Slide puzzle game in java

// 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
 

URL Searching using java

import java.awt.BorderLayout;
import java.awt.Cursor;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.JSeparator;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableModel;

// The Search Web Crawler
public class SearchCrawler extends JFrame {
  // Max URLs drop-down values.
  private static final String[] MAX_URLS = { "50", "100", "500", "1000" };

  // Cache of robot disallow lists.
  private HashMap disallowListCache = new HashMap();

  // Search GUI controls.
  private JTextField startTextField;

  private JComboBox maxComboBox;

  private JCheckBox limitCheckBox;

  private JTextField logTextField;

  private JTextField searchTextField;

  private JCheckBox caseCheckBox;

  private JButton searchButton;

  // Search stats GUI controls.
  private JLabel crawlingLabel2;

  private JLabel crawledLabel2;

  private JLabel toCrawlLabel2;

  private JProgressBar progressBar;

  private JLabel matchesLabel2;

  // Table listing search matches.
  private JTable table;

  // Flag for whether or not crawling is underway.
  private boolean crawling;

  // Matches log file print writer.
  private PrintWriter logFileWriter;

  // Constructor for Search Web Crawler.
  public SearchCrawler() {
    // Set application title.
    setTitle("Search Crawler");

    // Set window size.
    setSize(600, 600);

    // Handle window closing events.
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        actionExit();
      }
    });

    // Set up File menu.
    JMenuBar menuBar = new JMenuBar();
    JMenu fileMenu = new JMenu("File");
    fileMenu.setMnemonic(KeyEvent.VK_F);
    JMenuItem fileExitMenuItem = new JMenuItem("Exit", KeyEvent.VK_X);
    fileExitMenuItem.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        actionExit();
      }
    });
    fileMenu.add(fileExitMenuItem);
    menuBar.add(fileMenu);
    setJMenuBar(menuBar);

    // Set up search panel.
    JPanel searchPanel = new JPanel();
    GridBagConstraints constraints;
    GridBagLayout layout = new GridBagLayout();
    searchPanel.setLayout(layout);

    JLabel startLabel = new JLabel("Start URL:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(startLabel, constraints);
    searchPanel.add(startLabel);

    startTextField = new JTextField();
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(startTextField, constraints);
    searchPanel.add(startTextField);

    JLabel maxLabel = new JLabel("Max URLs to Crawl:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(maxLabel, constraints);
    searchPanel.add(maxLabel);

    maxComboBox = new JComboBox(MAX_URLS);
    maxComboBox.setEditable(true);
    constraints = new GridBagConstraints();
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(maxComboBox, constraints);
    searchPanel.add(maxComboBox);

    limitCheckBox = new JCheckBox("Limit crawling to Start URL site");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.WEST;
    constraints.insets = new Insets(0, 10, 0, 0);
    layout.setConstraints(limitCheckBox, constraints);
    searchPanel.add(limitCheckBox);

    JLabel blankLabel = new JLabel();
    constraints = new GridBagConstraints();
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    layout.setConstraints(blankLabel, constraints);
    searchPanel.add(blankLabel);

    JLabel logLabel = new JLabel("Matches Log File:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(logLabel, constraints);
    searchPanel.add(logLabel);

    String file = System.getProperty("user.dir")
        + System.getProperty("file.separator") + "crawler.log";
    logTextField = new JTextField(file);
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(logTextField, constraints);
    searchPanel.add(logTextField);

    JLabel searchLabel = new JLabel("Search String:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(searchLabel, constraints);
    searchPanel.add(searchLabel);

    searchTextField = new JTextField();
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.insets = new Insets(5, 5, 0, 0);
    constraints.gridwidth = 2;
    constraints.weightx = 1.0d;
    layout.setConstraints(searchTextField, constraints);
    searchPanel.add(searchTextField);

    caseCheckBox = new JCheckBox("Case Sensitive");
    constraints = new GridBagConstraints();
    constraints.insets = new Insets(5, 5, 0, 5);
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    layout.setConstraints(caseCheckBox, constraints);
    searchPanel.add(caseCheckBox);

    searchButton = new JButton("Search");
    searchButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        actionSearch();
      }
    });
    constraints = new GridBagConstraints();
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 5, 5);
    layout.setConstraints(searchButton, constraints);
    searchPanel.add(searchButton);

