Sudoku (Java Edition) - RunUI

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

public class RunUI extends JFrame implements ActionListener, MouseListener, KeyListener, ChangeListener {

  private int w, h;

  private Board board;
  private Board solvedBoard;

  private Color permColor = Color.blue;
  private Color backColor = new Color(238, 238, 238);

  private Font baseFont = new Font("Serif", Font.BOLD, 50);
  private Font solveFont = new Font("Serif", Font.PLAIN, 50);

  private JLabel[][] boardLabels;
  private JButton startButton, solveButton, resetButton, checkButton;
  private JPanel panel;
  private JFrame frame;

  private JSlider difficultySlider;
  private JTextField difficultyBox;

  public RunUI() {
    super("Sudoku");
    initializeGUI();
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    repaint();
  }

  public void repaint(Board b) {
    for (int y = 0; y < 9; y++) {
      for (int x = 0; x < 9; x++) {
        //System.out.println(perms[x][y]);
        if (!b.getPerm(x, y)) {
          boardLabels[x][y].setFont(baseFont);
          boardLabels[x][y].setForeground(Color.black);
          boardLabels[x][y].setBackground(backColor);
        } else {
          boardLabels[x][y].setFont(solveFont);
          boardLabels[x][y].setForeground(permColor);
          boardLabels[x][y].setBackground(Color.yellow);
        }
        if (b.getValue(x, y) > 0) {
          boardLabels[x][y].setText("" + b.getValue(x, y));
        } else {
          boardLabels[x][y].setText(" ");
        }
      }
    }

    pack();
    panel.requestFocus();
    panel.repaint();
  }

  public void repaint() {
    pack();
    panel.requestFocus();
    panel.repaint();
  }

  private void setBoard(Board b) {
    board = b;
    board.solve();
    solvedBoard = new Board(b);
    board.reset();
  }

  public void checkSolved() {
    boolean complete = true;
    for (int y = 0; y < 9; y++) {
      for (int x = 0; x < 9; x++) {
        if (board.getValue(x, y) == 0) {
          complete = false;
        }
      }
    }
    if (complete) {
      if (board.validate()) {
        permColor = Color.green;
      } else {
        permColor = Color.red;
      }
    } else {
      permColor = Color.blue;
    }
  }

  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == startButton) {
      setBoard(new Board());
      resetButton.setEnabled(true);
      //if (difficultySlider.getValue() <= 3) {
        solveButton.setEnabled(true);
      //}
      board.puzzle(difficultySlider.getValue());
      repaint(board);
    } else if (e.getSource() == solveButton) {
      board = new Board(solvedBoard, board.getPerms());
      checkSolved();
      repaint(board);
    } else if (e.getSource() == resetButton) {
      board.reset();
      repaint(board);
    } else if (e.getSource() == difficultyBox) {
      difficultySlider.setValue(Integer.parseInt(difficultyBox.getText()));
    }
  }

  public void stateChanged(ChangeEvent e) {
    if (e.getSource() == difficultySlider) {
      difficultyBox.setText("" + difficultySlider.getValue());
      /*if (difficultySlider.getValue() > 3) {
        solveButton.setEnabled(false);
      } else if (board != null) {
        solveButton.setEnabled(true);
      }*/
      repaint();
    }
  }

  public void mousePressed(MouseEvent e) {
  }

  public void mouseReleased(MouseEvent e) {
  }

  public void mouseEntered(MouseEvent e) {
    JLabel source = (JLabel)e.getSource();
    source.setOpaque(true);
    //System.out.println("entered");
    repaint();
  }

  public void mouseExited(MouseEvent e) {
    JLabel source = (JLabel)e.getSource();
    //System.out.println("exited");
    source.setOpaque(false);
    repaint();
  }

