Java: Example - Slide Puzzle

// SlidePuzzle.java - Puzzle to slide pieces to correct position.
// Fred Swartz, 2003-May, 2004-May
//   The SlidePuzzle program consists of three files:
//   SlidePuzzle.java      - this file with main to create window.
//   SlidePuzzleGUI.java   - implements the GUI interface.
//   SlidePuzzleModel.java - the logical functioning.

import javax.swing.JFrame;

///////////////////////////////////////////// class SlidePuzzle
class SlidePuzzle {
    //============================================= method main
    public static void main(String[] args) {
        JFrame window = new JFrame("Slide Puzzle");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setContentPane(new SlidePuzzleGUI());
        window.pack();  // finalize layout
        window.show();  // make window visible
        window.setResizable(false);
    }//end main
}//endclass SlidePuzzle

// SlidePuzzleGUI.java - GUI for SlidePuzzle
// Fred Swartz, 2003-May-10, 2004-May-3
//
// The SlidePuzzleGUI class creates a panel which 
//     contains two subpanels.
//     1. In the north is a subpanel for controls (just a button now).
//     2. In the center a graphics
// This needs a few improvements.  
//   Both the GUI and Model define the number or rows and columns.
//          How would you set both from one place? 

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

/////////////////////////////////////////////////// class SlidePuzzleGUI
// This class contains all the parts of the GUI interface
class SlidePuzzleGUI extends JPanel {
    //=============================================== instance variables
    private GraphicsPanel    _puzzleGraphics;
    private SlidePuzzleModel _puzzleModel = new SlidePuzzleModel();
    //end instance variables


    //====================================================== constructor
    public SlidePuzzleGUI() {
        //--- Create a button.  Add a listener to it.
        JButton newGameButton = new JButton("New Game");
        newGameButton.addActionListener(new NewGameAction());

        //--- Create control panel
        JPanel controlPanel = new JPanel();
        controlPanel.setLayout(new FlowLayout());
        controlPanel.add(newGameButton);
        
        //--- Create graphics panel
        _puzzleGraphics = new GraphicsPanel();
        
        //--- Set the layout and add the components
        this.setLayout(new BorderLayout());
        this.add(controlPanel, BorderLayout.NORTH);
        this.add(_puzzleGraphics, BorderLayout.CENTER);
    }//end constructor


    //////////////////////////////////////////////// class GraphicsPanel
    // This is defined inside the outer class so that
    // it can use the outer class instance variables.
    class GraphicsPanel extends JPanel implements MouseListener {
        private static final int ROWS = 3;
        private static final int COLS = 3;
        
        private static final int CELL_SIZE = 80; // Pixels
        private Font _biggerFont;
        
        
        //================================================== constructor
        public GraphicsPanel() {
            _biggerFont = new Font("SansSerif", Font.BOLD, CELL_SIZE/2);
            this.setPreferredSize(
                   new Dimension(CELL_SIZE * COLS, CELL_SIZE*ROWS));
            this.setBackground(Color.black);
            this.addMouseListener(this);  // Listen own mouse events.
        }//end constructor
        
        
        //=======================================x method paintComponent
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (int r=0; r<ROWS; r++) {
                for (int c=0; c<COLS; c++) {
                    int x = c * CELL_SIZE;
                    int y = r * CELL_SIZE;
                    String text = _puzzleModel.getFace(r, c);
                    if (text != null) {
                        g.setColor(Color.gray);
                        g.fillRect(x+2, y+2, CELL_SIZE-4, CELL_SIZE-4);
                        g.setColor(Color.black);
                        g.setFont(_biggerFont);
                        g.drawString(text, x+20, y+(3*CELL_SIZE)/4);
                    }
                }
            }
        }//end paintComponent
        
        
        //======================================== listener mousePressed
        public void mousePressed(MouseEvent e) {
            //--- map x,y coordinates into a row and col.
            int col = e.getX()/CELL_SIZE;
            int row = e.getY()/CELL_SIZE;
            
            if (!_puzzleModel.moveTile(row, col)) {
                // moveTile moves tile if legal, else returns false.
                Toolkit.getDefaultToolkit().beep();
            }
            
            this.repaint();  // Show any updates to model.
        }//end mousePressed
        
        
        //========================================== ignore these events
        public void mouseClicked (MouseEvent e) {}
        public void mouseReleased(MouseEvent e) {}
        public void mouseEntered (MouseEvent e) {}
        public void mouseExited  (MouseEvent e) {}
    }//end class GraphicsPanel
    
    ////////////////////////////////////////// inner class NewGameAction
    public class NewGameAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            _puzzleModel.reset();
            _puzzleGraphics.repaint();
        }
    }//end inner class NewGameAction

}//end class SlidePuzzleGUI

// SlidePuzzleModel.java - Slide pieces to correct position.
// Fred Swartz, 2003-May-10

/////////////////////////////////////////// class SlidePuzzleModel
class SlidePuzzleModel {
    private static final int ROWS = 3;
    private static final int COLS = 3;
    
    private Tile[][] _contents;  // All tiles.
    private Tile     _emptyTile; // The empty space.
    
