• The Idea:
  • Sometimes the records and fields (or rows and columns) are all of the same type allowing one array to be used instead of conformal arrays
• An Example:
  • Data on the heights and weights of a variety of different people

• The Original Data:
  • javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: data)

            double[] heights = { 60.0,  62.0,  65.0,  70.0};
            double[] weights = {100.0, 110.0, 120.0, 140.0};
            

• An Observation:
  • One array could be used to hold all of the elements

javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: concatenate2)

            int n = 4;
            for (int i = 0; i < n; ++i) {
                concatenated[i]   = height[i];
            }

            for (int i = 0; i < n; ++i) {
                concatenated[n + i] = weight[i];
            }
        

javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: interleave)

            int n = 4;
            for (int i = 0; i < n; ++i) {
                interleaved[2 * i]     = height[i];
                interleaved[2 * i + 1] = weight[i];
            }
        

• From record and field to index:
  • javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: toIndex)

                index = (record * recordSize) + field;
            

• From index to record and field:
  • javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: fromIndex)

                record = index / recordSize;
                field  = index % recordSize;
            

• Recall:
  • The main() method of a Java application has a single String[] parameter (commonly named args)
  • When an application is executed from the command line, all of the String objects after the name of the main class are passed to the main() method using this array
• Making Use of the Command Line Arguments:
  • Pass heights and weights into main()

• Finding the Indexes:
  • javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: method)

        /**
         * Calculate the index in an interleaved segmented array
         * from the record number, field number, and record size.
         *
         * @param record      The record number
         * @param field       The field number
         * @param recordSize  The number of fields in a record
         * @return The index
         */
        public static int toIndex(int record, int field, int recordSize) {
            return (record * recordSize) + field;
        }
            

• Converting from String Objects to double Values:
  • javaexamples/programmingpatterns/segmentedarrays/SegmentedArrays.java (Fragment: args3)

            int recordSize = 2;
            int records = args.length / recordSize;
            
            for (int r = 0; r < records; ++r) {
                height[r] = Double.parseDouble(args[toIndex(r, 0, recordSize)]);
                weight[r] = Double.parseDouble(args[toIndex(r, 1, recordSize)]);
            }