime; System.out.println(String.format("n: %9d took %12d milliseconds", n, elapsed)); n *= 2; // double the problem size }

System.out.println("Testing repeat1..."); n = start; // restore n to its start value for (int t=0; t < trials; t++) { long startTime = System.currentTimeMillis(); String temp = repeat1('-', n); long endTime = System.currentTimeMillis(); long elapsed = endTime - startTime; System.out.println(String.format("n: %9d took %12d milliseconds", n, elapsed)); n *= 2; // double the problem size } } }