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16.8. SkyView - Part B¶

Part b. Write the SkyView method getAverage, which returns the average of the elements of the section of view with row indexes from startRow through endRow, inclusive, and column indexes from startCol through endCol, inclusive.

For example, if nightSky is a SkyView object where view contains the values shown below, the call nightSky.getAverage(1, 2, 0, 1) should return 0.8. (The average is (1.1 + 1.4 + 0.2 + 0.5) / 4, which equals 0.8). The section being averaged is indicated by the dark outline in the table below.

Figure 1: Example values with the region for the getAverage outlined¶

Figure 1: The class information¶

16.8.1. Try and Solve It¶

Finish writing the getAverage method in the class below.

public class SkyView

{
    private double[][] view;

/** Constructs a SkyView object from a 1-dimensional array of scan data.
      * @param numRows the number of rows represented in the view
      * Precondition: numRows > 0
      * @param numCols the number of columns represented in the view
      * Precondition: numCols > 0
      * @param scanned the scan data received from the telescope, stored in telescope order
      * Precondition: scanned.length == numRows * numCols
      * Postcondition: view has been created as a rectangular 2-dimensional array
      * with numRows rows and numCols columns and the values in
      * scanned have been copied to view and are ordered as
      * in the original rectangular area of sky.
      */
    public SkyView(int numRows, int numCols, double[] scanned)
    {
        view = new double[numRows][numCols];
        int scannedIndex = 0;
        for (int r = 0; r < numRows; r++)
        {
            // if even row number go left to right */
            if (r % 2 == 0)
            {
                for (int c = 0; c < numCols; c++)
                {
                    view[r][c] = scanned[scannedIndex];
                    scannedIndex++;
                }
            }
            else {
            for (int c = numCols - 1; c >= 0; c--)
            {
                view[r][c] = scanned[scannedIndex];
                scannedIndex++;
            }
        }
    }

/** Returns the average of the values in a rectangular section of view.
      *
      * @param startRow the first row index of the section
      * @param endRow the last row index of the section
      * @param startCol the first column index of the section
      * @param endCol the last column index of the section
      * Precondition: 0 <= startRow <= endRow < view.length
      * Precondition: 0 <= startCol <= endCol < view[0].length
      * @return the average of the values in the specified section of view */
    public double getAverage(int startRow, int endRow, int startCol, int endCol)
    {
        //*** Finish writing this method! ***
    }

/** This is a main method for testing getAverage */
    public static void main(String[] args)
    {
        double[] startArray = { 0.3, 0.7, 0.8, 0.4, 1.4, 1.1, 0.2, 0.5, 0.1, 1.6, 0.6, 0.9};
        SkyView sView = new SkyView(4,3,startArray);
        System.out.println("getAverage(1,2,0,1) should return 0.8 and returns " + sView.getAverage(1,2,0,1));
     } // end of main

} // end of class

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