# 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")); 
      } 
   }  
}

import java.awt.*;

/** A Circle component built using a Canvas. 
 *
  */

public class Circle extends Canvas {
  private int width, height;        
        
  public Circle(Color foreground, int radius) {
    setForeground(foreground);
    width = 2*radius;
    height = 2*radius;
    setSize(width, height);
  }

  public void paint(Graphics g) {
    g.fillOval(0, 0, width, height);
  }

  public void setCenter(int x, int y) {
    setLocation(x - width/2, y - height/2);
  }
}

WindowUtilities.java Simplifies the setting of native look and feel. 
####################
import javax.swing.*;
import java.awt.*;   // For Color and Container classes.

/** A few utilities that simplify using windows in Swing. 
 *
###################

public class WindowUtilities {

  /** Tell system to use native look and feel, as in previous
   *  releases. Metal (Java) LAF is the default otherwise.
   */

  public static void setNativeLookAndFeel() {
    try {
     UIManager.setLookAndFeel(
       UIManager.getSystemLookAndFeelClassName());
    } catch(Exception e) {
      System.out.println("Error setting native LAF: " + e);
    }
  }

  public static void setJavaLookAndFeel() {
    try {
     UIManager.setLookAndFeel(
       UIManager.getCrossPlatformLookAndFeelClassName());
    } catch(Exception e) {
      System.out.println("Error setting Java LAF: " + e);
    }
  }

   public static void setMotifLookAndFeel() {
    try {
      UIManager.setLookAndFeel(
        "com.sun.java.swing.plaf.motif.MotifLookAndFeel");
    } catch(Exception e) {
      System.out.println("Error setting Motif LAF: " + e);
    }
  }

  /** A simplified way to see a JPanel or other Container. Pops
   *  up a JFrame with specified Container as the content pane.
   */

  public static JFrame openInJFrame(Container content,
                                    int width,
                                    int height,
                                    String title,
                                    Color bgColor) {
    JFrame frame = new JFrame(title);
    frame.setBackground(bgColor);
    content.setBackground(bgColor);
    frame.setSize(width, height);
    frame.setContentPane(content);
    frame.addWindowListener(new ExitListener());
    frame.setVisible(true);
    return(frame);
  }

  /** Uses Color.white as the background color. */

  public static JFrame openInJFrame(Container content,
                                    int width,
                                    int height,
                                    String title) {
    return(openInJFrame(content, width, height,
                        title, Color.white));
  }

  /** Uses Color.white as the background color, and the
   *  name of the Container's class as the JFrame title.
   */

  public static JFrame openInJFrame(Container content,
                                    int width,
                                    int height) {
    return(openInJFrame(content, width, height,
                        content.getClass().getName(),
                        Color.white));
  }
}