如何实现选择排序的基准测试方法？

Question

我尝试测量选择在代码中排序数组的执行时间。选择排序部分正在工作，但基准测试方法"time“甚至没有执行。我的“时间”方法有什么问题，如何让它执行和度量性能时间？

     public class Selection_Sort
{
        public static void main(String[] args)
        {
            // define an array
            int[] array = {12, 3, 7, 6, 2};
            int i;
            int j;
            int t;
            int smallestNumber;


            // run an outer loop i from 0 to array.length-1 to repeat the process of selection sort
            for(i = 0; i < array.length-1; i++)
            {
                // smallest number position
                smallestNumber = i;

                // run an inner loop j for selection sort from i+1 to array.length
                for(j = i + 1; j < array.length; j++)
                {
                    // now check if the value at array[j] is smaller than value at array[smallestNumber]
                    if(array[j] < array[smallestNumber])
                    {
                        // if the value is smaller, then store the value of j to smallestNumber
                        smallestNumber = j;
                    }
                }

                // outside the body of inner loop j check if array[i] > array[smallestNumber]. If yes then swap the numbers
                if(array[i] > array[smallestNumber])
                {
                    t = array[i];
                    array[i] = array[smallestNumber];
                    array[smallestNumber] = t;
                }
            }

            // print the sorted array
            System.out.print("Selection Sort:\n");
            for(i = 0; i < array.length; i++)
            {
                System.out.print(array[i]+" ");
            }
        }

    public static void time(String[] args)
    {
        /* … The code being measured starts … */
        long startTime = System.nanoTime();

        /* … The code being measured ends … */

        long endTime = System.nanoTime();

        // get the difference between the two nano time valuess
        long timeElapsed = endTime - startTime;

        System.out.println("Execution time in nanoseconds: " + timeElapsed);
        System.out.println("Execution time in milliseconds: " + timeElapsed / 1000000);
    }
}

Answer 1

您需要在开始时间和结束时间之间测量代码。一种方法是将要测量的代码部分放在不同的方法中，然后按如下方式调用：

public class Selection_Sort{
public static void sortArray(int[] array)
{

    int smallestNumber;
    int t;

    // run an outer loop i from 0 to array.length-1 to repeat the process of selection sort
    for(int i = 0; i < array.length-1; i++)
    {
        // smallest number position
        smallestNumber = i;

        // run an inner loop j for selection sort from i+1 to array.length
        for(int j = i + 1; j < array.length; j++)
        {
            // now check if the value at array[j] is smaller than value at array[smallestNumber]
            if(array[j] < array[smallestNumber])
            {
                // if the value is smaller, then store the value of j to smallestNumber
                smallestNumber = j;
            }
        }

        // outside the body of inner loop j check if array[i] > array[smallestNumber]. If yes then swap the numbers
        if(array[i] > array[smallestNumber])
        {
            t = array[i];
            array[i] = array[smallestNumber];
            array[smallestNumber] = t;
        }
    }

   
}

  public static void main(String[] args)
  {
      // define an array
      int[] array = {12, 3, 7, 6, 2};
      /* … The code being measured starts … */
      long startTime = System.nanoTime();

      
      sortArray( array);
      /* … The code being measured ends … */

      long endTime = System.nanoTime();

      // get the difference between the two nano time valuess
      long timeElapsed = endTime - startTime;

      System.out.println("Execution time in nanoseconds: " + timeElapsed);
      System.out.println("Execution time in milliseconds: " + timeElapsed / 1000000);
      
      // print the sorted array
      System.out.print("Selection Sort:\n");
      for(int i = 0; i < array.length; i++)
      {
          System.out.print(array[i]+" ");
      }
      
  }
      
  }