    JSeparator separator = new JSeparator();
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 5, 5);
    layout.setConstraints(separator, constraints);
    searchPanel.add(separator);

    JLabel crawlingLabel1 = new JLabel("Crawling:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(crawlingLabel1, constraints);
    searchPanel.add(crawlingLabel1);

    crawlingLabel2 = new JLabel();
    crawlingLabel2.setFont(crawlingLabel2.getFont().deriveFont(Font.PLAIN));
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(crawlingLabel2, constraints);
    searchPanel.add(crawlingLabel2);

    JLabel crawledLabel1 = new JLabel("Crawled URLs:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(crawledLabel1, constraints);
    searchPanel.add(crawledLabel1);

    crawledLabel2 = new JLabel();
    crawledLabel2.setFont(crawledLabel2.getFont().deriveFont(Font.PLAIN));
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(crawledLabel2, constraints);
    searchPanel.add(crawledLabel2);

    JLabel toCrawlLabel1 = new JLabel("URLs to Crawl:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(toCrawlLabel1, constraints);
    searchPanel.add(toCrawlLabel1);

    toCrawlLabel2 = new JLabel();
    toCrawlLabel2.setFont(toCrawlLabel2.getFont().deriveFont(Font.PLAIN));
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(toCrawlLabel2, constraints);
    searchPanel.add(toCrawlLabel2);

    JLabel progressLabel = new JLabel("Crawling Progress:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 0, 0);
    layout.setConstraints(progressLabel, constraints);
    searchPanel.add(progressLabel);

    progressBar = new JProgressBar();
    progressBar.setMinimum(0);
    progressBar.setStringPainted(true);
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 0, 5);
    layout.setConstraints(progressBar, constraints);
    searchPanel.add(progressBar);

    JLabel matchesLabel1 = new JLabel("Search Matches:");
    constraints = new GridBagConstraints();
    constraints.anchor = GridBagConstraints.EAST;
    constraints.insets = new Insets(5, 5, 10, 0);
    layout.setConstraints(matchesLabel1, constraints);
    searchPanel.add(matchesLabel1);
    matchesLabel2 = new JLabel();
    matchesLabel2.setFont(matchesLabel2.getFont().deriveFont(Font.PLAIN));
    constraints = new GridBagConstraints();
    constraints.fill = GridBagConstraints.HORIZONTAL;
    constraints.gridwidth = GridBagConstraints.REMAINDER;
    constraints.insets = new Insets(5, 5, 10, 5);
    layout.setConstraints(matchesLabel2, constraints);
    searchPanel.add(matchesLabel2);

    // Set up matches table.
    table = new JTable(new DefaultTableModel(new Object[][] {},
        new String[] { "URL" }) {
      public boolean isCellEditable(int row, int column) {
        return false;
      }
    });

    // Set up Matches panel.
    JPanel matchesPanel = new JPanel();
    matchesPanel.setBorder(BorderFactory.createTitledBorder("Matches"));
    matchesPanel.setLayout(new BorderLayout());
    matchesPanel.add(new JScrollPane(table), BorderLayout.CENTER);

    // Add panels to display.
    getContentPane().setLayout(new BorderLayout());
    getContentPane().add(searchPanel, BorderLayout.NORTH);
    getContentPane().add(matchesPanel, BorderLayout.CENTER);
  }

  // Exit this program.
  private void actionExit() {
    System.exit(0);
  }

  // Handle Search/Stop button being clicked.
  private void actionSearch() {
    // If stop button clicked, turn crawling flag off.
    if (crawling) {
      crawling = false;
      return;
    }

    ArrayList errorList = new ArrayList();

    // Validate that start URL has been entered.
    String startUrl = startTextField.getText().trim();
    if (startUrl.length() < 1) {
      errorList.add("Missing Start URL.");
    }
    // Verify start URL.
    else if (verifyUrl(startUrl) == null) {
      errorList.add("Invalid Start URL.");
    }

