#################
NestedLayout.java Layout of complicated GUI by taking advantage of nested containers. Uses WindowUtilities.java and ExitListener.java. 
##################
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;

/** An example demonstrating the use of nested containers
 *  to lay out the components. See GridBagTest.java for
 *  implementation by a single layout manager, GridBagLayout.
 *
 *******************
 */

public class NestedLayout extends JPanel {

  private JTextArea textArea;
  private JButton bSaveAs, bOk, bExit;
  private JTextField fileField;

  public NestedLayout() {

    setLayout(new BorderLayout(2,2));
    setBorder(BorderFactory.createEtchedBorder());

    textArea = new JTextArea(12,40);  // 12 rows, 40 cols
    bSaveAs = new JButton("Save As");
    fileField = new JTextField("C:\\Document.txt");
    bOk = new JButton("OK");
    bExit = new JButton("Exit");

    add(textArea,BorderLayout.CENTER);

    // Set up buttons and textfield in bottom panel.
    JPanel bottomPanel = new JPanel();
    bottomPanel.setLayout(new GridLayout(2,1));

    JPanel subPanel1 = new JPanel();
    JPanel subPanel2 = new JPanel();
    subPanel1.setLayout(new BorderLayout());
    subPanel2.setLayout(new FlowLayout(FlowLayout.RIGHT,2,2));

    subPanel1.add(bSaveAs,BorderLayout.WEST);
    subPanel1.add(fileField,BorderLayout.CENTER);
    subPanel2.add(bOk);
    subPanel2.add(bExit);

    bottomPanel.add(subPanel1);
    bottomPanel.add(subPanel2);

    add(bottomPanel,BorderLayout.SOUTH);
  }

  public static void main(String[] args) {
    WindowUtilities.setNativeLookAndFeel();
    JFrame frame = new JFrame("Nested Containers");
    frame.setContentPane(new NestedLayout());
    frame.addWindowListener(new ExitListener());
    frame.pack();
    frame.setVisible(true);
  }
}
##########################

#######################
# CardDemo.java A demo providing multiple buttons to select a playing card. A Panel, using CardLayout control which of four possible subpanels, holding a different card, to display.Uses the following class and images:
    * CardPanel.java A Panel that displays a playing card.
    * ImageLabel.java A Canvas for displaying images.
    * Ace.gif, King.gif, Queen.gif, Jack.gif.
#####################
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

/** An example of CardLayout. The right side of the window holds
 *  a Panel that uses CardLayout to control four possible
 *  subpanels (each of which is a CardPanel that shows a
 *  picture of a playing card). The buttons on the left side
 *  of the window manipulate the "cards" in this layout by
 *  calling methods in the right-hand panel's layout manager.
 *
 *********************************

public class CardDemo extends Applet implements ActionListener {
  private Button first, last, previous, next;
  private String[] cardLabels = { "Jack","Queen","King","Ace" };
  private CardPanel[] cardPanels = new CardPanel[4];
  private CardLayout layout;
  private Panel cardDisplayPanel;

  public void init() {
    setBackground(Color.white);
    setLayout(new BorderLayout());
    addButtonPanel();
    addCardDisplayPanel();
  }

  private void addButtonPanel() {
    Panel buttonPanel = new Panel();
    buttonPanel.setLayout(new GridLayout(9, 1));
    Font buttonFont = new Font("SansSerif", Font.BOLD, 18);
    buttonPanel.setFont(buttonFont);
    for(int i=0; inot use CardLayout. Rather, instances of CardPanel
 *  are contained in another window used in the CardDemo
 *  example. It is this enclosing window that uses CardLayout
 *  to manipulate which CardPanel it shows.
 *
 *************************

public class CardPanel extends Panel {
  private Label name;
  private ImageLabel picture;

  public CardPanel(String cardName,
                   URL directory, String imageFile) {
    setLayout(new BorderLayout());
    name = new Label(cardName, Label.CENTER);
    name.setFont(new Font("SanSerif", Font.BOLD, 50));
    add(name, BorderLayout.NORTH);
    picture = new ImageLabel(directory, imageFile);
    Panel picturePanel = new Panel();
    picturePanel.add(picture);
    add(picturePanel, BorderLayout.CENTER);
    setSize(getPreferredSize());
  }

  public Label getLabel() {
    return(name);
  }

  public ImageLabel getImageLabel() {
    return(picture);
  }
}
*******************
ImageLabel.java A Canvas for displaying images.
*******************
import java.awt.*;
import java.net.*; 

