Gomoku.java

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

/**
 * This panel lets two users play Go Moku (a.k.a Pente) against each 
 * other.  Black always starts the game.  When a player gets five-in-a-row,
 * that player wins.  The game ends in a draw if the board is filled
 * before either player wins.
 *
 * The class has a main() routine that lets it be run as a stand-alone
 * application.  The application just opens a window that uses an object
 * of type GoMoku as its content pane.
 * 
 */

public class GoMoku extends JPanel {
   
   /**
    * Main routine makes it possible to run GoMoku as a stand-alone
    * application.  Opens a window showing a GoMoku panel; the program
    * ends when the user closes the window.
    */
   public static void main(String[] args) {
      JFrame window = new JFrame("GoMoku");
      GoMoku content = new GoMoku();
      window.setContentPane(content);
      window.pack();
      Dimension screensize = Toolkit.getDefaultToolkit().getScreenSize();
      window.setLocation( (screensize.width - window.getWidth())/2,
            (screensize.height - window.getHeight())/2 );
      window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      window.setResizable(false);  
      window.setVisible(true);
   }
   

   private JButton newGameButton;  // Button for starting a new game.

   private JButton resignButton;   // Button that a player can use to end the 
                                   //   game by resigning.
   
   private JLabel message;  // Label for displaying messages to the user.
   
   
   /**
    *  The constructor lays out the panel.  The work of
    *  the game is all done in the Board object.  A null layout
    *  is used, and all setup of sizes and positions is done here.
    */
   public GoMoku() {
      
      setLayout(null);  // I will do the layout myself.
      
      setPreferredSize( new Dimension(350,250) );
      
      setBackground(new Color(0,150,0));  // Dark green background.
      
      /* Create the components and add them to the panel. */
      
      Board board = new Board();  // Note: The constructor for the
                                  //   board also creates the buttons
                                  //   and label.
      add(board);
      add(newGameButton);
      add(resignButton);
      add(message);
      
      /* Set the position and size of each component by calling
         its setBounds() method. */
      
      board.setBounds(16,16,172,172); // Note:  size MUST be 172-by-172 !
      newGameButton.setBounds(210, 60, 120, 30);
      resignButton.setBounds(210, 120, 120, 30);
      message.setBounds(0, 200, 350, 30);
   }
   
   
   // ----------------------- Nested class -----------------------------------
   
   /**
    * This panel displays a 168-by-168 pixel checkerboard pattern with
    * a 2-pixel black border.  It is assumed that the size of the
    * canvas is set to exactly 172-by-172 pixels.  This class does
    * the work of letting the users play Go Moku, and it displays
    * the checkerboard.  In this program, the board has 13 rows and
    * columns of squares.
    */
   class Board extends JPanel implements ActionListener, MouseListener {
      
      int[][] board;   // The data for the board is kept here.  The values
                      //   in this array are chosen from the following constants.
      
      static final int EMPTY = 0,       // Represents an empty square.
                       WHITE = 1,       // A white piece.
                       BLACK = 2;       // A black piece.
      
      boolean gameInProgress; // Is a game currently in progress?
      
      int currentPlayer;      // Whose turn is it now?  The possible values
                              //    are WHITE and BLACK.  (This is valid only while
                              //    a game is in progress.)
      
      int win_r1, win_c1, win_r2, win_c2;  // When a player wins by getting five or more
                                           // pieces in a row, the squares at the
                                           // ends of the row are (win_r1,win_c1)
                                           // and (win_r2,win_c2).  A red line is
                                           // drawn between these squares.  When there
                                           // are not five pieces in a row, the value of
                                           // win_r1 is -1.  The values are set in the
                                           // count() method.  The value of win_r1 is
                                           // tested in the paintComponent() method.
      
      /**
       * Constructor.  Create the buttons and label.  Listen for mouse
       * clicks and for clicks on the buttons.  Create the board and
       * start the first game.
       */
      public Board() {
         setBackground(Color.LIGHT_GRAY);
         addMouseListener(this);
         resignButton = new JButton("Resign");
         resignButton.addActionListener(this);
         newGameButton = new JButton("New Game");
         newGameButton.addActionListener(this);
         message = new JLabel("",JLabel.CENTER);
         message.setFont(new  Font("Serif", Font.BOLD, 14));
         message.setForeground(Color.GREEN);
         board = new int[13][13];
         doNewGame();
      }
      

      /**
       * Respond to user's click on one of the two buttons.
       */
      public void actionPerformed(ActionEvent evt) {
         Object src = evt.getSource();
         if (src == newGameButton)
            doNewGame();
         else if (src == resignButton)
            doResign();
      }
      