    // Validate that Max URLs is either empty or is a number.
    int maxUrls = 0;
    String max = ((String) maxComboBox.getSelectedItem()).trim();
    if (max.length() > 0) {
      try {
        maxUrls = Integer.parseInt(max);
      } catch (NumberFormatException e) {
      }
      if (maxUrls < 1) {
        errorList.add("Invalid Max URLs value.");
      }
    }

    // Validate that matches log file has been entered.
    String logFile = logTextField.getText().trim();
    if (logFile.length() < 1) {
      errorList.add("Missing Matches Log File.");
    }

    // Validate that search string has been entered.
    String searchString = searchTextField.getText().trim();
    if (searchString.length() < 1) {
      errorList.add("Missing Search String.");
    }

    // Show errors, if any, and return.
    if (errorList.size() > 0) {
      StringBuffer message = new StringBuffer();

      // Concatenate errors into single message.
      for (int i = 0; i < errorList.size(); i++) {
        message.append(errorList.get(i));
        if (i + 1 < errorList.size()) {
          message.append("\n");
        }
      }

      showError(message.toString());
      return;
    }

    // Remove "www" from start URL if present.
    startUrl = removeWwwFromUrl(startUrl);

    // Start the Search Crawler.
    search(logFile, startUrl, maxUrls, searchString);
  }

  private void search(final String logFile, final String startUrl,
      final int maxUrls, final String searchString) {
    // Start the search in a new thread.
    Thread thread = new Thread(new Runnable() {
      public void run() {
        // Show hour glass cursor while crawling is under way.
        setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));

        // Disable search controls.
        startTextField.setEnabled(false);
        maxComboBox.setEnabled(false);
        limitCheckBox.setEnabled(false);
        logTextField.setEnabled(false);
        searchTextField.setEnabled(false);
        caseCheckBox.setEnabled(false);

        // Switch Search button to "Stop."
        searchButton.setText("Stop");

        // Reset stats.
        table.setModel(new DefaultTableModel(new Object[][] {},
            new String[] { "URL" }) {
          public boolean isCellEditable(int row, int column) {
            return false;
          }
        });
        updateStats(startUrl, 0, 0, maxUrls);

        // Open matches log file.
        try {
          logFileWriter = new PrintWriter(new FileWriter(logFile));
        } catch (Exception e) {
          showError("Unable to open matches log file.");
          return;
        }

        // Turn crawling flag on.
        crawling = true;

        // Perform the actual crawling.
        crawl(startUrl, maxUrls, limitCheckBox.isSelected(),
            searchString, caseCheckBox.isSelected());

        // Turn crawling flag off.
        crawling = false;

        // Close matches log file.
        try {
          logFileWriter.close();
        } catch (Exception e) {
          showError("Unable to close matches log file.");
        }

        // Mark search as done.
        crawlingLabel2.setText("Done");

        // Enable search controls.
        startTextField.setEnabled(true);
        maxComboBox.setEnabled(true);
        limitCheckBox.setEnabled(true);
        logTextField.setEnabled(true);
        searchTextField.setEnabled(true);
        caseCheckBox.setEnabled(true);

        // Switch search button back to "Search."
        searchButton.setText("Search");

        // Return to default cursor.
        setCursor(Cursor.getDefaultCursor());

        // Show message if search string not found.
        if (table.getRowCount() == 0) {
          JOptionPane
              .showMessageDialog(
                  SearchCrawler.this,
                  "Your Search String was not found. Please try another.",
                  "Search String Not Found",
                  JOptionPane.WARNING_MESSAGE);
        }
      }
    });
    thread.start();
  }

  // Show dialog box with error message.
  private void showError(String message) {
    JOptionPane.showMessageDialog(this, message, "Error",
        JOptionPane.ERROR_MESSAGE);
  }

  // Update crawling stats.
  private void updateStats(String crawling, int crawled, int toCrawl,
      int maxUrls) {
    crawlingLabel2.setText(crawling);
    crawledLabel2.setText("" + crawled);
    toCrawlLabel2.setText("" + toCrawl);