/** A class for displaying images. It places the Image
 *  into a canvas so that it can moved around by layout
 *  managers, will get repainted automatically, etc.
 *  No mouseXXX or action events are defined, so it is
 *  most similar to the Label Component.
 *  


 *  By default, with FlowLayout the ImageLabel takes
 *  its minimum size (just enclosing the image). The
 *  default with BorderLayout is to expand to fill
 *  the region in width (North/South), height
 *  (East/West) or both (Center). This is the same
 *  behavior as with the builtin Label class. If you
 *  give an explicit setSize or
 *  setBounds call before adding the
 *  ImageLabel to the Container, this size will
 *  override the defaults.
 *  


 *  Here is an example of its use:
 *  


 *  

 *  public class ShowImages extends Applet {
 *    private ImageLabel image1, image2;
 *
 *    public void init() {
 *      image1 = new ImageLabel(getCodeBase(),
 *                              "some-image.gif");
 *      image2 = new ImageLabel(getCodeBase(),
 *                              "other-image.jpg");
 *      add(image1);
 *      add(image2);
 *    }
 *  }
 *  


 *
  */

public class ImageLabel extends Canvas {
  // Instance variables.
  
  // The actual Image drawn on the canvas. 
  private Image image;

  // A String corresponding to the URL of the image you will 
  // get if you call the constructor with no arguments.
  private static String defaultImageString
    = "http://java.sun.com/lib/images/" +
      "logo.java.color-transp.55x60.gif";

  // The URL of the image. But sometimes we will use an existing
  // image object (e.g. made by createImage) for which this info 
  // will not be available, so a default string is used here.
  private String imageString = "";

  // Turn this on to get verbose debugging messages. 
  private boolean debug = false;

  /** Amount of extra space around the image. */
  
  private int border = 0;

  /** If there is a non-zero border, what color should it be? 
   *  Default is to use the background color of the Container.
   */
   
  private Color borderColor = null;
  
  // Width and height of the Canvas. This is the
  //  width/height of the image plus twice the border.
  private int width, height;

  /** Determines if it will be sized automatically. If the user
   *  issues a setSize() or setBounds()call before adding the 
   *  label to the Container, or if the LayoutManager resizes 
   *  before drawing (as with BorderLayout), then those sizes
   *  override the default, which is to make the label the same 
   *  size as the image it holds (after reserving space for the 
   *  border, if any). This flag notes this, so subclasses that
   *  override ImageLabel need to check this flag, and if it is 
   *  true, and they draw modified image, then they need to draw 
   *  them based on the width height variables, not just blindly 
   *  drawing them full size.
   */
   
  private boolean explicitSize = false;
  private int explicitWidth=0, explicitHeight=0;
  
  // The MediaTracker that can tell if image has been loaded 
  // before trying to paint it or setSize based on its size.
  private MediaTracker tracker;
  
  // Used by MediaTracker to be sure image is loaded before 
  // paint & setSize, since you can't find out the size until it
  // is done loading.
  private static int lastTrackerID=0;
  private int currentTrackerID;
  private boolean doneLoading = false;

  private Container parentContainer;

  /** Create an ImageLabel with the default image.
   *
   * @see #getDefaultImageString
   * @see #setDefaultImageString
   */
  // Remember that the funny "this()" syntax calls
  // constructor of same class
  public ImageLabel() {
    this(defaultImageString);
  }
  
  /** Create an ImageLabel using the image at URL
   *  specified by the string.
   *
   * @param imageURLString A String specifying the
   *   URL of the image.
   */
   
  public ImageLabel(String imageURLString) {
    this(makeURL(imageURLString));
  }

  /** Create an ImageLabel using the image at URL
   *  specified.
   *
   * @param imageURL The URL of the image.
   */
   
  public ImageLabel(URL imageURL) {
    this(loadImage(imageURL));
    imageString = imageURL.toExternalForm();
  }

  /** Create an ImageLabel using the image in the file
   *  in the specified directory.
   *
   * @param imageDirectory Directory containing image
   * @param file Filename of image
   */
   
  public ImageLabel(URL imageDirectory, String file) {
    this(makeURL(imageDirectory, file));
    imageString = file;
  }
  
  /** Create an ImageLabel using the image specified. The other
   *  constructors eventually call this one, but you may want 
   *  to call it directly if you already have an image (e.g. 
   *  created through createImage).
   *
   * @param image The image
   */
   
  public ImageLabel(Image image) {
    this.image = image;
    tracker = new MediaTracker(this);
    currentTrackerID = lastTrackerID++;
    tracker.addImage(image, currentTrackerID);
  }

