Addition of diagonals of a matrix using array in Java

This is my 2nd exercise for my Java Programming Lab

[ZeeshanJamal]

Hi. why did you use (i+j==2) for the second diagonal?

[suubilnaamtii]

Please sir, I need help with this
Design an Object Oriented program in JAVA to obtain the first 9 odd numbers from a user and store in a file “output.txt” in a matrix form (3 X 3). Read the file and store the items in a 2D 3x3 array then compute the difference between the product of the leading diagonal and the product of the trailing diagonal. The output of the computation should be written to the file “outputfile.txt”.
b. Draw the class diagrams of all your classes
NOTE: The program MUST have at least 2 classes.

[mahnoorawan]

Salam sir
I am from Pakistan are u help me