    // Update progress bar.
    if (maxUrls == -1) {
      progressBar.setMaximum(crawled + toCrawl);
    } else {
      progressBar.setMaximum(maxUrls);
    }
    progressBar.setValue(crawled);

    matchesLabel2.setText("" + table.getRowCount());
  }

  // Add match to matches table and log file.
  private void addMatch(String url) {
    // Add URL to matches table.
    DefaultTableModel model = (DefaultTableModel) table.getModel();
    model.addRow(new Object[] { url });

    // Add URL to matches log file.
    try {
      logFileWriter.println(url);
    } catch (Exception e) {
      showError("Unable to log match.");
    }
  }

  // Verify URL format.
  private URL verifyUrl(String url) {
    // Only allow HTTP URLs.
    if (!url.toLowerCase().startsWith("http://"))
      return null;

    // Verify format of URL.
    URL verifiedUrl = null;
    try {
      verifiedUrl = new URL(url);
    } catch (Exception e) {
      return null;
    }

    return verifiedUrl;
  }

  // Check if robot is allowed to access the given URL.
  private boolean isRobotAllowed(URL urlToCheck) {
    String host = urlToCheck.getHost().toLowerCase();

    // Retrieve host's disallow list from cache.
    ArrayList disallowList = (ArrayList) disallowListCache.get(host);

    // If list is not in the cache, download and cache it.
    if (disallowList == null) {
      disallowList = new ArrayList();

      try {
        URL robotsFileUrl = new URL("http://" + host + "/robots.txt");

        // Open connection to robot file URL for reading.
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(robotsFileUrl.openStream()));

        // Read robot file, creating list of disallowed paths.
        String line;
        while ((line = reader.readLine()) != null) {
          if (line.indexOf("Disallow:") == 0) {
            String disallowPath = line.substring("Disallow:"
                .length());

            // Check disallow path for comments and remove if
            // present.
            int commentIndex = disallowPath.indexOf("#");
            if (commentIndex != -1) {
              disallowPath = disallowPath.substring(0,
                  commentIndex);
            }

            // Remove leading or trailing spaces from disallow path.
            disallowPath = disallowPath.trim();

            // Add disallow path to list.
            disallowList.add(disallowPath);
          }
        }

        // Add new disallow list to cache.
        disallowListCache.put(host, disallowList);
      } catch (Exception e) {
        /*
         * Assume robot is allowed since an exception is thrown if the
         * robot file doesn't exist.
         */
        return true;
      }
    }

    /*
     * Loop through disallow list to see if crawling is allowed for the
     * given URL.
     */
    String file = urlToCheck.getFile();
    for (int i = 0; i < disallowList.size(); i++) {
      String disallow = (String) disallowList.get(i);
      if (file.startsWith(disallow)) {
        return false;
      }
    }

    return true;
  }

  // Download page at given URL.
  private String downloadPage(URL pageUrl) {
    try {
      // Open connection to URL for reading.
      BufferedReader reader = new BufferedReader(new InputStreamReader(
          pageUrl.openStream()));

      // Read page into buffer.
      String line;
      StringBuffer pageBuffer = new StringBuffer();
      while ((line = reader.readLine()) != null) {
        pageBuffer.append(line);
      }

      return pageBuffer.toString();
    } catch (Exception e) {
    }

    return null;
  }

  // Remove leading "www" from a URL's host if present.
  private String removeWwwFromUrl(String url) {
    int index = url.indexOf("://www.");
    if (index != -1) {
      return url.substring(0, index + 3) + url.substring(index + 7);
    }

    return (url);
  }

  // Parse through page contents and retrieve links.
  private ArrayList retrieveLinks(URL pageUrl, String pageContents,
      HashSet crawledList, boolean limitHost) {
    // Compile link matching pattern.
    Pattern p = Pattern.compile("<a\\s+href\\s*=\\s*\"?(.*?)[\" |>]",
        Pattern.CASE_INSENSITIVE);
    Matcher m = p.matcher(pageContents);

    // Create list of link matches.
    ArrayList linkList = new ArrayList();
    while (m.find()) {
      String link = m.group(1).trim();

      // Skip empty links.
      if (link.length() < 1) {
        continue;
      }

      // Skip links that are just page anchors.
      if (link.charAt(0) == '#') {
        continue;
      }

      // Skip mailto links.
      if (link.indexOf("mailto:") != -1) {
        continue;
      }