  /** Makes sure that the Image associated with the Canvas is 
   *  done loading before returning, since loadImage spins off
   *  a separate thread to do the loading. Once you get around 
   *  to drawing the image, this will make sure it is loaded,
   *  waiting if not. The user does not need to call this at 
   *  all, but if several ImageLabels are used in the same 
   *  Container, this can cause several repeated layouts, so 
   *  users might want to explicitly call this themselves before
   *  adding the ImageLabel to the Container. Another 
   *  alternative is to start asynchronous loading by calling 
   *  prepareImage on the ImageLabel's image (see getImage). 
   *
   * @param doLayout Determines if the Container should be 
   *   re-laid out after you are finished waiting. This 
   *   should be true when called from user functions, 
   *   but is set to false when called from getPreferredSize 
   *   to avoid an infinite loop. This is needed when using 
   *   BorderLayout, which calls getPreferredSize
   *   before calling paint.
   */
   
  public void waitForImage(boolean doLayout) {
    if (!doneLoading) {
      debug("[waitForImage] - Resizing and waiting for "
            + imageString);
      try { tracker.waitForID(currentTrackerID); } 
      catch (InterruptedException ie) {} 
      catch (Exception e) { 
        System.out.println("Error loading "
                           + imageString + ": "
                           + e.getMessage()); 
        e.printStackTrace(); 
      } 
      if (tracker.isErrorID(0)) 
        new Throwable("Error loading image "
                      + imageString).printStackTrace();
      doneLoading = true;
      if (explicitWidth != 0)
        width = explicitWidth;
      else
        width = image.getWidth(this) + 2*border;
      if (explicitHeight != 0)
        height = explicitHeight;
      else
        height = image.getHeight(this) + 2*border;
      setSize(width, height);
      debug("[waitForImage] - " + imageString + " is "
            + width + "x" + height + ".");

      // If no parent, you are OK, since it will have
      // been resized before being added. But if
      // parent exists, you have already been added,
      // and the change in size requires re-layout. 
      if (((parentContainer = getParent()) != null)
          && doLayout) {
        setBackground(parentContainer.getBackground());
        parentContainer.doLayout();
      }
    }
  }

  /** Moves the image so that it is centered at
   *  the specified location, as opposed to the setLocation
   *  method of Component which places the top left
   *  corner at the specified location.
   *  


   *  Note: The effects of this could be undone
   *  by the LayoutManager of the parent Container, if
   *  it is using one. So this is normally only used
   *  in conjunction with a null LayoutManager.
   *
   * @param x The X coord of center of the image
   *          (in parent's coordinate system)
   * @param y The Y coord of center of the image
   *          (in parent's coordinate system)
   * @see java.awt.Component#setLocation
   */

  public void centerAt(int x, int y) {
    debug("Placing center of " + imageString + " at ("
          + x + "," + y + ")");
    setLocation(x - width/2, y - height/2); 
  }

  /** Determines if the x and y (in the ImageLabel's
   *  own coordinate system) is inside the
   *  ImageLabel. Put here because Netscape 2.02 has
   *  a bug in which it doesn't process contains() and
   *  locate() tests correctly. 
   */
   
  public synchronized boolean contains(int x, int y) {
    return((x >= 0) && (x <= width)
           && (y >= 0) && (y <= height));
  }
  
  /** Draws the image. If you override this in a
   *  subclass, be sure to call super.paint.
   */
   
  public void paint(Graphics g) {
    if (!doneLoading)
      waitForImage(true);
    else {
      if (explicitSize)
        g.drawImage(image, border, border,
                    width-2*border, height-2*border,
                    this);
      else
        g.drawImage(image, border, border, this);
      drawRect(g, 0, 0, width-1, height-1,
               border, borderColor);
    }
  }

  /** Used by layout managers to calculate the usual
   *  size allocated for the Component. Since some
   *  layout managers (e.g. BorderLayout) may
   *  call this before paint is called, you need to
   *  make sure that the image is done loading, which
   *  will force a setSize, which determines the values
   *  returned.
   */
  public Dimension getPreferredSize() {
    if (!doneLoading)
      waitForImage(false);
    return(super.getPreferredSize());
  }

  /** Used by layout managers to calculate the smallest
   *  size allocated for the Component. Since some
   *  layout managers (e.g. BorderLayout) may
   *  call this before paint is called, you need to
   *  make sure that the image is done loading, which
   *  will force a setSize, which determines the values
   *  returned.
   */
   public Dimension getMinimumSize() {
     if (!doneLoading)
       waitForImage(false);
     return(super.getMinimumSize());
   }
  
  // LayoutManagers (such as BorderLayout) might call
  // setSize or setBounds with only 1 dimension of
  // width/height non-zero. In such a case, you still
  // want the other dimension to come from the image
  // itself.