      
      /**
       * Begin a new game; this is called by the actionPerformed()
       * method when a user clicks the New Game button.
       */
      void doNewGame() {
         if (gameInProgress == true) {
               // This should not be possible because New Game button
               // is enabled only when it is legal to use it, but it doesn't 
               // hurt to check.
            message.setText("Finish the current game first!");
            return;
         }
         for (int row = 0; row < 13; row++)       // Fill the board with EMPTYs
            for (int col = 0; col < 13; col++)
               board[row][col] = EMPTY;
         currentPlayer = BLACK;   // BLACK moves first.
         message.setText("BLACK:  Make your move.");
         gameInProgress = true;
         newGameButton.setEnabled(false);
         resignButton.setEnabled(true);
         win_r1 = -1;  // This value indicates that no red line is to be drawn.
         repaint();
      }
      
      
      /**
       * Current player resigns; this is called by the actionPerformed()
       * method when a user clicks the Resign button.  Game ends, and
       * opponent wins.
       */
      void doResign() {
         if (gameInProgress == false) {
                // This should not be possible.
            message.setText("There is no game in progress!");
            return;
         }
         if (currentPlayer == WHITE)
            message.setText("WHITE resigns.  BLACK wins.");
         else
            message.setText("BLACK resigns.  WHITE wins.");
         newGameButton.setEnabled(true);
         resignButton.setEnabled(false);
         gameInProgress = false;
      }
      
      
      /**
       * This method is called whenever the game ends.  The parameter, str,
       * is displayed as a message, and the buttons are enabled/disabled
       * to reflect the fact that a game is not currently in progress.
       */
      void gameOver(String str) {
         message.setText(str);
         newGameButton.setEnabled(true);
         resignButton.setEnabled(false);
         gameInProgress = false;
      }
      
      
      /**
       * This is called by mousePressed() when a player clicks on the
       * square in the specified row and col.  It has already been checked
       * that a game is, in fact, in progress.
       */
      void doClickSquare(int row, int col) {
         
         /* Check that the user clicked an empty square.  If not, show an
          error message and exit. */
         
         if ( board[row][col] != EMPTY ) {
            if (currentPlayer == BLACK)
               message.setText("BLACK:  Please click an empty square.");
            else
               message.setText("WHITE:  Please click an empty square.");
            return;
         }
         
         /* Make the move.  Check if the board is full or if the move
          is a winning move.  If so, the game ends.  If not, then it's
          the other user's turn. */
         
         board[row][col] = currentPlayer;  // Make the move.
         repaint();
         
         if (winner(row,col)) {  // First, check for a winner.
            if (currentPlayer == WHITE)
               gameOver("WHITE wins the game!");
            else
               gameOver("BLACK wins the game!");
            return;
         }
         
         boolean emptySpace = false;     // Check if the board is full.
         for (int i = 0; i < 13; i++)
            for (int j = 0; j < 13; j++)
               if (board[i][j] == EMPTY)
                  emptySpace = true;
         if (emptySpace == false) {
            gameOver("The game ends in a draw.");
            return;
         }
         
         /* Continue the game.  It's the other player's turn. */
         
         if (currentPlayer == BLACK) {
            currentPlayer = WHITE;
            message.setText("WHITE:  Make your move.");
         }
         else {  
            currentPlayer = BLACK;
            message.setText("BLACK:  Make your move.");
         }
         
      }  // end doClickSquare()
      
      
      /**
       * This is called just after a piece has been played on the
       * square in the specified row and column.  It determines
       * whether that was a winning move by counting the number
       * of squares in a line in each of the four possible
       * directions from (row,col).  If there are 5 squares (or more)
       * in a row in any direction, then the game is won.
       */
      private boolean winner(int row, int col) {
         
         if (count( board[row][col], row, col, 1, 0 ) >= 5)
            return true;
         if (count( board[row][col], row, col, 0, 1 ) >= 5)
            return true;
         if (count( board[row][col], row, col, 1, -1 ) >= 5)
            return true;
         if (count( board[row][col], row, col, 1, 1 ) >= 5)
            return true;
         
         /* When we get to this point, we know that the game is not
          won.  The value of win_r1, which was changed in the count()
          method, has to be reset to -1, to avoid drawing a red line
          on the board. */
         
         win_r1 = -1;
         return false;
         
      }  // end winner()
      
      
      /**
       * Counts the number of the specified player's pieces starting at
       * square (row,col) and extending along the direction specified by
       * (dirX,dirY).  It is assumed that the player has a piece at
       * (row,col).  This method looks at the squares (row + dirX, col + dirY),
       * (row + 2*dirX, col + 2*dirY), ... until it hits a square that is
       * off the board or is not occupied by one of the player's pieces.
       * It counts the squares that are occupied by the player's pieces.
       * Furthermore, it sets (win_r1,win_c1) to mark last position where
       * it saw one of the player's pieces.  Then, it looks in the
       * opposite direction, at squares (row - dirX, col-dirY),
       * (row - 2*dirX, col - 2*dirY), ... and does the same thing.
       * Except, this time it sets (win_r2,win_c2) to mark the last piece.
       * Note:  The values of dirX and dirY must be 0, 1, or -1.  At least
       * one of them must be non-zero.
       */
      private int count(int player, int row, int col, int dirX, int dirY) {
         
         int ct = 1;  // Number of pieces in a row belonging to the player.
         
