Master Coding: 2011

Friday, 15 July 2011

Wednesday, 13 July 2011

Saturday, 2 July 2011

Notepad

import java.awt.*;
import java.awt.event.*;
import java.awt.datatransfer.*;
import java.io.*;
public class Editor extends Frame
   {
   String filename;
   TextArea tx;
   Clipboard clip = getToolkit().getSystemClipboard();
   Editor()
   {
   setLayout(new GridLayout(1,1));
   tx = new TextArea();
   add(tx);
   MenuBar mb = new MenuBar();
   Menu F = new Menu("file");
   MenuItem n = new MenuItem("New");
   MenuItem o = new MenuItem("Open");
   MenuItem s = new MenuItem("Save");
   MenuItem e = new MenuItem("Exit");
   n.addActionListener(new New());
   F.add(n);
   o.addActionListener(new Open());
   F.add(o);
   s.addActionListener(new Save());
   F.add(s);
   e.addActionListener(new Exit());
   F.add(e);
   mb.add(F);
   Menu E = new Menu("Edit");
   MenuItem cut = new MenuItem("Cut");
   MenuItem copy = new MenuItem("Copy");
   MenuItem paste = new MenuItem("Paste");
   cut.addActionListener(new Cut());
   E.add(cut);
   copy.addActionListener(new Copy());
   E.add(copy);
   paste.addActionListener(new Paste());
   E.add(paste);
   mb.add(E);
   setMenuBar(mb);

   mylistener mylist = new mylistener();
   addWindowListener(mylist);
   }

   class mylistener extends WindowAdapter
   {
   public void windowClosing (WindowEvent e)
   {
   System.exit(0);
   }
   }

   class New implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   tx.setText(" ");
   setTitle(filename);
   }
   }

   class Open implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   FileDialog fd = new FileDialog(Editor.this, "select File",FileDialog.LOAD);
   fd.show();
   if (fd.getFile()!=null)
   {
   filename = fd.getDirectory() + fd.getFile();
   setTitle(filename);
   ReadFile();
   }
   tx.requestFocus();
   }
   }

   class Save implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   FileDialog fd = new FileDialog(Editor.this,"Save File",FileDialog.SAVE);
   fd.show();
   if (fd.getFile()!=null)
   {
   filename = fd.getDirectory() + fd.getFile();
   setTitle(filename);
   try
   {
   DataOutputStream d = new DataOutputStream(new FileOutputStream(filename));
   String line = tx.getText();
   BufferedReader br = new BufferedReader(new StringReader(line));
   while((line = br.readLine())!=null)
   {
   d.writeBytes(line + "\r\n");
   d.close();
   }
   }
   catch(Exception ex)
   {
   System.out.println("File not found");
   }
   tx.requestFocus();
   }
   }
   }

   class Exit implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   System.exit(0);
   }
   }
   void ReadFile()
   {
   BufferedReader d;
   StringBuffer sb = new StringBuffer();
   try
   {
   d = new BufferedReader(new FileReader(filename));
   String line;
   while((line=d.readLine())!=null)
   sb.append(line + "\n");
   tx.setText(sb.toString());
   d.close();
   }
   catch(FileNotFoundException fe)
   {
   System.out.println("File not Found");
   }
   catch(IOException ioe){}
   }

   class Cut implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   String sel = tx.getSelectedText();
   StringSelection ss = new StringSelection(sel);
   clip.setContents(ss,ss);
   tx.replaceRange(" ",tx.getSelectionStart(),tx.getSelectionEnd());
   }
   }

   class Copy implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   String sel = tx.getSelectedText();
   StringSelection clipString = new StringSelection(sel);
   clip.setContents(clipString,clipString);
   }
   }

   class Paste implements ActionListener
   {
   public void actionPerformed(ActionEvent e)
   {
   Transferable cliptran = clip.getContents(Editor.this);
   try
   {
   String sel = (String) cliptran.getTransferData(DataFlavor.stringFlavor);
   tx.replaceRange(sel,tx.getSelectionStart(),tx.getSelectionEnd());
   }
   catch(Exception exc)
   {
   System.out.println("not string flavour");
   }
   }
   }

   public static void main(String args[])
   {
   Frame f = new Editor();
   f.setSize(500,400);
   f.setVisible(true);
   f.show();
   }
}

