Magic Squares

 One interesting application of two-dimensional arrays is magic squares. 
 A magic square is a square matrix in which the sum of every row, every
 column, and both diagonals is the same. Magic squares have been studied
 for many years, and there are some particularly famous magic squares. 
 In this exercise you will write code to determine whether a square is magic. 

 File Square.java contains the shell for a class that represents a square
 matrix. It contains headers for a constructor that gives the size of the
 square and  methods to read values into the square, print the square, find
 the sum of a  given row, find the sum of a given column, find the sum of
 the main (or other) diagonal, and determine whether the square is magic. 
 The read method is given for you; you will need to write the others. 

 File SquareTest.java contains the shell for a program that reads input for 
 squares from a file and tells whether each square is a magic square.

 Following the comments, fill in the remaining code. Run your program on file
 magicData.txt. You should find that the first, second, and third squares in
 the input are magic, and that the rest (fourth through seventh) are not.
 Note that the -1 at the bottom of the test file tells the test program to
 stop reading.