Question

Write a method that returns the sum of all the elements in a specified column in a 3 x 4 matrix using the following header:

public static double sumColumn(double[][] m, int columnIndex)

The program should be broken down into methods, menu-driven, and check for proper input, etc.

The problem I'm having is I'm trying to get my menu to execute the runProgram method. I'm not sure what should be in the parentheses to direct choice "1" to the method. I'm sure I'll also have that problem with executing choice "2," which should go to the sumColumn method, but I'm not there yet. I'll also need a test method. I'd appreciate any help. Here's my code:

package sumelements;

import java.util.Scanner;
public class SumElements
{

private final static Scanner myScan = new Scanner(System.in);

  
//=================void main=====================================================
public static void main(String[] args)
{
char choice;
  
do
{
choice = GetMenu();
switch(choice)
{
case '1':
{
runProgram();
break;
}
case '2':
{
  
break;
}
case '3':
{
System.out.println("Thanks for using ACME products.\n");
break;
}
default:
{
System.out.println("Invalid input. Please re-enter.\n");
choice = GetMenu();
}
}
}while(choice != '3');
}
  
//===============GetMenu=========================================================
private static char GetMenu()
{
System.out.print("=================================\n"
+ " Acme Element Adder \n"
+ "\t(1) Input a 3 x 4 matrix \n "
+ "\t(2) Test system with random number \n"
+ "\t(3) Quit the program\n"
+ "\t Make your choice: ");
  
char choice = myScan.next().toUpperCase().charAt(0);
return choice;
}
  
public static void runProgram();
{
double arr[][]=new double[3][4];

System.out.println("Enter a 3-by-4 matrix row by row: ");

for(int i=0;i<3;i++)
{
for(int j=0;j<4;j++)
{
arr[i][j]=myScan.nextDouble();
}
}

for(int i=0;i<4;i++)
{
System.out.println("Sum of the element at column "+i+" is "+sumColumn(arr,i));
}
}

public static double sumColumn(double[][]m,int ColumnIndex)
{
double sum=0;

for(int i=0;i<3;i++)
{
sum+=m[i][ColumnIndex];
}
  
return sum;
}
}

Answer 1

JAVA CODE:

import java.util.*;

public class SumElements {

    // Scanner

    private final static Scanner myScan = new Scanner(System.in);

    public static void main(String[] args){

        // Declare int variable for choice

        int choice;

        while(true){

            // calling GetMenu() function get the choice

            choice = GetMenu();

            // enter choice in the switch case

            switch(choice)

            {

                case 1:

                {

                    // calling runProgram() function

                    runProgram();

                    break;

                }

                case 2:

                {  

                    // calling runProgramRandomNumber() function

                    runProgramRandomNumber();

                    break;

                }

                case 3:

                {   // Display the message

                    System.out.println("Thanks for using ACME products.\n");

                    return;// exit program

                }

                default:

                {   // display message for invalid choice

                    System.out.println("Invalid input. Please re-enter.\n");

                }

            }

        }   

    }

    // Define GetMenu() method

    // This method take the choice from the user

    private static int GetMenu()

    {

        System.out.print("\n=================================\n"

                          + " Acme Element Adder \n"

                          + "\t(1) Input a 3 x 4 matrix \n "

                          + "\t(2) Test system with random number \n"

                          + "\t(3) Quit the program\n"

                          + "\t Make your choice: ");

        // ask for input choice

        int choice = myScan.nextInt();

        return choice;// return choice

    }

    // Define runProgram() method

    public static void runProgram()

    {

        // Declare double 3 x 4 array

        double arr[][]=new double[3][4];

        System.out.println("Enter a 3-by-4 matrix row by row: ");

        // Enter the element

        for(int i=0;i<3;i++)

        {

            for(int j=0;j<4;j++)

            {

                arr[i][j]=myScan.nextDouble();

            }

        }

        // iterate for loop for Sum of the element at column

        for(int i=0;i<4;i++)

        {

            // calling sumColumn() method and display

            System.out.println("Sum of the element at column "+i+" is "+sumColumn(arr,i));

        }

    }

    // Define runProgramRandomNumber() method

    public static void runProgramRandomNumber()

    {

        // Declare double 3 x 4 array

        double arr[][]=new double[3][4];

        System.out.println("Generating random number 3-by-4 matrix : ");

        // Random number object

        Random rand = new Random();

        for(int i=0;i<3;i++)

        {

            for(int j=0;j<4;j++)

            {   // generate random number and them insert into matrix

                arr[i][j]=rand.nextInt(10);

            }

        }

        // Display the 3 x 4 matrix

        for(int i=0;i<3;i++)

        {

            for(int j=0;j<4;j++)

            {

                System.out.print((int)arr[i][j]+" ");

            }

            System.out.println();

        }

        // Iterate for loop

        for(int i=0;i<4;i++)

        {

            // calling sumColumn() method and display

            System.out.println("Sum of the element at column "+i+" is "+sumColumn(arr,i));

        }

    }

    // Define sumColumn() method

    // pass the parameter 3 x 4 metrix and ColumnIndex

    public static double sumColumn(double[][]m,int ColumnIndex)

    {

        // Declare sum variable

        double sum=0;

        for(int i=0;i<3;i++)

        {

            // calculate the sum of specific column

            sum+=m[i][ColumnIndex];

        }

        // return sum

        return sum;

    }

}

OUTPUT:

NOTE: If you don't understand any step please tell me.