NegativeLength Exception

NegativeLength Exception

import java.io.*;
   public class NegativeLengthException extends Exception {

   /** Test NegativeLengthException */

   public static void main(String[] args) {
   try {
   int lineLength = readLength();
   for(int i=0; i System.out.print("*");
   }
   System.out.println();
   } catch (NegativeLengthException nle) {
   System.out.println("NegativeLengthException: " +
   nle.getMessage());
   }
   }

   public NegativeLengthException() {
   super("Negative dimensions not permitted.");
   }

   public NegativeLengthException(String message) {
   super(message);
   }

   // readLength catches IOExceptions locally but lets the
   // calling method handle NegativeLengthExceptions.
   private static int readLength() throws NegativeLengthException {
   BufferedReader in = new BufferedReader(
   new InputStreamReader(System.in));
   System.out.print("Enter length: ");
   System.out.flush();
   int len = 0;
   try {
   String line = in.readLine();
   len = Integer.parseInt(line);
   if (len < 0) {
   throw new NegativeLengthException();
   }
   } catch (IOException ioe) {
   System.out.println("Problem reading from keyboard");
   }
   return(len);
   }
}

Moving a File or Directory to Another Directory

Moving a File or Directory to Another Directory

   public static void main(String args[]){
   try{
   // File (or directory) to be moved
   File file = new File("file.txt");

   // Destination directory
   File dir = new File("gg");

   // Move file to new directory
   boolean success = file.renameTo(new File(dir, file.getName()));
   if (!success) {
   System.out.println("File moved");
   }
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}

Method Overriding

Method Overriding

class A {
   String name() { return "A"; }
}

   class B extends A {
   String name() { return "B"; }
}

   class C extends A {
   String name() { return "C"; }
}

   public class Overriding {
   public static void main(String[] args) {
   A[] tests = new A[] { new A(), new B(), new C() };

   for (int i = 0; i < tests.length; i++)
   System.out.print(tests[i].name());
   }
}

Method Overloading

Method Overloading

import java.awt.Container;
import javax.swing.*;
public class MethodOverload extends JApplet
   {
   JTextArea outputArea;
   public void init()
   {
   outputArea = new JTextArea( 2, 20 );
   Container c = getContentPane();
   c.add( outputArea );

   outputArea.setText(
   "The square of integer 7 is " + square( 7 ) +
   "\nThe square of double 7.5 is " + square( 7.5 ) );
   }

   public int square( int x )
   {
   return x * x;
   }

   public double square( double y )
   {
   return y * y;
   }
}

Making the application wait for some given time

Making the application wait for some given time

import java.util.*;

public class WaitForSomeTime
   {
   public static void main(String args[])
   {
   WaitForSomeTime waitForSomeTime = new WaitForSomeTime();
   waitForSomeTime.myMethod();
   }

   public void myMethod()
   {
   System.out.println("Starting......");

   // pause for a while
   Thread thisThread = Thread.currentThread();
   try
   {
   thisThread.sleep(10000);
   }
   catch (Throwable t)
   {
   throw new OutOfMemoryError("An Error has occured");
   }
   System.out.println("Ending......");

   }
}

Friday, 1 July 2011

Listing the Files or Subdirectories in a Directory

Listing the Files or Subdirectories in a Directory

   public static void main(String args[]){
   try{
   File dir = new File("d:\\temp");

   String[] children = dir.list();
   if (children == null) {
   System.out.println("Directory does not exist or is not a Directory");
   } else {
   for (int i=0; i // Get filename of file or directory
   String filename = children[i];
   System.out.println(filename);
   }
   }