  public void mouseClicked(MouseEvent e) {
  }

  public void keyTyped(KeyEvent e) {
    //System.out.println("Key pressed!");
    if (e.getID() == KeyEvent.KEY_TYPED && board != null) {
      char c = e.getKeyChar();
      int i = Character.getNumericValue(c);
      //System.out.println(i);
      if (c == '\b') {
        for (int y = 0; y < 9; y++) {
          for (int x = 0; x < 9; x++) {
            if (boardLabels[x][y].isOpaque() && board.getPerm(x, y)) {
              board.setValue(x, y, 0);
              checkSolved();
              repaint(board);
            }
          }
        }
      } else if (i >= 1 && i <= 9) {
        for (int y = 0; y < 9; y++) {
          for (int x = 0; x < 9; x++) {
            if (boardLabels[x][y].isOpaque() && board.getPerm(x, y)) {
              board.setValue(x, y, i);
              checkSolved();
              repaint(board);
            }
          }
        }
      }
    }
  }

  public void keyPressed(KeyEvent e) {
  }

  public void keyReleased(KeyEvent e) {
  }


  public void initializeGUI() {
    int offsetX = 62;
    int offsetY = 62;

    panel = new JPanel() {
      public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setStroke(new BasicStroke(4));
        int big = 192;
        int small = 63;
        for (int i = 0; i < 9; i++) {
          g2.drawRect(offsetX-2+big*(i%3), offsetY-2+big*(i/3), big, big);
        }
        g2.setStroke(new BasicStroke(1));
        for (int y = 0; y < 9; y++) {
          for (int x = 0; x < 9; x++) {
            g2.drawRect(offsetX-1+small*x+3*(x/3), offsetY-1+small*y+3*(y/3), small, small);
          }
        }
      }
    };

    panel.addKeyListener(this);

    this.setSize(new Dimension(700, 700));
    panel.setLayout(null);
    panel.setPreferredSize(new Dimension(700, 700));

    boardLabels = new JLabel[9][9];
    Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
    if (w == 0 && h == 0) {
      w = (int)screen.getWidth();
      h = (int)screen.getHeight();
    }
    //System.out.println(w + ":" + h);

    startButton = new JButton("Generate");
    startButton.addActionListener(this);
    panel.add(startButton);
    startButton.setBounds(10, 10, 100, 30);

    solveButton = new JButton("Solve");
    solveButton.addActionListener(this);
    panel.add(solveButton);
    solveButton.setBounds(110, 10, 100, 30);
    solveButton.setEnabled(false);

    resetButton = new JButton("Reset");
    resetButton.addActionListener(this);
    panel.add(resetButton);
    resetButton.setBounds(210, 10, 100, 30);
    resetButton.setEnabled(false);

    difficultySlider = new JSlider(JSlider.VERTICAL, 1, 5, 3);
    panel.add(difficultySlider);
    difficultySlider.addChangeListener(this);
    difficultySlider.setBounds(10, 75, 30, 150);
    difficultySlider.setMajorTickSpacing(2);
    difficultySlider.setMinorTickSpacing(1);
    difficultySlider.setPaintTicks(true);
    //difficultySlider.setPaintLabels(true);

    difficultyBox = new JTextField("3");
    panel.add(difficultyBox);
    difficultyBox.addActionListener(this);
    difficultyBox.setBounds(16, 50, 16, 20);

    for (int y = 0; y < 9; y++) {
      for (int x = 0; x < 9; x++) {
        boardLabels[x][y] = new JLabel("", SwingConstants.CENTER);
        panel.add(boardLabels[x][y]);
        //boardLabels[x][y].setFocusable(true);
        boardLabels[x][y].addMouseListener(this);
        //boardLabels[x][y].addKeyListener(this);
        int cellSize = 62;
        boardLabels[x][y].setBounds(offsetX+cellSize*x+3*(x/3)+x, offsetY+cellSize*y+3*(y/3)+y, cellSize, cellSize);
      }
    }
    pack();
    getContentPane().add(panel);
    getRootPane().setDefaultButton(startButton);
    panel.setVisible(true);

  }

  public void init() {
    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        setVisible(true);
      }
    });
  }

}