Create a sudoku solver in java .

package test;

public class Sudoku {

	private final int BLOCK_SIZE = 3;

	private final int ROW_SIZE = BLOCK_SIZE * BLOCK_SIZE;

	private int nrOfSolutions, nrOfTests;

	private int[][] board;

	private int[][][] testBoard = {
			/* |---------|---------|---------| */
			{ { 5, 3, 0, 0, 7, 0, 0, 0, 0 }, { 6, 0, 0, 1, 9, 5, 0, 0, 0 }, { 0, 9, 8, 0, 0, 0, 0, 6, 0 },
					/* |---------|---------|---------| */
					{ 8, 0, 0, 0, 6, 0, 0, 0, 3 }, { 4, 0, 0, 8, 0, 3, 0, 0, 1 }, { 7, 0, 0, 0, 2, 0, 0, 0, 6 },
					/* |---------|---------|---------| */
					{ 0, 6, 0, 0, 0, 0, 2, 8, 0 }, { 0, 0, 0, 4, 1, 9, 0, 0, 5 }, { 0, 0, 0, 0, 8, 0, 0, 7, 9 } },
			/* |---------|---------|---------| */

			/* |---------|---------|---------| */
			{ { 5, 3, 4, 6, 7, 8, 9, 1, 2 }, { 6, 7, 2, 1, 9, 5, 3, 4, 8 }, { 1, 9, 8, 3, 4, 2, 5, 6, 7 },
					/* |---------|---------|---------| */
					{ 8, 5, 9, 7, 6, 1, 4, 2, 3 }, { 4, 2, 6, 8, 5, 3, 7, 9, 1 }, { 7, 1, 3, 9, 2, 4, 8, 5, 6 },
					/* |---------|---------|---------| */
					{ 9, 6, 1, 5, 3, 7, 2, 8, 4 }, { 2, 8, 7, 4, 1, 9, 6, 3, 5 }, { 3, 4, 5, 2, 8, 6, 1, 7, 0 } },
			/* |---------|---------|---------| */

			/* |---------|---------|---------| */
			{ { 0, 0, 0, 5, 4, 2, 0, 0, 0 }, { 9, 6, 7, 0, 0, 0, 0, 0, 0 }, { 0, 0, 0, 0, 0, 0, 3, 1, 8 },
					/* |---------|---------|---------| */
					{ 0, 0, 0, 0, 7, 0, 8, 6, 4 }, { 0, 2, 0, 6, 0, 4, 0, 9, 0 }, { 6, 4, 5, 0, 1, 0, 0, 0, 0 },
					/* |---------|---------|---------| */
					{ 8, 9, 1, 0, 0, 0, 0, 0, 0 }, { 0, 0, 0, 0, 0, 0, 5, 4, 7 }, { 0, 0, 0, 3, 2, 6, 0, 0, 0 } },
			/* |---------|---------|---------| */

	};

	public void testSudokuSolver() {
		for (int[][] s : this.testBoard) {
			this.board = s;
			this.print();

			nrOfSolutions = 0;
			nrOfTests = 0;
			this.solve(0, 0);
		}
	}

	private boolean isBlockOk(int row, int col, int num) {
		
		int iRowStart = (row / BLOCK_SIZE) * BLOCK_SIZE;
		int iColStart = (col / BLOCK_SIZE) * BLOCK_SIZE;

		for ( int irow = iRowStart; irow < iRowStart + BLOCK_SIZE; irow++) {
			for ( int icol = iColStart; icol < iColStart + BLOCK_SIZE; icol++) {

				if (num == board[irow][icol]) {
					return false;
				}
			}
		}
		return true;
	}

	private boolean isRowOk(int row, int num) {
		for (int i = 0; i < ROW_SIZE; i++) {
			if (num == board[row][i]) {
				return false;
			}
		}
		return true;
	}

	private boolean isColOK(int col, int num) {
		for (int i = 0; i < ROW_SIZE; i++) {
			if (num == board[i][col]) {
				return false;
			}
		}
		return true;
	}

	public void print() {
		final String horizBorder = " ┼────────┼────────┼────────┼";

		System.out.println();

		for (int i = 0; i < ROW_SIZE; i++) {
			if (0 == i % 3) {
				System.out.println(horizBorder);
			}

			for (int j = 0; j < ROW_SIZE; j++) {
				if (0 == j % 3) {
					System.out.print(" │ ");
				}

				int num = board[i][j];
				if (num == 0) {
					System.out.print("_ ");
				} else {
					System.out.print(num + " ");
				}

			}
			System.out.println(" │");
		}
		System.out.println(horizBorder);
	}

	private boolean isValid(int num, int row, int col) {
		return (isBlockOk(row, col, num) && isColOK(col, num) && isRowOk(row, num));
	}

	public boolean solve(int row, int col) {

		for (int i = 1; i < BLOCK_SIZE; i++) {
			for (int j = 1; j < BLOCK_SIZE; j++) {
				if (board[i][j] == 0) {
					for (int k = 1; k <= 9; k++) {
						board[i][j] = k;
						if (isValid(i, j, k) && solve(i, col)) {
							return true;
						}
						board[i][j] = 0;
					}
					return false;
				}
			}
		}
		return true;
	}

	public static void main(String[] args) {
		new Sudoku().testSudokuSolver();
	}

}