COS126

• Download Stopwatch.java

/*************************************************************************
 * Name:
 * Login:
 * Precept:
 *
 * Description: The test client compares the method for computing square
 * roots in Java's Math library with our implementation from Program 2.1.1
 * which uses Newton's method for the task of computing the sum of the
 * square roots of the numbers from 0 to N-1. For this quick test,
 * the Java implementation Math.sqrt() is about 20 times faster than 
 * our Newton.sqrt() (as it should be!).
 *
 * Dependencies: None.
 *
 * Remarks: This code is from book section 3.2.
 *************************************************************************/

public class Stopwatch { 

    // start keeps track of the time the stopwatch was created
    private final long start;

    // constructors initialize instance variables
    public Stopwatch() {
        start = System.currentTimeMillis();
    } 

    // return time (in seconds) since this object was created
    public double elapsedTime() {
        long now = System.currentTimeMillis();
        return (now - start) / 1000.0;
    } 

    public static void main(String[] args) { 
        int N = Integer.parseInt(args[0]); 

        // time Math library implementation
        double totalMath = 0.0; 
        Stopwatch swMath = new Stopwatch(); 
        for (int i = 0; i < N; i++) {
            totalMath += Math.sqrt(i); 
        }
        double timeMath = swMath.elapsedTime(); 
  
        // time Newton's method implementation
        double totalNewton = 0.0; 
        Stopwatch swNewton = new Stopwatch(); 
        for (int i = 0; i < N; i++) {
            totalNewton += Newton.sqrt(i);
        }

        // print results
        double timeNewton = swNewton.elapsedTime(); 
        StdOut.println(totalNewton/totalMath); 
        StdOut.println(timeNewton/timeMath); 
    }
}