Assume that mat in a N by N 2D array that stores N2 integers
Solution
import java.util.Scanner;
 class sub
 {
 public static void main(String args[])
 {
 int n,i,j,csum,rsum,sum;
 Scanner sc=new Scanner(System.in);
 n=sc.nextInt();
 int mat[][]=new int[n][n]; //matrix creation
 System.out.println(\"enter the array elemets\");
 for(i=0;i<n;i++)
 {
 for(j=0;j<n;j++)
 {
 mat[i][j]=sc.nextInt();
 }
 }
 //a.sum of the last column integers
 System.out.println(\"sum of the last column itegers\") ;
 csum=0;
 for(i=n;i>n;i++)
 {
   
 for(j=0;j<n;j++)
 {
 csum=csum+mat[i][j];
 }
 }
 System.out.println(\"sum of the last column is:\"+csum);
 //b.sum of the first row inteegers
 System.out.println(\"sum of the first row of integers i mat\");
 rsum=0;
 for(i=0;i<0;i++)
 {
   
 for (j=0;j<n;j++)
 {
 rsum=rsum+mat[i][j] ;
 }
 }
 System.out.println(\"sum of the first row is:\"+rsum);
 //c.sum of diagonal integers
 System.out.println(\"sum of the diagonal matrix\");
 sum=0;
 for(i=0,j=0;i<n&&j<n;i++,j++)
 {
 sum=sum+mat[i][j];
 }
 System.out.println(\"sum of the diagonal elements :\"+sum);
 }
 }