   // It is also possible to filter the list of returned files.
   // This example does not return any files that start with `.'.
   FilenameFilter filter = new FilenameFilter() {
   public boolean accept(File dir, String name) {
   return !name.startsWith(".");
   }
   };
   children = dir.list(filter);


   // The list of files can also be retrieved as File objects
   File[] files = dir.listFiles();

   // This filter only returns directories
   FileFilter fileFilter = new FileFilter() {
   public boolean accept(File file) {
   return file.isDirectory();
   }
   };
   files = dir.listFiles(fileFilter);
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}

Listing the File System Roots

Listing the File System Roots

   public static void main(String args[]){
   try{
   File[] roots = File.listRoots();
   for (int i=0; i System.out.println((roots[i]));
   }
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}

Listing All Available Unicode to Character Set Converters

Listing All Available Unicode to Character Set Converters

public static void main(String args[])
   {
   Map map = Charset.availableCharsets();
   Iterator it = map.keySet().iterator();
   while (it.hasNext()) {
   // Get charset name
   String charsetName = (String)it.next();
   System.out.println("Charset Name "+charsetName);

   // Get charset
   Charset charset = Charset.forName(charsetName);
   System.out.println("Charset "+charset);
   }
}

List all '.java' files present in a directory.

List all '.java' files present in a directory.

import java.io.*;

public class FileExt
   {
   public static void main(String args[])
   {
   try
   {
   String[] filesList;
   File dir = new File(".");
   filesList= dir.list(new FileFilter());

   for (int i=0;i {
   System.out.println(filesList[i]);
   }
   }
   catch(Exception e){}
   }
}

class FileFilter implements FilenameFilter
   {
   public boolean accept(File dir, String name)
   {
   return (name.endsWith(".java"));
   }
}

Linear Search of an Array

Linear Search of an Array

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

public class LinearSearch extends JApplet implements ActionListener
   {
   JLabel enterLabel, resultLabel;
   JTextField enter, result;
   int a[];

   public void init()
   {
   Container c = getContentPane();
   c.setLayout( new FlowLayout() );

   enterLabel = new JLabel( "Enter integer search key" );
   c.add( enterLabel );

   enter = new JTextField( 10 );
   enter.addActionListener( this );
   c.add( enter );

   resultLabel = new JLabel( "Result" );
   c.add( resultLabel );

   result = new JTextField( 20 );
   result.setEditable( false );
   c.add( result );

   // create array and populate with even integers 0 to 198
   a = new int[ 100 ];

   for ( int i = 0; i < a.length; i++ )
   a[ i ] = 2 * i;

   }

   // Search "array" for the specified "key" value
   public int linearSearch( int array[], int key )
   {
   for ( int n = 0; n < a.length; n++ )
   if ( array[ n ] == key )
   return n;

   return -1;
   }

   public void actionPerformed( ActionEvent e )
   {
   String searchKey = e.getActionCommand();

   // Array a is passed to linearSearch even though it
   // is an instance variable. Normally an array will
   // be passed to a method for searching.
   int element = linearSearch( a, Integer.parseInt( searchKey ) );

   if ( element != -1 )
   result.setText( "Found value in element " + element );
   else
   result.setText( "Value not found" );
   }
}

Java Script Trim() function

Java Script Trim() function

   function fnTrim() {
   for(var L=0; L if(this.charAt(L)!=" ")break;
   for(R=this.length-1; R>=0;R--)
   if(this.charAt(R)!=" ")break;
   if(L==this.length)return "";
   return this.substring(L,R+1);
}
String.prototype.trim=fnTrim;
//**** For trim the crtl

   if ((document.frm.crtlName.value).trim()=="") {
   //*** Here ur code

}

Information Servlet

// Import standard networking I/O packages

import java.net.*;

import java.io.*;

// Enumeration from util

import java.util.Enumeration;