    
    //================================================= constructor
    public SlidePuzzleModel() {
        _contents = new Tile[ROWS][COLS];
        reset();               // Initialize and shuffle tiles.
    }//end constructor
    
    
    //===================================================== getFace
    // Return the string to display at given row, col.
    String getFace(int row, int col) {
        return _contents[row][col].getFace();
    }//end getFace
    
    
    //======================================================= reset
    // Initialize and shuffle the tiles.
    public void reset() {
        for (int r=0; r<ROWS; r++) {
            for (int c=0; c<COLS; c++) {
                _contents[r][c] = new Tile(r, c, "" + (r*COLS+c+1));
            }
        }
        //--- Set last tile face to null to mark empty space
        _emptyTile = _contents[ROWS-1][COLS-1];
        _emptyTile.setFace(null);
        
        //-- Shuffle - Exchange each tile with random tile.
        for (int r=0; r<ROWS; r++) {
            for (int c=0; c<COLS; c++) {
                exchangeTiles(r, c, (int)(Math.random()*ROWS)
                                  , (int)(Math.random()*COLS));
            }
        }
    }//end reset
    
    
    //==================================================== moveTile
    // Move a tile to empty position beside it, if possible.
    // Return true if it was moved, false if not legal.
    public boolean moveTile(int r, int c) {
        //--- It's a legal move if the empty cell is next to it.
        return checkEmpty(r, c, -1, 0) || checkEmpty(r, c, 1, 0)
            || checkEmpty(r, c, 0, -1) || checkEmpty(r, c, 0, 1);
    }//end moveTile
    
    
    //================================================== checkEmpty
    // Check to see if there is an empty position beside tile.
    // Return true and exchange if possible, else return false.
    private boolean checkEmpty(int r, int c, int rdelta, int cdelta) {
        int rNeighbor = r + rdelta;
        int cNeighbor = c + cdelta;
        //--- Check to see if this neighbor is on board and is empty.
        if (isLegalRowCol(rNeighbor, cNeighbor) 
                  && _contents[rNeighbor][cNeighbor] == _emptyTile) {
            exchangeTiles(r, c, rNeighbor, cNeighbor);
            return true;
        }
        return false;
    }//end checkEmpty
    
    
    //=============================================== isLegalRowCol
    // Check for legal row, col
    public boolean isLegalRowCol(int r, int c) {
        return r>=0 && r<ROWS && c>=0 && c<COLS;
    }//end isLegalRowCol
    
    
    //=============================================== exchangeTiles
    // Exchange two tiles.
    private void exchangeTiles(int r1, int c1, int r2, int c2) {
        Tile temp = _contents[r1][c1];
        _contents[r1][c1] = _contents[r2][c2];
        _contents[r2][c2] = temp;
    }//end exchangeTiles
        
    
    //=================================================== isGameOver
    public boolean isGameOver() {
        for (int r=0; r<ROWS; r++) {
            for (int c=0; c<ROWS; c++) {
                Tile trc = _contents[r][c];
                return trc.isInFinalPosition(r, c);
            }
        }
        
        //--- Falling thru loop means nothing out of place.
        return true;
    }//end isGameOver
}//end class SlidePuzzleModel
    
    
    
////////////////////////////////////////////////////////// class Tile
// Represents the individual "tiles" that slide in puzzle.
class Tile {
    //============================================ instance variables
    private int _row;     // row of final position
    private int _col;     // col of final position
    private String _face;  // string to display 
    //end instance variables
    
    
    //==================================================== constructor
    public Tile(int row, int col, String face) {
        _row = row;
        _col = col;
        _face = face;
    }//end constructor
    
    
    //======================================================== setFace
    public void setFace(String newFace) {
        _face = newFace;
    }//end getFace
    
    
    //======================================================== getFace
    public String getFace() {
        return _face;
    }//end getFace
   
   
    //=============================================== isInFinalPosition
    public boolean isInFinalPosition(int r, int c) {
        return r==_row && c==_col;
    }//end isInFinalPosition
}//end class Tile