we have to go upto 0 to array.lenght-1, because of indexing
         of array.
          we are comparing each value which is greater than i th index,
          with current i th value , for finding the maximum value in array.
          if array[j] is less than array[max] than j value will be assign into
          the max variable
          while calling function we should give two parameter
          first one starting index of array - that is zero
          second one is ending index of array - that is this.a.length-1.
          second time of calling qsort function in recursion
          there should be start from q+1 index and end with r.
          Whole description is there for issue.