// Import servlet packages

import javax.servlet.*;

import javax.servlet.http.*;

//

// InfoServlet

//

public class InfoServlet extends HttpServlet

{

// Get method of servlet

public void doGet (HttpServletRequest request, HttpServletResponse response) throws IOException

{

// Define content type

response.setContentType("text/html");

// Get information about client and server

String clientBrowser = request.getHeader("User-Agent");

String clientReferer = request.getHeader("Referer");

String clientIP = request.getRemoteAddr();

String serverOS = System.getProperty("os.name");

String serverOSVersion = System.getProperty("os.version");

String serverOSArch = System.getProperty("os.arch");

// Get a servlet output stream for the response

ServletOutputStream sout = response.getOutputStream();

// Print header information

sout.println ("<HTML><HEAD><TITLE>InfoServlet Response</TITLE></HEAD>");

// Print body information

sout.println ("<BODY BGCOLOR='white' COLOR='black'>");

sout.println ("<H2>InfoServlet</H2><HR>");

// Print information about client

sout.println ("<H3>Client :-</H3>");

// Check for presence of user-agent header field

if (clientBrowser != null)

sout.println ("User-Agent : " + clientBrowser + "<BR>");

// Print IP address

sout.println ("IP Address : " + clientIP + "<BR>");

// Check for presence of referer header field

if (clientReferer != null)

sout.println ("Last page : " + clientReferer + "<BR>");

// Print information about server

sout.println ("<H3>Server</H3>");

// Check to see if each property is valid, and if so, output it

if ( (serverOS != null) & (serverOSVersion != null) )

sout.println ("Server O/S : " + serverOS + " v" + serverOSVersion + "<BR>");

if ( serverOSArch != null)

sout.println ("Server CPU : " + serverOSArch + "<BR>");

// Obtain a reference to the server context

ServletContext context = getServletContext();

if (context != null)

{

// Display information about servlets

sout.println ("<h3> Servlet information </h3>");

// Table for servlet info

sout.println ("<table border='1' width=70%>");

sout.println ("<tr><td><b>Servlet Name</b></td></tr>");

for (Enumeration e = context.getServletNames(); e.hasMoreElements();)

{

// Get name of servlet

String name = (String) e.nextElement();

sout.println ("<tr> <td>");

sout.println (name);

sout.println ("</td> </tr>");

}

sout.println ("</table>");

}

else

sout.println ("Could not determine servlet context");

// Write footer information

sout.println ("</BODY></HTML>");

// Flush

sout.flush();

}

// Post method of servlet

public void doPost (HttpServletRequest request, HttpServletResponse response) throws IOException

{

// Perform same action as get method

doGet(request, response);

}

public String getServletInfo()

{

return new String (

"InfoServlet - reports information on client connection and server state"

);

}

Histogram printing program

Histogram printing program

import javax.swing.*;

public class Histogram
   {
   public static void main( String args[] )
   {
   int n[] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 };
   String output = "";

   output += "Element\tValue\tHistogram";

   for ( int i = 0; i < n.length; i++ )
   {
   output += "\n" + i + "\t" + n[ i ] + "\t";

   for ( int j = 1; j <= n[ i ]; j++ ) // print a bar
   output += "*";
   }

   JTextArea outputArea = new JTextArea( 11, 30 );
   outputArea.setText( output );

   JOptionPane.showMessageDialog( null, outputArea,"Histogram Printing Program",JOptionPane.INFORMATION_MESSAGE );

   System.exit( 0 );
   }
}

Getting and Setting the Modification Time of a File or Directory

Getting and Setting the Modification Time of a File or Directory

   public static void main(String args[]){
   try{
   File file = new File("file.txt");

   // Get the last modified time
   long modifiedTime = file.lastModified();
   // 0L is returned if the file does not exist

   // Set the last modified time
   long newModifiedTime = System.currentTimeMillis();
   boolean success = file.setLastModified(newModifiedTime);
   if (!success) {
   System.out.println("Operation failed");
   }
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}

