Bài tập Java - Viết chương trình java tính hàm SLOPE trong excel

SLOPE(known_y's, known_x's)

package vn.viettuts;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class Common {
    public static final long MILLI_SECOND_PER_DAY = 60 * 60 * 24 * 1000;
    public static final String DATE_FOMART = "MM/dd/yyyy";
    
    /**
     * tinh slope theo cong thuc slope=∑(x-averageX)(y-averageY)/∑(x-averageX)^2
     * trong do: averageX la gia tri trung binh cua listX
     *           averageY la gia tri trung binh cua listY
     *
     * @param listY: danh sach so thuc
     * @param listX: danh sach so thuc
     * @return slope cua listX va listY
     * @throws ParseException
     */
    public static float slope(List<Float> listY, List<Float> listX) 
            throws ParseException {
        float averageX;
        float averageY;
        float totalX = 0;
        float totalY = 0;
        float totalAX_AY = 0;
        float totalAX_AX = 0;
        int i;

        // tinh tong cot x va y
        for (i = 0; i < listX.size(); i++) {
            totalX = totalX + listX.get(i);
            totalY = totalY + listY.get(i);
        }
        // tinh gia tri trung binh cua listX va listY
        averageX = totalX / listX.size();
        averageY = totalY / listX.size();

        for (i = 0; i < listX.size(); i++) {
            // tinh tong (x-averageX)*(y-averageY)
            totalAX_AY = totalAX_AY 
                    + ((listX.get(i) - averageX) * (listY.get(i) - averageY));
            // tinh tong (x-averageX)^2
            totalAX_AX = totalAX_AX 
                    + ((listX.get(i) - averageX) * (listX.get(i) - averageX));
        }
        // return slope cua day so x va day so y
        return totalAX_AY / totalAX_AX;
    }

    /**
     * chuyen doi danh sach date dang chuoi thanh danh sach so thuc
     * voi quy uoc min date (day) = 1.0
     * 
     * @param listStrDates: danh sach date dang chuoi
     * @return List<Float>: danh sach so thuc
     * @throws ParseException
     */
    public static List<Float> parseDateToFloats(List<String> listStrDates) 
            throws ParseException {
        List<Date> listDates = new ArrayList<>();
        List<Float> listY = new ArrayList<>();
        
        // phan tich string thanh date
        listDates = parseStringToDates(listStrDates);
        Date minDate = listDates.get(0);

        // tim min date
        for (Date date : listDates) {
            if (minDate.getTime() > date.getTime()) {
                minDate = date;
            }
        }

        // chuyen doi date thanh so thuc voi quy uoc min date (day) = 1.0
        for (Date date : listDates) {
            listY.add((float) (
                    (date.getTime() - minDate.getTime()) / MILLI_SECOND_PER_DAY) 
                    + 1.0F);
        }
        
        return listY;
    }
    
    /**
     * phan tich list string thanh list date
     * 
     * @param listStrDates: list date dang string
     * @return List<Date>
     * @throws ParseException
     */
    public static List<Date> parseStringToDates(List<String> listStrDates) 
            throws ParseException {
        List<Date> listDates = new ArrayList<>();
        SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FOMART);

        for (String strDate : listStrDates) {
            listDates.add(dateFormat.parse(strDate.trim()));
        }

        return listDates;
    }
}

package vn.viettuts;

import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        float slope;
        List<String> listStrDates = new ArrayList<>();
        List<Float> listY = new ArrayList<>();
        List<Float> listX = new ArrayList<>();

        try {
            // add gia tri cho listStrDates
            listStrDates.add("12/19/2017");
            listStrDates.add("12/18/2017");
            listStrDates.add("1/2/2018");
            // chuyen doi listStrDates sang dang so listY
            listY = Common.parseDateToFloats(listStrDates);
            // define listX
            listX.add(4F);
            listX.add(1F);
            listX.add(2F);
            // tinh slope cua listY va listX
            slope = Common.slope(listY, listX);
            System.out.println(slope);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}