Sudoku Program

Question

Write a Sudoku validator for 4x4 grids made up of 2x2 regions instead of 9x9 grids made up of 3x3 regions. Sudoku puzzles that use 4x4 grids only use the numerical digits 1 through 4 instead of 1 through 9.
Things to Remember:
-Dont use arrays
-Input 16 values into 16 seperate variables
-Try using only if and if/else statements
Outcome should look something like this:
Welcome to the Sudoku Checker v1.0!
This program checks simple, small, 4x4 Sudoku grids for correctness. Each column, row and 2x2 region contains the numbers 1 through 4 only once.
To check your Sudoku, enter your board one row at a time, with each digit separated by a space. Hit ENTER at the end of a row.
Enter Row 1: 1 2 3 4
Enter Row 2: 3 4 2 1
Enter Row 3: 1 2 3 4
Enter Row 4: 4 3 2 1
Thank you. Now checking ...
REG-1:GOOD
REG-2:GOOD
REG-3:GOOD
REG-4:GOOD
ROW-1:GOOD
ROW-2:GOOD
ROW-3:GOOD
ROW-4:GOOD
COL-1:BAD
COL-2:BAD
COL-3:GOOD
COL-4:GOOD
SUDO:INVALID

Answer 1

I built a generic sudoku solver which not only validates, but suggests moves /solves an n x m (dimensions can be different and arbitrary) board by using an int[m][n] array for entered value and a Set<Integer>[m][n] for the possibilities. I added a method called runRules() and created rules off of the following two abstract classes.
package tjacobs.games.sudoku;
Remove possible values on cell row,col using the entered values in the board
public abstract class AbstractCellRule {
     public abstract void runCellRule(SudokuBoard sudoku, int[][] board, int row, int col);
package tjacobs.games.sudoku;
import java.awt.Rectangle;
For rules dealing with a range (row, column, box) in general, not focused on 1 particular cell
public abstract class AbstractRangeRule {
     public abstract void runRangeRule(SudokuBoard sudoku, int[][] board, Rectangle bounds);
}