# Java Program to Find the Sums of Primary Diagonal and Secondary Diagonal

In the previous article, we have discussed Java Program to find the Difference Between Sums of Two Diagonals of a Matrix

In this article we are going to see how we can find the sums of Primary Diagonal and Secondary Diagonal of the matrix in JAVA language.

## Java Program to Find the Sums of Primary Diagonal and Secondary Diagonal

A 3*3 Matrix is having 3 rows and 3 columns where this 3*3 represents the dimension of the matrix. Means there are 3*3 i.e. total 9 elements in a 3*3 Matrix.

Let’s understand it in more simpler way.

                   | A00   A01   A02 |
Matrix A =  | A10   A11   A12 |
| A20   A21   A22 | 3*3
• Matrix A represents a 3*3 matrix.
• A‘ represents the matrix element
• Aij‘ represents the matrix element at it’s matrix position/index.
• i‘ represents the row index
• j‘ represents the column index
• Means A00=Aij  where i=0 and j=0,  A01=aij where i=0 and j=1 and like this.
• Here we have started row value from 0 and column value from 0.

Let’s see different ways to find sums of Primary Diagonal and Secondary Diagonal of the matrix in JAVA language.

### Method-1: Java Program to Find the Sums of Primary Diagonal and Secondary Diagonal By Static Initialization of Array Elements

Approach:

• Initialize an array of size 3×3 with values.
• Show the array to the user.
• Similarly use two for loops to iterate the rows and columns, then calculate the main diagonal sum.
• Repeat the above step to calculate the counter diagonal sum.
• Add both of them and print the output.

Program:

import java.util.Scanner;

public class Matrix
{
public static void main(String args[])
{
//Scanner class to take input
Scanner scan = new Scanner(System.in);

// Initializing the 3X3 matrix i.e. 2D array
int arr[][] = {{19,25,32},{40,54,62},{70,20,60}}, mainSum = 0, counterSum = 0;
int row, col;

System.out.print("The array elements are : ");

// Loop to print the elements
for(row=0;row<3;row++)
{
// Used for formatting
System.out.print("\n");
for(col=0;col<3;col++)
{
System.out.print(arr[row][col]+" ");
}
}
System.out.print("\n");

// Loop to take the sum of main diagonal elements
for(row=0;row<3;row++)
for(col=0;col<3;col++)
{
if(row==col)
mainSum+=arr[row][col];
// if(row+col==2)
}

// Loop to take the sum of counter diagonal elements
for(row=0;row<3;row++)
for(col=0;col<3;col++)
{
if(row+col==2)
counterSum+=arr[row][col];
}

// Printing both the diagonals sum
System.out.println("\nThe sum of both diagonals are : "+(mainSum+counterSum));
}
}


Output:

The array elements are :
19 25 32
40 54 62
70 20 60

The sum of both diagonals are : 289

### Method-2: Java Program to Find the Sums of Primary Diagonal and Secondary Diagonal By Dynamic Initialization of Array Elements

Approach:

• Initialize an array of size 3×3.
• Ask the user for input of array elements.
• Use two for loops to iterate the rows and columns to input the array elements.
• Show the array to the user.
• Similarly use two for loops to iterate the rows and columns, then calculate the main diagonal sum.
• Repeat the above step to calculate the counter diagonal sum.
• Add both of them and print the output.

Program:

import java.util.Scanner;

public class matrix
{
public static void main(String args[])
{
//Scanner class to take input
Scanner scan = new Scanner(System.in);

// Initializing the 3X3 matrix i.e. 2D array
int arr[][] = new int[3][3];

System.out.println("Enter the 3x3 matrix elements :");
int row, col, mainSum = 0, counterSum = 0;
// Loop to take user input
for(row=0;row<3;row++)
for(col=0;col<3;col++)
arr[row][col] = scan.nextInt();

System.out.print("The array elements are : ");

// Loop to print the elements
for(row=0;row<3;row++)
{
// Used for formatting
System.out.print("\n");
for(col=0;col<3;col++)
{
System.out.print(arr[row][col]+" ");
}
}
System.out.print("\n");

// Loop to take the sum of main diagonal elements
for(row=0;row<3;row++)
for(col=0;col<3;col++)
{
if(row==col)
mainSum+=arr[row][col];
// if(row+col==2)
}

// Loop to take the sum of counter diagonal elements
for(row=0;row<3;row++)
for(col=0;col<3;col++)
{
if(row+col==2)
counterSum+=arr[row][col];
}

// Printing both the diagonals sum
System.out.print("\nThe sum of both diagonals is "+(mainSum+counterSum));
}
}


Output:

Enter the 3x3 matrix elements : 1 2 3 4 5 6 7 8 9
The array elements are :
1 2 3
4 5 6
7 8 9

The sum of both diagonals is 30

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