Program to show class Casting in Java

class Casting
{
public static void main(String args[])
{
float sum;
int i;
sum=0.0f;
for(i=1;i<=10;i++)
{
sum=sum+1/(float)i;
System.out.print("i="+i);
System.out.println("sum:"+sum);
}
}
}

Creating Application Server in Java

//import classes
import java.awt.event.*;
import java.net.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.awt.*;

//Code for the AppServer class

class MyFrame extends Frame implements ActionListener
{
MyFrame()
{
setSize(600,400);
setVisible(true);

this.setTitle("Welcome to server");
JPanel panel=new JPanel();
//panel.setBackground(new Color(0,100,100));

setLayout(new FlowLayout());
JButton btnReport;
JButton btnExit;
btnReport=new JButton("Report");
panel.add(btnReport);

btnExit=new JButton("Exit");
panel.add(btnExit);
add(panel);

btnReport.addActionListener(this);
btnExit.addActionListener(this);
setVisible(true);//add listener to the Login button

}

public void actionPerformed(ActionEvent ae)
{
String str = ae.getActionCommand();
if(str.equals("Report"))
{
new Reportjen();

}
else if(str.equals("Exit"))
{
System.exit(0);

}

}

}

public class AppServer implements Runnable
{

ServerSocket server;
Socket fromClient;
Thread serverThread;
InetAddress host;

public AppServer()
{
MyFrame obj=new MyFrame();

System.out.println("Conference Engine started...");
try
{
host = InetAddress.getLocalHost();
System.out.println("Host name:'" + host.getHostName()
+ "' has IP address: " + host.getHostAddress());
server = new ServerSocket(1001);
serverThread = new Thread(this);
serverThread.start();
}

catch (UnknownHostException e)
{
e.printStackTrace();
}

catch(Exception e)
{
System.out.println("Cannot start the thread: " + e);
}
}


public static void main(String args[])
{
new AppServer();

}

public void run()
{
try
{
while(true)
{
//Listening to the clients request
fromClient = server.accept();

//Creating the connect object
Connect con = new Connect(fromClient);
}
}
catch(Exception e)
{
System.out.println("Cannot listen to the client" + e);
}
}

}

//Code for the connect class
class Connect
{
ObjectOutputStream streamToClient;
int ctr=0;

BufferedReader streamFromClient;
static Vector vector;
static Vector vctrList;
String message=" ";
static String str=new String("UsrList");

static
{
vector=new Vector(1,1);
vctrList=new Vector(1,1);
vctrList.addElement((String)str);
}


int verify(String mesg)
{

try
{
RandomAccessFile RAS=new RandomAccessFile("UsrPwd.txt", "r");
int i=0;
String str="";
while((RAS.getFilePointer())!=(RAS.length()))
{
str=RAS.readLine();
if(str.equals(mesg))
{
ctr=1;
break;

}
}
RAS.close();
}
catch(Exception e)
{

}

return ctr;


}//end of verify()

int checkFile(String mesg)
{
int chk=1;
try
{
RandomAccessFile RS=new RandomAccessFile("UsrPwd.txt", "r");
int i=0;

String str="";
String colon=new String(":");
int index=((String)mesg).lastIndexOf(colon);

String userName=(String)mesg.substring(0,index);
while((RS.getFilePointer())!=(int)(RS.length()))
{
str=RS.readLine();
int index1=((String)str).lastIndexOf(colon);
String usrName=(String)str.substring(0,index1);
if(usrName.equals(userName))
{
chk=0;
break;

}
}//end of while
RS.close();
}//end of try
catch(Exception e)
{

}

return chk;


}//end of chkFile


public Connect(Socket inFromClient)
{

//Retrieving the clients stream
String msg="",msg1="";
String mesg="";
try
{
streamFromClient = new BufferedReader(new InputStreamReader(inFromClient.getInputStream()));

streamToClient= new ObjectOutputStream(inFromClient.getOutputStream());

msg=streamFromClient.readLine();
//mesg=streamFromClient.readLine();

if((msg.equals("From Timer")))
{
streamToClient.writeObject(vector);
streamToClient.writeObject(vctrList);
}
else if(msg.equals("LoginInfo"))
{ System.out.println(inFromClient.getInetAddress());

msg=streamFromClient.readLine();
int ver=verify(msg);

if(ver==1)
{
msg1=streamFromClient.readLine();

FileOutputStream out = new FileOutputStream("Loginfo.txt",true);
PrintStream p = new PrintStream( out );
p.println();
p.println(msg1);
p.close();



String colon=new String(":");
int index=((String)msg).lastIndexOf(colon);
String userName=(String)msg.substring(0,index) +inFromClient.getInetAddress();
if(!(vctrList.indexOf((String)userName)>0))
{
streamToClient.writeObject("Welcome"+inFromClient.getInetAddress());
vctrList.addElement((String)userName);
}
}
else
{
streamToClient.writeObject("Login denied");
}
}

else if(msg.equals("RegisterInfo"))
{
msg=streamFromClient.readLine();
int ret=checkFile(msg);
if(ret==0)
streamToClient.writeObject("User Exists");
if(ret==1)
{
FileOutputStream out = new FileOutputStream("UsrPwd.txt",true);
PrintStream p = new PrintStream( out );
p.println();
p.println(msg);
p.close();
streamToClient.writeObject("Registered");
}
}
else if(msg.equals("User Logout"))
{
String remUser=streamFromClient.readLine();
boolean b=vctrList.removeElement((String)remUser);
}
else

{

message=message+msg;
vector.addElement((String)message);
streamToClient.writeObject(vector);

}

}//end of try
catch(Exception e)
{
System.out.println("Cannot get the client stream connect" + e);
}

finally
{
try
{
inFromClient.close();
}
catch(IOException e)
{}
}

}//end of connect
}

Program to find area of Rectangle in java

abstract class Figure
{
double dim1;
double dim2;
Figure(double a, double b)
{
dim1=a;
dim2=b;
}
abstract double area();
}
class Rectangle extends Figure
{
Rectangle(double a, double b)
{
super(a,b);
}
double area()
{
System.out.println("Area of Rectangle");
return(dim1*dim2);
}
}
class Triangle extends Figure
{
Triangle(double a, double b)
{
super(a,b);
}
double area()
{
System.out.println("area of triangle");
return(dim1*dim2/2);
}
}
class AbstractArea
{
public static void main(String args[])
{
Rectangle r=new Rectangle(10,5);
Triangle t=new Triangle(10,2);
Figure figref;
figref=r;
double d1=figref.area();
System.out.println(d1);
figref=t;
double d2=figref.area();
System.out.println(d2);
}
}