记录几个测试算法性能的工具类,方便以后测试算法.

Stopwatch类:可以得到算法的执行时间(单位:s,小数点后3位)

   1: public class Stopwatch {

   2:     private long start;

   3:     

   4:     public Stopwatch() {

   5:         start = System.currentTimeMillis();

   6:     }

   7:     

   8:     public double elapsedTime(){

   9:         long now = System.currentTimeMillis();

  10:         return (now - start) / 1000.0;

  11:     }

  12: }

具体使用方法:

   1: public static void main(String[] args) {

   2:         Stopwatch timer = new Stopwatch();

   3:          /*调用某个算法*/

   4:         double spend = timer.elapsedTime();

   5:         /*spend就是调用的算法消耗的时间*/

   6:     }

例如:测试选择排序和插入排序的性能

   1: public class SortCompare {

   2:     public static double time(String alg,Comparable[] a){

   3:         Stopwatch timer = new Stopwatch();

   4:         

   5:         if("Insert".equals(alg) || "Insertion".equals(alg)) 

   6:             new Insertion().sort(a);

   7:         else if("Select".equals(alg) || "Selection".equals(alg)) 

   8:             new Selection().sort(a);

   9:         /*此处还可以添加其他的排序算法*/

  10:         

  11:         return timer.elapsedTime();

  12:     }

  13:     

  14:     public static double timeRandomInput(String alg,int times,int length){

  15:         double total = 0.0;

  16:         Double[] a = new Double[length];

  17:         for(int i = 0;i<times;i++){

  18:             for(int j = 0;j<length;j++)

  19:                 a[j] = StdRandom.uniform();

  20:             total += time(alg, a);

  21:         }

  22:         return total;

  23:     }

  24:     

  25:     public static void main(String[] args) {

  26:         String alg1 = args[0];

  27:         String alg2 = args[1];

  28:         int times = Integer.parseInt(args[2]);

  29:         int length = Integer.parseInt(args[3]);

  30:         double t1 = timeRandomInput(alg1, times, length);

  31:         double t2 = timeRandomInput(alg2, times, length);

  32:         StdOut.printf("For %d randomDoubles \n   %s is ", length,alg1);

  33:         StdOut.printf("%.1f times faster than %s\n", t2/t1,alg2);

  34:     }

  35: }

测试结果

可以看出结果大致在1~3之间….

总结:
在测试或者比较算法的性能时，可以以SortCompare为模板,比较不同算法之间的差异.