Get hashtable keys from value

Get hashtable keys from value

class keyhash
   {
   ResultSet rs;
   Hashtable hash;
   Vector v;
   static int i;
   Enumeration e;

   public static void main(String[] args)
   {
   keyhash gs = new keyhash();
   System.out.println("Hello World!");
   gs.getresultset();
   }

   public void getresultset()
   {
   Hashtable hash = new Hashtable();
   Vector v = new Vector();
   boolean connected = dbConnect();
   // Establish database connection here

   if(connected == true)
   {
   try{
   PreparedStatement getArticles = db.con.prepareStatement
   ("select * from xx where id = ?"
   // sample query

   )


   String artid;
   getArticles.setInt(1, 4);
   //This passes integer 4 as a parameter in
   //the sql query


   rs = getArticles.executeQuery();

   while (rs.next() == true)

   {
   key = rs.getString(1);

   value = rs.getString(2);

   hash.put(key,value);
   //Hashtable populated

   }

   fillvector(hash,v);
   getkeys(v);
   rs.close();
   }
   catch(Exception ex){

   ex.printStackTrace();
   }
   }

   }
   public void fillvector(Hashtable hash,Vector v)
   {
   int j=0;
   boolean success;
   Enumeration e = hash.keys();
   while(e.hasMoreElements())
   {
   String key = (String)(e.nextElement());
   String value = (String)hash.get(key);


   if(value.matches("*****"))
   //Put the value here to retrieve the
   // corresponding keys
   {
   v.addElement(key);
   //Add the corresponding keys to the vector
   }
   }

   }
   public void getkeys(Vector v)
   {
   Enumeration ev= v.elements();
   while (ev.hasMoreElements())
   {
   System.out.println(ev.nextElement());
   // Print the keys related to a single value
   }

   }

}

Formatting real number with Decimal

Formatting real number with Decimal

import java.text.*;
   public class NumFormat {
   public static void main (String[] args) {
   DecimalFormat science = new DecimalFormat("0.000E0");
   DecimalFormat plain = new DecimalFormat("0.0000");

   for(double d=100.0; d<140.0; d*=1.10) {
   System.out.println("Scientific: " + science.format(d) +
   " and Plain: " + plain.format(d));
   }
   }
}

Float datatype

Float datatype

// Static factory version of complex class
   public class Complex1 {
   private final float re;
   private final float im;

   private Complex1(float re, float im) {
   this.re = re;
   this.im = im;
   }

   public static Complex1 valueOf(float re, float im) {
   return new Complex1(re, im);
   }

   public static Complex1 valueOfPolar(float r, float theta) {
   return new Complex1((float) (r * Math.cos(theta)),
   (float) (r * Math.sin(theta)));
   }

   // Accessors with no corresponding mutators
   public float realPart() { return re; }
   public float imaginaryPart() { return im; }

   public Complex1 add(Complex1 c) {
   return new Complex1(re + c.re, im + c.im);
   }

   public Complex1 subtract(Complex1 c) {
   return new Complex1(re - c.re, im - c.im);
   }

   public Complex1 multiply(Complex1 c) {
   return new Complex1(re*c.re - im*c.im,
   re*c.im + im*c.re);
   }

   public Complex1 divide(Complex1 c) {
   float tmp = c.re*c.re + c.im*c.im;
   return new Complex1((re*c.re + im*c.im)/tmp,
   (im*c.re - re*c.im)/tmp);
   }

   public boolean equals(Object o) {
   if (o == this)
   return true;
   if (!(o instanceof Complex1))
   return false;
   Complex1 c = (Complex1)o;
   return (Float.floatToIntBits(re) ==
   Float.floatToIntBits(c.re)) &&
   (Float.floatToIntBits(im) ==
   Float.floatToIntBits(im));
   }
   public int hashCode() {
   int result = 17 + Float.floatToIntBits(re);
   result = 37*result + Float.floatToIntBits(im);
   return result;
   }