         int r, c;    // A row and column to be examined
         
         r = row + dirX;  // Look at square in specified direction.
         c = col + dirY;
         while ( r >= 0 && r < 13 && c >= 0 && c < 13 && board[r][c] == player ) {
            // Square is on the board and contains one of the players's pieces.
            ct++;
            r += dirX;  // Go on to next square in this direction.
            c += dirY;
         }
         
         win_r1 = r - dirX;  // The next-to-last square looked at.
         win_c1 = c - dirY;  //    (The LAST one looked at was off the board or
         //    did not contain one of the player's pieces.
         
         r = row - dirX;  // Look in the opposite direction.
         c = col - dirY;
         while ( r >= 0 && r < 13 && c >= 0 && c < 13 && board[r][c] == player ) {
            // Square is on the board and contains one of the players's pieces.
            ct++;
            r -= dirX;   // Go on to next square in this direction.
            c -= dirY;
         }
         
         win_r2 = r + dirX;
         win_c2 = c + dirY;
         
         // At this point, (win_r1,win_c1) and (win_r2,win_c2) mark the endpoints
         // of the line of pieces belonging to the player.
         
         return ct;
         
      }  // end count()
      
      
      /**
       * Draws the board and the pieces on the board.  If the game has
       * been won by getting five or more pieces in a row, draws a red line
       * through the pieces.
       */
      public void paintComponent(Graphics g) {
         
         super.paintComponent(g); // Fill with background color, lightGray
         
         /* Draw a two-pixel black border around the edges of the canvas,
          and draw grid lines in darkGray.  */
         
         g.setColor(Color.DARK_GRAY);
         for (int i = 1; i < 13; i++) {
            g.drawLine(1 + 13*i, 0, 1 + 13*i, getSize().height);
            g.drawLine(0, 1 + 13*i, getSize().width, 1 + 13*i);
         }
         g.setColor(Color.BLACK);
         g.drawRect(0,0,getSize().width-1,getSize().height-1);
         g.drawRect(1,1,getSize().width-3,getSize().height-3);
         
         /* Draw the pieces that are on the board. */
         
         for (int row = 0; row < 13; row++)
            for (int col = 0; col < 13; col++)
               if (board[row][col] != EMPTY)
                  drawPiece(g, board[row][col], row, col);
         
         /* If the game has been won, then win_r1 >= 0.  Draw a line to mark
          the five (or more) winning pieces. */
         
         if (win_r1 >= 0)
            drawWinLine(g);
         
      }  // end paintComponent()
      
      
      /**
       * Draw a piece in the square at (row,col).  The color is specified
       * by the piece parameter, which should be either BLACK or WHITE.
       */
      private void drawPiece(Graphics g, int piece, int row, int col) {
         if (piece == WHITE)
            g.setColor(Color.WHITE);
         else
            g.setColor(Color.BLACK);
         g.fillOval(3 + 13*col, 3 + 13*row, 10, 10);
      }
      
      
      /**
       * Draw a 2-pixel wide red line from the middle of the square at
       * (win_r1,win_c1) to the middle of the square at (win_r2,win_c2).
       * This routine is called to mark the pieces that won the game.
       * The values of the variables are set in the count() method.
       */
      private void drawWinLine(Graphics g) {
         g.setColor(Color.RED);
         g.drawLine( 8 + 13*win_c1, 8 + 13*win_r1, 8 + 13*win_c2, 8 + 13*win_r2 );
         if (win_r1 == win_r2)
            g.drawLine( 8 + 13*win_c1, 7 + 13*win_r1, 8 + 13*win_c2, 7 + 13*win_r2 );
         else
            g.drawLine( 7 + 13*win_c1, 8 + 13*win_r1, 7 + 13*win_c2, 8 + 13*win_r2 );
      }
      
      
      /**
       * Respond to a user click on the board.  If no game is
       * in progress, show an error message.  Otherwise, find
       * the row and column that the user clicked and call
       * doClickSquare() to handle it.
       */
      public void mousePressed(MouseEvent evt) {
         if (gameInProgress == false)
            message.setText("Click \"New Game\" to start a new game.");
         else {
            int col = (evt.getX() - 2) / 13;
            int row = (evt.getY() - 2) / 13;
            if (col >= 0 && col < 13 && row >= 0 && row < 13)
               doClickSquare(row,col);
         }
      }
      
      
      public void mouseReleased(MouseEvent evt) { }
      public void mouseClicked(MouseEvent evt) { }
      public void mouseEntered(MouseEvent evt) { }
      public void mouseExited(MouseEvent evt) { }
      
      
   }  // end nested class Board
   
   
   
} // end class GoMoku