Ошибка головоломки судоку, то есть не отвечает

package sudoku;
import java.awt.*;
import java.awt.Event.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;
public class SudokuGame extends JFrame {
	//Name constant for game properties
public static final int grid_size=9;
public static int subgrid_size =3;

//constant for ui controls(sizes and ccontrol 
	public static final  int Cell_size=60;  //cell width
	public static final int canvas_width = Cell_size* grid_size;
	public static final int canvas_height = Cell_size*grid_size;
	
	public static final Color open_cell_bgcolor = Color.YELLOW;
	public static final Color open_cell_Text_yes = new Color(0,255,0);
	public static final Color  open_cell_no = Color.RED;
	public static final Color closed_cell_bgcolor= new Color(240,240, 240);
	public static final Color closed_cell_Text = Color.BLACK;
	public static final Font Font_Numbers = new Font("Monospaced",Font.BOLD , 20);
	int row,col;
	//private int countFilled;
	//private boolean ColumnHasNumber[][] = new boolean[9][9];
	//private boolean RowHasNumber[][];
	//private boolean LineHasNumber[] = new boolean[][][];
	//private boolean Block3x3HasNumber[][][];
	InputListener listner =new InputListener();
	//game board contains 9*9 Jtextfields 
	private JTextField [][] tf_cells = new JTextField[grid_size][grid_size];
	int count;
	JTextField emptyCells = new JTextField();
	
	private int[][] puzzle = 
		{{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},
     	{3,4,5,2,8,6,1,7,9}};
	
	private boolean masks[][] = {
		{false,false,false,false,true,true,true,false,true},
		{false,false,false,true,false,false,false,false,true},
		{true,false,false,true,false,false,false,false,false},
		{false,false,false,true,true,false,true,false,false},
		{false,false,true,false,false,true,false,true,false},
		{false,true,false,true,false,true,true,false,false},
		{false,false,false,false,true,false,false,false,false},
		{false,false,true,true,false,false,false,false,false},
		{false,false,true,true,false,true,false,false,true}};
	
		public SudokuGame()
		{
			Container cp = getContentPane();
			cp.setLayout(new GridLayout(grid_size,grid_size));
			for(int row = 0; row<grid_size;++row)
			{
				for(int col=0;col<grid_size;++col)
				{
					tf_cells[row][col] = new JTextField();
					cp.add(tf_cells[row][col]);
					if(masks[row][col])
					{
						tf_cells[row][col].setText("");
						tf_cells[row][col].setEditable(true);
						tf_cells[row][col].setBackground(open_cell_bgcolor);
					}
					else
					{
						tf_cells[row][col].setText(puzzle[row][col]+"");
						tf_cells[row][col].setEditable(false);
						tf_cells[row][col].setBackground(closed_cell_bgcolor);
						tf_cells[row][col].setForeground(closed_cell_Text);
					}
					
					tf_cells[row][col].setHorizontalAlignment(JTextField.CENTER);
					tf_cells[row][col].setFont(Font_Numbers);
					
					
				}
			}
			cp.setPreferredSize(new Dimension(canvas_width,canvas_width));
			pack();
			setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			setTitle("Sudoku");
			setVisible(true);
			
			
		}
		
		private class InputListener implements ActionListener
		{
			@Override
			public void actionPerformed(ActionEvent e)
			{
				int Row_selected = -1;
				int column_selected =-1;
				JTextField source = (JTextField)e.getSource();
				boolean found=false;
				for( row=0;row<grid_size&&!found;++row)
				{
					for(col=0;col<grid_size&&!found;++col){
						if(tf_cells[row][col]==source)
						{
							Row_selected = row;
							column_selected= col;
							found = false;
						}
					}
						 
				}
				String x = tf_cells[Row_selected][column_selected].getText();
				 int y = Integer.parseInt(x);
				 if(y==puzzle[Row_selected][column_selected])
				 {
					 tf_cells[Row_selected][column_selected].setBackground(Color.GREEN);
					 
				 }
				 else
				 {
					 tf_cells[Row_selected][column_selected].setBackground(Color.RED);
					 
				 }
				
			}
			//
		}
			
			
		
		
		
		
		
     	
		
		
		
			

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		SudokuGame sg = new SudokuGame();
		
		try
		{
			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
			
		}
		catch (Exception e) {
			e.printStackTrace();
			// TODO: handle exception
		}
		

	}

}