Question

Simulate Stopwatch Program​

Answer 1

Below is the syntax highlighted version of Stopwatch.java from § Standard Libraries.   Here is the Javadoc.

/****************************************************************************** * Compilation: javac Stopwatch.java * Execution: java Stopwatch n * Dependencies: none * * A utility class to measure the running time (wall clock) of a program. * * % java8 Stopwatch 100000000 * 6.666667e+11 0.5820 seconds * 6.666667e+11 8.4530 seconds * ******************************************************************************//** * The {@code Stopwatch} data type is for measuring * the time that elapses between the start and end of a * programming task (wall-clock time). * * See {@link StopwatchCPU} for a version that measures CPU time. * * @author Robert Sedgewick * @author Kevin Wayne */public class Stopwatch { private final long start; /** * Initializes a new stopwatch. */ public Stopwatch() { start = System.currentTimeMillis(); } /** * Returns the elapsed CPU time (in seconds) since the stopwatch was created. * * @return elapsed CPU time (in seconds) since the stopwatch was created */ public double elapsedTime() { long now = System.currentTimeMillis(); return (now - start) / 1000.0; } /** * Unit tests the {@code Stopwatch} data type. * Takes a command-line argument {@code n} and computes the * sum of the square roots of the first {@code n} positive integers, * first using {@code Math.sqrt()}, then using {@code Math.pow()}. * It prints to standard output the sum and the amount of time to * compute the sum. Note that the discrete sum can be approximated by * an integral - the sum should be approximately 2/3 * (n^(3/2) - 1). * * @param args the command-line arguments */ public static void main(String[] args) { int n = Integer.parseInt(args[0]); // sum of square roots of integers from 1 to n using Math.sqrt(x). Stopwatch timer1 = new Stopwatch(); double sum1 = 0.0; for (int i = 1; i <= n; i++) { sum1 += Math.sqrt(i); } double time1 = timer1.elapsedTime(); StdOut.printf("%e (%.2f seconds)\n", sum1, time1); // sum of square roots of integers from 1 to n using Math.pow(x, 0.5). Stopwatch timer2 = new Stopwatch(); double sum2 = 0.0; for (int i = 1; i <= n; i++) { sum2 += Math.pow(i, 0.5); } double time2 = timer2.elapsedTime(); StdOut.printf("%e (%.2f seconds)\n", sum2, time2); }}