      // Skip JavaScript links.
      if (link.toLowerCase().indexOf("javascript") != -1) {
        continue;
      }

      // Prefix absolute and relative URLs if necessary.
      if (link.indexOf("://") == -1) {
        // Handle absolute URLs.
        if (link.charAt(0) == '/') {
          link = "http://" + pageUrl.getHost() + link;
          // Handle relative URLs.
        } else {
          String file = pageUrl.getFile();
          if (file.indexOf('/') == -1) {
            link = "http://" + pageUrl.getHost() + "/" + link;
          } else {
            String path = file.substring(0,
                file.lastIndexOf('/') + 1);
            link = "http://" + pageUrl.getHost() + path + link;
          }
        }
      }

      // Remove anchors from link.
      int index = link.indexOf('#');
      if (index != -1) {
        link = link.substring(0, index);
      }

      // Remove leading "www" from URL's host if present.
      link = removeWwwFromUrl(link);

      // Verify link and skip if invalid.
      URL verifiedLink = verifyUrl(link);
      if (verifiedLink == null) {
        continue;
      }

      /*
       * If specified, limit links to those having the same host as the
       * start URL.
       */
      if (limitHost
          && !pageUrl.getHost().toLowerCase().equals(
              verifiedLink.getHost().toLowerCase())) {
        continue;
      }

      // Skip link if it has already been crawled.
      if (crawledList.contains(link)) {
        continue;
      }

      // Add link to list.
      linkList.add(link);
    }

    return (linkList);
  }

  /*
   * Determine whether or not search string is matched in the given page
   * contents.
   */
  private boolean searchStringMatches(String pageContents,
      String searchString, boolean caseSensitive) {
    String searchContents = pageContents;

    /*
     * If case-sensitive search, lowercase page contents for comparison.
     */
    if (!caseSensitive) {
      searchContents = pageContents.toLowerCase();
    }
    // Split search string into individual terms.
    Pattern p = Pattern.compile("[\\s]+");
    String[] terms = p.split(searchString);

    // Check to see if each term matches.
    for (int i = 0; i < terms.length; i++) {
      if (caseSensitive) {
        if (searchContents.indexOf(terms[i]) == -1) {
          return false;
        }
      } else {
        if (searchContents.indexOf(terms[i].toLowerCase()) == -1) {
          return false;
        }
      }
    }

    return true;
  }

  // Perform the actual crawling, searching for the search string.
  public void crawl(String startUrl, int maxUrls, boolean limitHost,
      String searchString, boolean caseSensitive) {
    // Set up crawl lists.
    HashSet crawledList = new HashSet();
    LinkedHashSet toCrawlList = new LinkedHashSet();

    // Add start URL to the to crawl list.
    toCrawlList.add(startUrl);

    /*
     * Perform actual crawling by looping through the To Crawl list.
     */
    while (crawling && toCrawlList.size() > 0) {
      /*
       * Check to see if the max URL count has been reached, if it was
       * specified.
       */
      if (maxUrls != -1) {
        if (crawledList.size() == maxUrls) {
          break;
        }
      }

      // Get URL at bottom of the list.
      String url = (String) toCrawlList.iterator().next();

      // Remove URL from the To Crawl list.
      toCrawlList.remove(url);

      // Convert string url to URL object.
      URL verifiedUrl = verifyUrl(url);

      // Skip URL if robots are not allowed to access it.
      if (!isRobotAllowed(verifiedUrl)) {
        continue;
      }

      // Update crawling stats.
      updateStats(url, crawledList.size(), toCrawlList.size(), maxUrls);

      // Add page to the crawled list.
      crawledList.add(url);

      // Download the page at the given URL.
      String pageContents = downloadPage(verifiedUrl);

      /*
       * If the page was downloaded successfully, retrieve all its links
       * and then see if it contains the search string.
       */
      if (pageContents != null && pageContents.length() > 0) {
        // Retrieve list of valid links from page.
        ArrayList links = retrieveLinks(verifiedUrl, pageContents,
            crawledList, limitHost);

        // Add links to the To Crawl list.
        toCrawlList.addAll(links);

        /*
         * Check if search string is present in page, and if so, record
         * a match.
         */
        if (searchStringMatches(pageContents, searchString,
            caseSensitive)) {
          addMatch(url);
        }
      }

      // Update crawling stats.
      updateStats(url, crawledList.size(), toCrawlList.size(), maxUrls);
    }
  }

  // Run the Search Crawler.
  public static void main(String[] args) {
    SearchCrawler crawler = new SearchCrawler();
    crawler.show();
  }
}
/**
A quantifier determines how many times an expression is matched. The quantifiers are shown here:
+   Match one or more.
*   Match zero or more.
?   Match zero or one.