   public String toString() {
   return "(" + re + " + " + im + "i)";
   }

   // Public constants
   public static final Complex1 ZERO = new Complex1(0, 0);
   public static final Complex1 ONE = new Complex1(1, 0);
   public static final Complex1 I = new Complex1(0, 1);

   public static void main(String args[]) {
   Complex1 x = Complex1.valueOf(2, 3);
   Complex1 y = Complex1.valueOf(2,-3);
   System.out.println(x + " + " + y + " = " + x.add(y));
   System.out.println(x + " - " + y + " = " + x.subtract(y));
   System.out.println(x + " * " + y + " = " + x.multiply(y));
   System.out.println(x + " / " + y + " = " + x.divide(y));
   System.out.println(x.divide(y).multiply(y));

   Complex1 z = Complex1.valueOfPolar(1, (float) (Math.PI/4));
   Complex1 w = Complex1.valueOf(z.realPart(), -z.imaginaryPart());
   System.out.println(z + " * " + w + " = " + z.multiply(w));
   }
}

Finding the maximum of three doubles

Finding the maximum of three doubles

import java.awt.Container;
import javax.swing.*;
public class DoubleMax extends JApplet
   {
   public void init()
   {
   JTextArea outputArea = new JTextArea();

   String s1 = JOptionPane.showInputDialog( "Enter first floating-point value" );
   String s2 = JOptionPane.showInputDialog( "Enter second floating-point value" );
   String s3 = JOptionPane.showInputDialog( "Enter third floating-point value" );

   double number1 = Double.parseDouble( s1 );
   double number2 = Double.parseDouble( s2 );
   double number3 = Double.parseDouble( s3 );

   double max = maximum( number1, number2, number3 );

   outputArea.setText( "number1: " + number1 + "\nnumber2: " + number2 + "\nnumber3: " + number3 +
   "\nmaximum is: " + max );

   // get the applet's GUI component display area
   Container c = getContentPane();

   // attach outputArea to Container c
   c.add( outputArea );
   }

   // maximum method definition
   public double maximum( double x, double y, double z )
   {
   return Math.max( x, Math.max( y, z ) );
   }
}

Find Numeric filter

Find Numeric filter

class FindNumFilter {
   /** The value of this filter */
   int num;
   /** Constants for the comparison operators. */
   final int LE = -2, LT = -1, EQ = 0, GT = +1, GE = +2;
   /** The current comparison operator */
   int mode = EQ;

   /** Constructor */
   FindNumFilter(String input) {
   switch(input.charAt(0)) {
   case '+': mode = GT; break;
   case '-': mode = LT; break;
   case '=': mode = EQ; break;
   // No syntax for LE or GE yet.
   }
   num = Math.abs(Integer.parseInt(input));
   }

   /** Construct a NumFilter when you know its mode and value */
   FindNumFilter(int mode, int value) {
   this.mode = mode;
   num = value;
   }
   boolean accept(int n) {
   switch(mode) {
   case GT: return n > num;
   case EQ: return n == num;
   case LT: return n < num;
   default:
   System.err.println("UNEX CASE " + mode );
   return false;
   }
   }
}

File Input and Output Stream

File Input and Output Stream

import java.io.*;

   class FileIO {

   public static void main(String[] args) {

   System.out.println("Enter some numbers.");
   StreamTokenizer st = new StreamTokenizer(
   new BufferedReader(new InputStreamReader(System.in)));
   File f = new File("temp.out");
   int numberCount = 0;
   try {
   DataOutputStream dos = new DataOutputStream(
   new BufferedOutputStream(new FileOutputStream(f)));
   while (st.nextToken() != st.TT_EOF) {
   if (st.ttype == st.TT_NUMBER) {
   dos.writeDouble(st.nval);
   numberCount++;
   }
   }
   System.out.println("numberCount=" + numberCount);
   dos.flush();
   dos.close();
   DataInputStream dis = new DataInputStream(
   new BufferedInputStream(new FileInputStream(f)));
   for (int i = 0; i < numberCount; i++) {
   System.out.println("number=" + dis.readDouble());
   }
   dis.close();
   } catch (IOException e) {
   System.err.println("FileIO: " + e);
   } finally {
   f.delete();
   }
   }
}