  /** Resizes the ImageLabel. If you don't setSize the
   *  label explicitly, then what happens depends on
   *  the layout manager. With FlowLayout, as with
   *  FlowLayout for Labels, the ImageLabel takes its
   *  minimum size, just enclosing the image. With
   *  BorderLayout, as with BorderLayout for Labels,
   *  the ImageLabel is expanded to fill the
   *  section. Stretching GIF/JPG files does not always
   *  result in clear looking images. So just as
   *  with builtin Labels and Buttons, don't
   *  use FlowLayout if you don't want the Buttons to
   *  get resized. If you don't use any
   *  LayoutManager, then the ImageLabel will also
   *  just fit the image.
   *  


   *  Note that if you setSize explicitly, you must do
   *  it before the ImageLabel is added to the
   *  Container. In such a case, the explicit size
   *  overrides the image dimensions.
   *
   * @see #setBounds
   */
   
  public void setSize(int width, int height) {
    if (!doneLoading) {
      explicitSize=true;
      if (width > 0)
        explicitWidth=width;
      if (height > 0)
        explicitHeight=height;
    }
    super.setSize(width, height);
  }

  /** Resizes the ImageLabel. If you don't setSize the
   *  label explicitly, then what happens depends on
   *  the layout manager. With FlowLayout, as with
   *  FlowLayout for Labels, the ImageLabel takes its
   *  minimum size, just enclosing the image. With
   *  BorderLayout, as with BorderLayout for Labels,
   *  the ImageLabel is expanded to fill the
   *  section. Stretching GIF/JPG files does not always
   *  result in clear looking images. So just as
   *  with builtin Labels and Buttons, don't
   *  use FlowLayout if you don't want the Buttons to
   *  get resized. If you don't use any
   *  LayoutManager, then the ImageLabel will also
   *  just fit the image.
   *  


   *  Note that if you setSize explicitly, you must do
   *  it before the ImageLabel is added to the
   *  Container. In such a case, the explicit size
   *  overrides the image dimensions.
   *
   * @see #setSize
   */
   
  public void setBounds(int x, int y,
                      int width, int height) {
    if (!doneLoading) {
      explicitSize=true;
      if (width > 0)
        explicitWidth=width;
      if (height > 0)
        explicitHeight=height;
    }
    super.setBounds(x, y, width, height);
  }
  
  // You can't just set the background color to
  // the borderColor and skip drawing the border,
  // since it messes up transparent gifs. You
  // need the background color to be the same as
  // the container.
  
  /** Draws a rectangle with the specified OUTSIDE
   *  left, top, width, and height.
   *  Used to draw the border.
   */
   
  protected void drawRect(Graphics g,
                          int left, int top,
                          int width, int height,
                          int lineThickness,
                          Color rectangleColor) {
    g.setColor(rectangleColor);
    for(int i=0; i
                                

# BorderTest.java Five buttons arranged by BorderLayout
BorderLayout divides the window into five regions: NORTH, SOUTH, EAST, WEST, and CENTER. 
/./././././././././././././
import java.applet.Applet;
import java.awt.*;

/** An example of BorderLayout.
 *
 &&&&&&&&&&&&&&&&&&&&&&&&&&&

public class BorderTest extends Applet {
  public void init() {
    setLayout(new BorderLayout());
    add(new Button("Button 1"), BorderLayout.NORTH);
    add(new Button("Button 2"), BorderLayout.SOUTH);
    add(new Button("Button 3"), BorderLayout.EAST);
    add(new Button("Button 4"), BorderLayout.WEST);
    add(new Button("Button 5"), BorderLayout.CENTER);
  }
}
&&&&&&&&&&&&&&&&&&&&

Checkboxes.java Inherits from CloseableFrame.java. 
******************
import java.awt.*;

