Question

I am currently attempting to revise a Java Homework program for my Data Structures class that displays the output of the MaxSumTest program in a table.

I’ve created four arrays, and placed them inside one of the loops that calculates the timing info. I am trying to populate each array with only the timing info for one algorithm. So each array would have 4 elements. However, every time I run my revision of the program, I get an out of bounds error.

Here is the Original

The only method I revised is getTimingInfo. Here is my revision:

public static void getTimingInfo( int n, int alg )
{
    int [] test = new int[ n ];

    long startTime = System.currentTimeMillis( );;
    long totalTime = 0;



   //create an array for each Algorithm
    long[] alg4;
    long[] alg3;
    long[] alg2;
    long[] alg1;

    //allocate memory for 5 long ints 

    alg4 = new long[5];
    alg3 = new long[5];
    alg2 = new long[5];
    alg1 = new long[5];

   int i;
   int j;
   int index = 0;

   for( i = 0; totalTime < 4000; i++ )
   {
       for( j = 0; j < test.length; j++ )
           test[ j ] = rand.nextInt( 100 ) - 50;
    index = j;
       switch( alg )
       {
         case 1:
           maxSubSum1( test );
           break;
         case 2:
           maxSubSum2( test );
           break;
         case 3:
           maxSubSum3( test );
           break;
         case 4:
           maxSubSum4( test );
           break;
       }

       totalTime = System.currentTimeMillis( ) - startTime;

   }

    alg1[index] = totalTime * 1000 / i;
    alg2[index] = totalTime * 1000 / i;
    alg3[index] = totalTime * 1000 / i;
    alg4[index] = totalTime * 1000 / i;

    //Build first column of table
    System.out.println("Size of N Algorithms\t" + "250\t" + "2500\t" + "25000\t" + "250000");

    System.out.println("Alg #4\t" + alg4[0] + "\t" + alg4[1] + "\t" + alg4[2] + "\t" + alg4[3] + "\t" + alg4[4]);
    System.out.println("Alg #3\t" + alg3[0] + "\t" + alg3[1] + "\t" + alg3[2] + "\t" + alg3[3] + "\t" + alg3[4]);
    System.out.println("Alg #2\t" + alg2[0] + "\t" + alg2[1] + "\t" + alg2[2] + "\t" + alg2[3] + "\t" + alg2[4]);
    System.out.println("Alg #1\t" + alg1[0] + "\t" + alg1[1] + "\t" + alg1[2] + "\t" + alg1[3] + "\t" + alg1[4]);


    /*

    System.out.println( "Algorithm #" + alg + "\t"
         + "N = " + test.length
         + "\ttime = " + ( totalTime * 1000 / i ) + " microsec" );
    */


 }

Any advice or pointers in the right direction would be appreciated.

Answer 1

I’m not sure exactly what you are trying to do, but I think that what you really want to do is call getTimingInfo() a number of times and then assign the results to a table, not change the internal workings of getTimingInfo().

This requires that you define the arrays in which you will store the timing data OUTSIDE of getTimingInfo(), and then the only change inside of getTimingInfo() would be storing to that (already defined) array, rather than printing.