/* ............... Example compile and run(s)

% javac file.java

% java FileIO
Enter some numbers.
1 2 3
4.4 5.5
6.67
^D
numberCount=6
number=1.0
number=2.0
number=3.0
number=4.4
number=5.5
number=6.67
... end of example run(s) */

Fibonacci numbers (Right side)

Fibonacci numbers (Right side)

import java.text.*;

   public class TestRight {
   public static void main(String args[]) {
   long f1 = 1;
   long f2 = 1;
   RightFormat rf = new RightFormat(20);

   System.out.println("Test of RightFormat(20) on Fibonacci numbers:");
   for(int ix = 0; ix < 32; ix++) {
   System.out.println(rf.format(Long.toString(f1)));
   System.out.println(rf.format(Long.toString(f2)));
   f1 = f1 + f2;
   f2 = f2 + f1;
   }
   }
}

Empty Directory

Empty Directory

import java.io.*;
//DANGEROUS Program to empty a directory

   public class Empty {
   public static void main(String[] argv) {
   if (argv.length != 1) { // no progname in argv[0]
   System.err.println("usage: Empty dirname");
   System.exit(1);
   }

   File dir = new File(argv[0]);
   if (!dir.exists()) {
   System.out.println(argv[0] + " does not exist");
   return;
   }

   String[] info = dir.list();
   for (int i=0; i File n = new File(argv[0] + dir.separator + info[i]);
   if (!n.isFile()) // skip ., .., other directories too
   continue;
   System.out.println("removing " + n.getPath());
   if (!n.delete())
   System.err.println("Couldn't remove " + n.getPath());
   }
   }
}

Double Array

Double Array

// Double-subscripted array example
import java.awt.*;
import javax.swing.*;

public class DoubleArray extends JApplet
   {
   int grades[][] = { { 77, 68, 86, 73 }, { 96, 87, 89, 81 }, { 70, 90, 86, 81 } };

   int students, exams;
   String output;
   JTextArea outputArea;

   // initialize instance variables
   public void init()
   {
   students = grades.length;
   exams = grades[ 0 ].length;

   outputArea = new JTextArea();
   Container c = getContentPane();
   c.add( outputArea );

   // build the output string
   output = "The array is:\n";
   buildString();

   output += "\n\nLowest grade: " + minimum() +
   "\nHighest grade: " + maximum() + "\n";

   for ( int i = 0; i < students; i++ )
   output += "\nAverage for student " + i + " is " + average( grades[ i ] );

   outputArea.setFont( new Font( "Courier", Font.PLAIN, 12 ) );
   outputArea.setText( output );
   }

   // find the minimum grade
   public int minimum()
   {
   int lowGrade = 100;

   for ( int i = 0; i < students; i++ )
   for ( int j = 0; j < exams; j++ )
   if ( grades[ i ][ j ] < lowGrade )
   lowGrade = grades[ i ][ j ];

   return lowGrade;
   }


   // find the maximum grade
   public int maximum()
   {
   int highGrade = 0;

   for ( int i = 0; i < students; i++ )
   for ( int j = 0; j < exams; j++ )
   if ( grades[ i ][ j ] > highGrade )
   highGrade = grades[ i ][ j ];

   return highGrade;
   }

   // determine the average grade for a particular
   // student (or set of grades)
   public double average( int setOfGrades[] )
   {
   int total = 0;

   for ( int i = 0; i < setOfGrades.length; i++ )
   total += setOfGrades[ i ];

   return ( double ) total / setOfGrades.length;
   }

   // build output string
   public void buildString()
   {
   output += " "; // used to align column heads

   for ( int i = 0; i < exams; i++ )
   output += "[" + i + "] ";

   for ( int i = 0; i < students; i++ )
   {
   output += "\ngrades[" + i + "] ";

   for ( int j = 0; j < exams; j++ )
   output += grades[ i ][ j ] + " ";
   }
   }
}

