Fibonacci

import java.io.*;

class Fibonacci
{
    int i=0,j=1,sum;
    void fib(int lim)
    {
        while(i<=lim)
        {
            System.out.print(i+"\t");
            sum=i+j;
            i=j;
            j=sum;
        }
    }

}

/**
 *
 * @author Sanket
 */

public class Main
{
    public static void main(String args[])throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter limit : ");
        int lim=Integer.parseInt(br.readLine());
       
        Fibonacci f=new Fibonacci();
        f.fib(lim);
    }
}

Palindrome

import java.io.*;

class Palindrome {

    void pali(String s) {
        int a = s.length();
        int mid = (a / 2);
        int count = 0;

        if (a % 2 == 0) {
            f:
            for (int i = 0, j = a - 1; i < mid || j >= mid; i++, j--) {
                if ((s.charAt(i)) == (s.charAt(j))) {
                    count++;
                    continue f;
                } else {
                    break f;
                }
            }
            if (count == mid) {
                System.out.println("word palindrome");
            } else {
                System.out.println("word no palindrome");
            }
        } else {
            j:
            for (int i = 0, j = a - 1; i < mid || j > mid; i++, j--) {
                if (s.charAt(i) == s.charAt(j)) {
                    count++;
                    continue j;
                } else {
                    break j;
                }
            }
            if (count == mid) {
                System.out.println("word palindrome");
            } else {
                System.out.println("word no palndrome");
            }
        }
    }
}

/**
 *
 * @author Sanket
 */
public class Main {
        public static void main(String[] args) throws IOException {
        Palindrome p = new Palindrome();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter Word : ");
        String str = br.readLine();
        p.pali(str);
    }
}

BubleSort Using Two Variables

class BubbleSort
{
    void sort(int a[])
    {
        for(int i=0;i<a.length;i++)
        {
            for(int j=i;j<a.length;j++)
            {
                if(a[i]>a[j])
                {
                    a[i]=a[i]+a[j];
                    a[j]=a[i]-a[j];
                    a[i]=a[i]-a[j];
                }
            }
        }

        System.out.print("Sorted Numbers : ");
       
        for(int i=0;i<a.length;i++)
            System.out.print("\t"+a[i]);
       
        System.out.println("\n");
    }

}


/**
 *
 * @author Sanket
 */
public class Main {
    public static void main(String[] args)throws IOException {
        BubbleSort b=new BubbleSort();

        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Entrer total numbers : ");
        int n=Integer.parseInt(br.readLine());

        int a[]=new int[n];
        for(int i=0;i<n;i++)
        {
            System.out.print("Enter number "+(i+1)+" : ");
            a[i]=Integer.parseInt(br.readLine());
        }
        b.sort(a);
    }
}

File Reader

import java.io.*;
/**
 *
 * @author Sanket
 */
public class Main {
    public static void main(String[] args)throws IOException {
        //to read content from file you have to give complete link of file
        FileReader fr=new FileReader("D:\\sank.doc");
        BufferedReader br=new BufferedReader(fr);

        String str=br.readLine();

        while(str!=null)
        {
            System.out.println(str);
            str=br.readLine();
        }
    }
}

File Writer

import java.io.*;

/**
 *
 * @author Sanket
 */
public class Main {
    public static void main(String[] args)throws IOException {
        File f=new File("D:\\sank.doc");
        f.createNewFile();

        FileWriter fw=new FileWriter(f,true);
        BufferedWriter bw=new BufferedWriter(fw);
        PrintWriter pw=new PrintWriter(bw,true);

        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.println("write here and to stop write 'thanx' : ");
        String str=br.readLine();

        while(!str.equals("thanx"))
        {
            pw.println(str);
            str=br.readLine();
        }
    }
}

Socket Programming (Client - Server)

You have to run Server Program first and then run client program.

CLIENT

import java.io.*;
import java.net.*;
/**
 *
 * @author Sanket
 */
public class Main {
    public static void main(String[] args)throws IOException {
       
        Socket sc=new Socket("127.0.0.1",9068);
        OutputStream os=sc.getOutputStream();
        OutputStreamWriter osw=new OutputStreamWriter(os);
        BufferedWriter bw=new BufferedWriter(osw);
        PrintWriter pw=new PrintWriter(bw,true);

        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        String str=br.readLine();

        while(!str.equals("thanx"))
        {
            pw.println(str);
            str=br.readLine();
        }
    }
}




 SERVER

 import java.io.*;
import java.net.*;
/**
 *
 * @author Sanket
 */
public class Server {
    public static void main(String[] args)throws IOException {
       
        ServerSocket ss=new ServerSocket(9068);
        Socket sc=ss.accept();
        InputStream is=sc.getInputStream();
        InputStreamReader isr=new InputStreamReader(is);

        BufferedReader br=new BufferedReader(isr);
        String str=br.readLine();

        while(!str.equals("end"))
        {
            System.out.println(str);
            str=br.readLine();
        }
    }
}

Challange-Response Authentication

import java.io.*;
import java.util.Random;

/**

 *

 * @author Sanket

 */

public class Main {
    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String originaluser = "sanket";

        f:
        for (int j = 0; j < 3; j++) {
            System.out.print("Eneter User Name : ");
            String username = br.readLine();

            if (originaluser.equals(username)) {
                System.out.println("Valid user name");
                Random rgenerator = new Random();
                int x = rgenerator.nextInt(100);
                int y = x * 10;

                System.out.println("Challenging number is : " + x);
                System.out.print("Enter Password : ");
                int pass = Integer.parseInt(br.readLine());

                f1:
                for (int z = 0; z < 3; z++) {
                    if (z == 1 || z == 2) {
                        System.out.println("Retype password : ");
                        pass = Integer.parseInt(br.readLine());
                    }
                    if (pass == y) {
                        System.out.println("valid user");
                        break f;
                    } else {
                        System.out.println("invalid password");
                        if (z == 2) {
                            System.out.println("access denied");
                            break f;
                        }
                    }
                }
            } else {
                System.out.println("Invalid user name");
                if (j == 2) {
                    System.out.println("access denied");
                }
            }
        }
    }
}