/./././././././././

public class Checkboxes extends CloseableFrame {
  public static void main(String[] args) {
    new Checkboxes();
  }

  public Checkboxes() {
    super("Checkboxes");
    setFont(new Font("SansSerif", Font.BOLD, 18));
    setLayout(new GridLayout(0, 2));
    Checkbox box;
    for(int i=0; i<12; i++) {
      box = new Checkbox("Checkbox " + i);
      if (i%2 == 0) {
        box.setState(true);
      }
      add(box);
    }
    pack();
    setVisible(true);
  }
}

import java.applet.Applet;
import java.awt.*;

/** Places a Panel holding 100 buttons in a ScrollPane that is
 *  too small to hold it.
 *
  */

public class ScrollPaneTest extends Applet {
  public void init() {
    setLayout(new BorderLayout());
    ScrollPane pane = new ScrollPane();
    Panel bigPanel = new Panel();
    bigPanel.setLayout(new GridLayout(10, 10));
    for(int i=0; i<100; i++) {
      bigPanel.add(new Button("Button " + i));
    }
    pane.add(bigPanel);
    add(pane, BorderLayout.CENTER);
  }
}

FlowTest.java 
*************
FlowTest.java Five buttons arranged by FlowLayout
By default, FlowLayout arranges components in rows, left to right, and centered. 
/././././././././././././
import java.applet.Applet;
import java.awt.*;

/** FlowLayout puts components in rows.
 *
 ************************************
public class FlowTest extends Applet {
  public void init() {
    for(int i=1; i<6; i++) {
      add(new Button("Button " + i));
    }
  }
}

SavedFrame.java
****************
A Frame that lets you draw circles with mouse clicks 
//**************
import java.awt.*;
import java.awt.event.*;
import java.io.*;

/** A Frame that lets you draw circles with mouse clicks 
 *  and then save the Frame and all circles to disk.
 *
public class SavedFrame extends CloseableFrame
                        implements ActionListener {
  
  /** If a saved version exists, use it. Otherwise create a 
   *  new one.
   */
                          
  public static void main(String[] args) {
    SavedFrame frame;
    File serializeFile = new File(serializeFilename);
    if (serializeFile.exists()) {
      try {
        FileInputStream fileIn = 
          new FileInputStream(serializeFile);
        ObjectInputStream in = new ObjectInputStream(fileIn);
        frame = (SavedFrame)in.readObject();
        frame.setVisible(true);
      } catch(IOException ioe) {
        System.out.println("Error reading file: " + ioe);
      } catch(ClassNotFoundException cnfe) {
        System.out.println("No such class: " + cnfe);
      }
    } else {
      frame = new SavedFrame();
    }
  }

  private static String serializeFilename ="SavedFrame.ser";
  private CirclePanel circlePanel;
  private Button clearButton, saveButton;

  /** Build a frame with CirclePanel and buttons. */
                          
  public SavedFrame() {
    super("SavedFrame");
    setBackground(Color.white);
    setFont(new Font("Serif", Font.BOLD, 18));
    circlePanel = new CirclePanel();
    add("Center", circlePanel);
    Panel buttonPanel = new Panel();
    buttonPanel.setBackground(Color.lightGray);
    clearButton = new Button("Clear");
    saveButton = new Button("Save");
    buttonPanel.add(clearButton);
    buttonPanel.add(saveButton);
    add(buttonPanel, BorderLayout.SOUTH);
    clearButton.addActionListener(this);
    saveButton.addActionListener(this);
    setSize(300, 300);
    setVisible(true);
  }

  /** If "Clear" clicked, delete all existing circles. If "Save"
   *  clicked, save existing frame configuration (size, 
   *  location, circles, etc.) to disk.
   */
                          
  public void actionPerformed(ActionEvent event) {
    if (event.getSource() == clearButton) {
      circlePanel.removeAll();
      circlePanel.repaint();
    } else if (event.getSource() == saveButton) {
      try {
        FileOutputStream fileOut =
          new FileOutputStream("SavedFrame.ser");
        ObjectOutputStream out = 
          new ObjectOutputStream(fileOut);
        out.writeObject(this);
        out.flush();
        out.close();
      } catch(IOException ioe) {
        System.out.println("Error saving frame: " + ioe);
      }
    }
  }
}
****************

******************
# FrameExample1.java
******************
import java.awt.*;

/** 
 */

public class FrameExample1 {
  public static void main(String[] args) {
    Frame f = new Frame("Frame Example 1");
    f.setSize(400, 300);
    f.setVisible(true);
  }
}
*********************
# FrameExample2.java 
*********************
import java.awt.*;