*/

/*
Character Sequence Explanation

<a Look for the characters "<a".

\\s+ Look for one or more space characters.

href Look for the characters "href".

\\s* Look for zero or more space characters.

=    Look for the character "--".

\\s* Look for zero or more space characters.

\"?  Look for zero or one quote character.

(.*?)Look for zero or more of any character until the next part of the pattern is matched, and place the results in a group.

[\">]Look for quote character or greater than (">") character.

*/
 

Message Digest SHA-1 and MD5 in JAVA

import java.awt.Container;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.swing.ButtonGroup;
import javax.swing.JCheckBox;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class MessageDigestTest {
  public static void main(String[] args) {
    JFrame f = new MessageDigestFrame();
    f.show();
  }
}

class MessageDigestFrame extends JFrame {
  public MessageDigestFrame() {
    setTitle("MessageDigestTest");
    setSize(400, 200);
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });

    JPanel panel = new JPanel();
    ButtonGroup group = new ButtonGroup();
    ActionListener listener = new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        JCheckBox b = (JCheckBox) event.getSource();
        setAlgorithm(b.getText());
      }
    };
    addCheckBox(panel, "SHA-1", group, true, listener);
    addCheckBox(panel, "MD5", group, false, listener);

    Container contentPane = getContentPane();

    contentPane.add(panel, "North");
    contentPane.add(new JScrollPane(message), "Center");
    contentPane.add(digest, "South");
    digest.setFont(new Font("Monospaced", Font.PLAIN, 12));

    setAlgorithm("SHA-1");

    JMenuBar menuBar = new JMenuBar();
    JMenu menu = new JMenu("File");
    JMenuItem fileDigestItem = new JMenuItem("File digest");
    fileDigestItem.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        loadFile();
      }
    });
    menu.add(fileDigestItem);
    JMenuItem textDigestItem = new JMenuItem("Text area digest");
    textDigestItem.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        String m = message.getText();
        computeDigest(m.getBytes());
      }
    });
    menu.add(textDigestItem);
    menuBar.add(menu);
    setJMenuBar(menuBar);
  }

  public void addCheckBox(Container c, String name, ButtonGroup g,
      boolean selected, ActionListener listener) {
    JCheckBox b = new JCheckBox(name, selected);
    c.add(b);
    g.add(b);
    b.addActionListener(listener);
  }

  public void setAlgorithm(String alg) {
    try {
      currentAlgorithm = MessageDigest.getInstance(alg);
      digest.setText("");
    } catch (NoSuchAlgorithmException e) {
      digest.setText("" + e);
    }
  }

  public void loadFile() {
    JFileChooser chooser = new JFileChooser();
    chooser.setCurrentDirectory(new File("."));

    int r = chooser.showOpenDialog(this);
    if (r == JFileChooser.APPROVE_OPTION) {
      String name = chooser.getSelectedFile().getAbsolutePath();
      computeDigest(loadBytes(name));
    }
  }

  public byte[] loadBytes(String name) {
    FileInputStream in = null;

    try {
      in = new FileInputStream(name);
      ByteArrayOutputStream buffer = new ByteArrayOutputStream();
      int ch;
      while ((ch = in.read()) != -1)
        buffer.write(ch);
      return buffer.toByteArray();
    } catch (IOException e) {
      if (in != null) {
        try {
          in.close();
        } catch (IOException e2) {
        }
      }
      return null;
    }
  }

  public void computeDigest(byte[] b) {
    currentAlgorithm.reset();
    currentAlgorithm.update(b);
    byte[] hash = currentAlgorithm.digest();
    String d = "";
    for (int i = 0; i < hash.length; i++) {
      int v = hash[i] & 0xFF;
      if (v < 16)
        d += "0";
      d += Integer.toString(v, 16).toUpperCase() + " ";
    }
    digest.setText(d);
  }

  private JTextArea message = new JTextArea();

  private JTextField digest = new JTextField();

  private MessageDigest currentAlgorithm;
}

Bitwise Operators in Java

public class BitwiseOperators {
   public BitwiseOperators( ) {
  int a = 11; //1 0 1 1
  int b = 12; //1 1 0 0