DOS Calculator

DOS Calculator

public class Calculator {
   public static abstract class Operation {
   private final String name;

   Operation(String name) { this.name = name; }

   public String toString() { return this.name; }

   // Perform arithmetic op represented by this constant
   abstract double eval(double x, double y);

   // Doubly nested anonymous classes
   public static final Operation PLUS = new Operation("+") {
   double eval(double x, double y) { return x + y; }
   };
   public static final Operation MINUS = new Operation("-") {
   double eval(double x, double y) { return x - y; }
   };
   public static final Operation TIMES = new Operation("*") {
   double eval(double x, double y) { return x * y; }
   };
   public static final Operation DIVIDE = new Operation("/") {
   double eval(double x, double y) { return x / y; }
   };
   }

   // Return the results of the specified calculation
   public double calculate(double x, Operation op, double y) {
   return op.eval(x, y);
   }
}

   public class CalcTest {
   public static void main(String args[]) {
   double x = Double.parseDouble(args[0]);
   double y = Double.parseDouble(args[1]);

   operate(x, Calculator.Operation.PLUS, y);
   operate(x, Calculator.Operation.MINUS, y);
   operate(x, Calculator.Operation.TIMES, y);
   operate(x, Calculator.Operation.DIVIDE, y);
   }

   static void operate(double x, Calculator.Operation op, double y) {
   Calculator c = new Calculator();
   System.out.println(x + " " + op + " " + y + " = " +
   c.calculate(x, op, y));
   }
}

Determining When an Object Is No Longer Used

Determining When an Object Is No Longer Used

// Create the weak reference.
ReferenceQueue rq = new ReferenceQueue();
WeakReference wr = new WeakReference(object, rq);

// Wait for all the references to the object.
   try {
   while (true) {
   Reference r = rq.remove();
   if (r == wr) {
   // Object is no longer referenced.
   }
   }
   } catch (InterruptedException e) {
}

Determining If Two Filename Paths Refer to the Same File

Determining If Two Filename Paths Refer to the Same File

   public static void main(String args[]){
   try{
   File file1 = new File("gg/file.txt");
   File file2 = new File("file.txt");

   // Filename paths are not equal
   boolean b = file1.equals(file2); // false

   // Normalize the paths
   try {
   file1 = file1.getCanonicalFile(); // c:\almanac1.4\filename
   file2 = file2.getCanonicalFile(); // c:\almanac1.4\filename
   } catch (IOException e) {
   }

   // Filename paths are now equal
   b = file1.equals(file2); // true
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}

Detect ASCII values

Detect ASCII values

BufferedReader inStream=new BufferedReader(new InputStreamReader(System.in));
int a;

for(int i=1;i<=26;i++)
   {

   System.out.println("please enter a character: ");
   a=(int)System.in.read();
   System.out.println("The integer code for " +(char)a+ " is " +(int)a);
   inStream.readLine();
}

Deserializing an Object

Deserializing an Object

   public static void main(String args[]){
   try{
   // Deserialize from a file
   File file = new File("filename.ser");
   ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
   // Deserialize the object
   javax.swing.JButton button = (javax.swing.JButton) in.readObject();
   in.close();

   // Get some byte array data
   byte[] bytes = getBytesFromFile(file);
   // see e36 Reading a File into a Byte Array for the implementation of this method

   // Deserialize from a byte array
   in = new ObjectInputStream(new ByteArrayInputStream(bytes));
   button = (javax.swing.JButton) in.readObject();
   in.close();
   }
   catch (Exception ioe){
   ioe.printStackTrace();
   }
}