/** 
 */

public class FrameExample2 extends Frame {
  public static void main(String[] args) {
    new FrameExample2();
  }
 
  public FrameExample2() {
    super("Frame Example 2");
    setSize(400, 300);
    setVisible(true);
  }
}
**********************

ThreadedRSAKey.java  Illustrates converting a method in an existing class from a single-threaded method to a multi-threaded method. In this example, RSAKey  computes an RSA public-private key pair, where the key size has a specified number of digits. As large prime numbers require considerable CPU time, ThreadedRSAKey converts the original computeKey method in RSAKey  to a multi-threaded method, thus allowing simultaneous (multithreaded) computation of multiple key pairs. Uses the following classes:

import java.io.*;   

 * RSAKey.java Computes RSA public-private key pairs of arbitrary length.


 * Primes.java Generates large prime numbers.


/** An example of creating a background process for an
 *  originally nonthreaded, class method. Normally,
 *  the program flow will wait until computeKey is finished.
 
public class ThreadedRSAKey extends RSAKey implements Runnable {

  // Store strNumDigits into the thread to prevent race
  // conditions.
  public void computeKey(String strNumDigits) {
    RSAThread t = new RSAThread(this, strNumDigits);
    t.start();
  }

  // Retrieve the stored strNumDigits and call the original
  // method.  Processing is now done in the background.
  public void run() {
    RSAThread t = (RSAThread)Thread.currentThread();
    String strNumDigits = t.getStrDigits();
    super.computeKey(strNumDigits);
  }

  public static void main(String[] args){
    ThreadedRSAKey key = new ThreadedRSAKey();
    for (int i=0; i " + n);
    System.out.println("public  => " + encrypt);
    System.out.println("private => " + decrypt);
  }
}


 * Primes.java Generates large prime numbers.
***

import java.math.BigInteger;

/** A few utilities to generate a large random BigInteger,
 *  and find the next prime number above a given BigInteger.
 
public class Primes {
  // Note that BigInteger.ZERO was new in JDK 1.2, and 1.1
  // code is being used to support the most servlet engines.
  private static final BigInteger ZERO = new BigInteger("0");
  private static final BigInteger ONE = new BigInteger("1");
  private static final BigInteger TWO = new BigInteger("2");
  
  // Likelihood of false prime is less than 1/2^ERR_VAL
  // Assumedly BigInteger uses the Miller-Rabin test or
  // equivalent, and thus is NOT fooled by Carmichael numbers.
  // See section 33.8 of Cormen et al. Introduction to
  // Algorithms for details.
  private static final int ERR_VAL = 100;
  
  public static BigInteger nextPrime(BigInteger start) {
    if (isEven(start))
      start = start.add(ONE);
    else
      start = start.add(TWO);
    if (start.isProbablePrime(ERR_VAL))
      return(start);
    else
      return(nextPrime(start));
  }

  private static boolean isEven(BigInteger n) {
    return(n.mod(TWO).equals(ZERO));
  }

  private static StringBuffer[] digits =
    { new StringBuffer("0"), new StringBuffer("1"),
      new StringBuffer("2"), new StringBuffer("3"),
      new StringBuffer("4"), new StringBuffer("5"),
      new StringBuffer("6"), new StringBuffer("7"),
      new StringBuffer("8"), new StringBuffer("9") };

  private static StringBuffer randomDigit() {
    int index = (int)Math.floor(Math.random() * 10);
    return(digits[index]);
  }
  
  public static BigInteger random(int numDigits) {
    StringBuffer s = new StringBuffer("");
    for(int i=0; i 0)
      numDigits = Integer.parseInt(args[0]);
    else
      numDigits = 150;
    BigInteger start = random(numDigits);
    for(int i=0; i<50; i++) {
      start = nextPrime(start);
      System.out.println("Prime " + i + " = " + start);
    }
  }
}

mport java.applet.Applet; import java.awt.
*; 
************************** 
/** Eight ungrouped buttons in an Applet using FlowLayout. * */ 
public class ButtonTest1 extends Applet { 
      public void init() { 
            String[] labelPrefixes = { 
                  "Start", "Stop", "Pause", "Resume" 
      }; 
      for (int i=0; i<4; i++) { 
           add(new Button(labelPrefixes[i] + " Thread1")); 
      } 
      for (int i=0; i<4; i++) { 
           add(new Button(labelPrefixes[i] + " Thread2")); 
      } 
   }  
}