      System.out.println("a & b : "+(a & b));
      System.out.println("a | b : "+(a | b));
      System.out.println("a ^ b : "+(a ^ b));
      System.out.println("~a : "+(~a));
      System.out.println("a << b : "+(a << b));
      System.out.println("a >> b : "+(a >> b));
      System.out.println("a >>> b : "+(a >>> b));
        }
   public static void main(String args[]){
       new BitwiseOperators();
   }
}

Runtime Polymorphism or method overriding

class A{
    public void fun1(int x){
        System.out.println(""int in Class A is : " + x : " + x);
        }
    }
    class B extends A{
        public void fun1(int x){
            System.out.println("int in Class B is : " + x);
            }
        }
        public class polytwo{
            public static void main(String[] args){
                A obj;
                obj=new A(); // line 1
                obj.fun1(2);  // line 2 (prints ""int in Class A is : 2")
                obj=new B();  // line 3
                obj.fun1(5);  // line 4 (prints "int in Class A is : 5")
                }
        }
int in class A is: 2
int in class B is:5

Compline time Polymorpism or method overloading

class A{
    public void fun1(int x){
        System.out.println("The value of class A is : " + x);
    }
    public void fun1(int x,int y){
        System.out.println("The value of class B is : "+x +" and "+ y);
    }
}
public class polyone{
    public static void main(String[] args){
        A obj=new A();
        // Here compiler decides that fun1(int) is to be called and "int" will be printed.
        obj.fun1(2);
        // Here compiler decides that fun1(int,int) is to be called and "int and int" will be printed.
        obj.fun1(2,3);
    }
}

output

The value of class A is: 2
The value of class B is: 2 and 3

inheritance in java

class A{
    public void fun1(int x){
        System.out.println("Int in A is :" + x);
        }
    }
class B extends A{
    public void fun2(int x,int y){
        fun1(6);  // prints "int in A"
        System.out.println("Int in B is :" + x + " and " + y);
        }
    }
public class inherit{
    public static void main(String[] args){
        B obj=new B();
        obj.fun2(2, 5);
        }
}

output
Int in A is: 6
Int in B is: 2 and 5

Encapsulation Example in java

class Check{
    private int amount=0;
    public int getAmount(){
        return amount;
    }
    public void setAmount(int amt){
        amount=amt;
    }
}
public class Mainclass{
    public static void main(String[] args){
        int amt=0;
        Check obj=new Check();
        obj.setAmount(200);
        amt=obj.getAmount();
        System.out.println("Your current amount is :"+amt);
        }
}

output
Your current amount is: 200

Calculate Circle Area using Java

/*
 Calculate Circle Area using Java Example
 This Calculate Circle Area using Java Example shows how to calculate 
 area of circle using it's radius.
*/

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalculateCircleAreaExample {

public static void main(String[] args) {

int radius = 0;
System.out.println("Please enter radius of a circle");

try
{
//get the radius from console
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
radius = Integer.parseInt(br.readLine());
}
//if invalid value was entered
catch(NumberFormatException ne)
{
System.out.println("Invalid radius value" + ne);
System.exit(0);
}
catch(IOException ioe)
{
System.out.println("IO Error :" + ioe);
System.exit(0);
}

/*
   * Area of a circle is
   * pi * r * r
   * where r is a radius of a circle.
   */

//NOTE : use Math.PI constant to get value of pi
double area = Math.PI * radius * radius;

System.out.println("Area of a circle is " + area);
}
}

/*
Output of Calculate Circle Area using Java Example would be
Please enter radius of a circle
19
Area of a circle is 1134.1149479459152
*/