Chapter 8 Exercise 1, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

 *8.1 (Sum elements column by column) Write a method that returns the sum of all the elements in a specified column in a matrix using the following header: public static double sumColumn(double[][] m, int columnIndex) Write a test program that reads a 3-by-4 matrix and displays the sum of each column. Here is a sample run:

    Enter a 3-by-4 matrix row by row:
        1.5 2 3 4
        5.5 6 7 8
        9.5 1 3 1
        Sum of the elements at column 0 is 16.5
        Sum of the elements at column 1 is 9.0
        Sum of the elements at column 2 is 13.0
        Sum of the elements at column 3 is 13.0     

import java.util.Scanner;
 
public class ProgramingEx8_1 {
 
 public static void main(String[] args) {
 
  double[][] matrix = new double[3][4];
 
  java.util.Scanner input = new Scanner(System.in);
  System.out.println("Enter a 3-by-4 matrix row by row: ");
  for (int row = 0; row < matrix.length; row++) {
   for (int column = 0; column < matrix[row].length; column++) {
    matrix[row][column] = input.nextDouble();
   }
  }
 
  for (int column = 0; column < matrix[0].length; column++) {
   System.out.println("Sum of the elements at column " + column
     + " is " + sumColumn(matrix, column));
  }
 
 }
 
 public static double sumColumn(double[][] m, int columnIndex) {
 
  double sum = 0;
  for (int row = 0; row < m.length; row++) {
   sum += m[row][columnIndex];
  }
  return sum;
 }
 
}