this keyword in Java

Here is given the usage of this keyword.

this keyword can be used to refer current class instance variable.

this() can be used to invoke current class constructor.

this keyword can be used to invoke current class method (implicitly)

this can be passed as an argument in the method call.

this can be passed as argument in the constructor call.

this keyword can also be used to return the current class instance.

From - www.DreamsCoder.com

Star Pattern Program in C

/*Star Pattern Program in C

Author - Chinmay Mahajan*/

#include<stdio.h>
#include<conio.h>

void main()
{
int i,j,k,m,o,f,n;
clrscr();
printf("Enter value of n \n");
scanf("%d",&n);
k=n;
o=1;
for(i=0;i<n;i++) //for number of lines
{

for(j=0;j<k;j++) //for left spacing
{
printf("_");
}
for(m=0;m<o;m++) //for Printing *
{
printf(" *");
}

for(f=0;f<k;f++)  //for right spacing
{
printf("_");
}
printf("\n"); //new line
k--;
o++;
}//outer for
}//main

Socket Programming with File Handling

/*Client Socket program that accepts file name from Client and send it to Server, Server Side Socket reads the Content of a file and display them onto the Client Socket*/

/*Server Program (severprac.java)*/

import java.io.*;
import java.net.*;

public class serverprac
{

public static void main(String[] args) {

ServerSocket ss;
Socket client;
String nm;
try
{
ss = new ServerSocket(1212);
System.out.println("Server is Waitng For Client");
client = ss.accept();
System.out.println("Client is Connected");
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
BufferedReader br1 = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintStream ps = new PrintStream(client.getOutputStream());

String filenm = br1.readLine();

File f = new File(".");
File[] flist = f.listFiles();

for(File n:flist)
{
nm = n.getName();
if(nm.equals(filenm))
{

System.out.println("File is Present");
FileReader fr = new FileReader(nm);
BufferedReader bfr = new BufferedReader(fr);
String lne;
while(true)
{


lne = bfr.readLine();

                if (lne == null)
                break;
//System.out.println(lne);

ps.println(lne);
}
}
}


ps.close();
br1.close();
br.close();
ss.close();

}//try
catch(Exception e)
{
System.out.println(e);
}
}//main
}

/*Client Program (clientprac.java)*/

import java.io.*;
import java.net.*;

public class clientprac
{

public static void main(String[] args)
{
Socket s;
try
{
s = new Socket("127.0.0.1",1212);
System.out.println("Clent is Conneccted to the Server");

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
BufferedReader br1 = new BufferedReader(new InputStreamReader(s.getInputStream()));
PrintStream ps = new PrintStream(s.getOutputStream());
System.out.println("Enter File name");
ps.println(br.readLine());
while(br1.readLine() !=null)
System.out.println(br1.readLine());
br1.close();
ps.close();
br.close();
br1.close();
s.close();

}
catch(Exception e)
{
System.out.println(""+e);
}//catch
}//main
}

Inter - Thread communication using wait(), notify() and notify all() method in Java

/*
Write a program to illustrate  inter - thread communication using wait(), notify() and notify all() method
*/

import java.io.*;
class q
{
String msg;
boolean flag;
q()
{
flag=false;
}
synchronized void get()
{
if(flag==false)
{
try
{
wait();
}//try
catch(InterruptedException e)
{

}//catch

}
flag=false;
System.out.println("Received Message"+msg);
notify();
}
synchronized void put(String x)
{
if(flag==true)
{
try
{
wait();
}
catch(InterruptedException e)
{

}//catch

}
msg = x;
flag = true;

if(msg.equalsIgnoreCase("Good Bye"))
System.exit(0);
notify();
}
}


class sender extends Thread{
q q1;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String s;
sender(q x)
{
q1 = x;
start();
}
public void run()
{
while(true)
{
System.out.println("Enter Message ");
try
{
s = br.readLine();
q1.put(s);
}
catch(IOException e)
{

}//catch
}//while
}//run
}

class receiver extends Thread
{
q q2;
receiver(q x)
{
q2 = x;
start();

}

public void run()
{
while(true)
{
q2.get();
}
}
}

class fourteen
{
public static void main(String args[])
{
q q4 = new q();
sender s = new sender(q4);
receiver r = new receiver(q4);
}
}

User Defined Exception Example in Java

/*
Write a class Student with attributes roll no, name, age and course. Initialize values through parameterized constructor. If age of student is not in between 15 and 21 then generate user-defined exception “Age Not Within The Range”.If name contains numbers or special symbols raise exception “Name not valid”
*/

import java.io.*;
class AgeNotWithinRangeException extends Exception
{
AgeNotWithinRangeException()
{
super();
}
}

class NameNotValidException extends Exception
{
NameNotValidException()
{
super();
}
}
class Student
{
private
int roll,age;
String name,course;

public
Student(int r,String nm,int ag,String co)
{
roll=r;
name=nm;
age=ag;
course=co;

System.out.println("Roll Number is "+roll);
System.out.println("Name is "+name);;
System.out.println("Age is "+age);
System.out.println("Course is "+course);
}

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

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int roll,age;
String name,course;
System.out.println("Enter No. :");
roll = Integer.parseInt(br.readLine());
System.out.println("Enter Name :");
name = br.readLine();
try
{
for(int i=0;i<name.length();i++)
{
char c = name.charAt(i);

if((c<65 || c>90) && (c<97 || c>122) && (c!=32))
{
throw new NameNotValidException();
}//if
}//for
}//try
catch(NameNotValidException n)
{
System.out.println("Invalid Name"+n);
}
System.out.println("Enter Age :");
age = Integer.parseInt(br.readLine());
try
{
if(age<15 || age>21)
{
throw new AgeNotWithinRangeException();
}
}//try

catch(AgeNotWithinRangeException e)
{
System.out.println("Invalid Age"+e);
}

System.out.println("Enter Course :");
course = br.readLine();

Student s = new Student(roll,name,age,course);
}
}

Error while Creating New Android Project in Eclipse.

Problem with Eclipse while creating New Android Application 

Solution - In Eclipse go to Window - > Android SDK Manager 

Select one or more SDK Platform and Install them.

Also Update ADT plugins.