Tag Archives: java

What is Queue?

Queues are dynamic collections which have some concept of order. This can be either based on order of entry into the queue - giving us First-In-First-Out (FIFO) or Last-In-First-Out (LIFO) queues. Both of these can be built with linked lists: the simplest "add-to-head" implementation of a linked list gives LIFO behaviour. A minor modification - adding a tail pointer and adjusting the addition method implementation - will produce a FIFO queue.

Queue Implementation

package queue

import java.util.Scanner;

public class Queue {

int[] arr = new int[10];
int a = -1;
int b=0;
public void enqueue(int i){

if(a==9){

System.out.println("Queue is full");

}

else
arr[++a]=i;

}
public void dequeue(){

if(a>b){

for(b=0; b

arr[b]=arr[b+1];

}
a--;
b=0;
}

}

public void display(){

for(int i=0; i<=9; i++){

System.out.println("values at index "+i+":"+arr[i]);

}

}

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);
Queue q = new Queue();
int var = -1;
while( var !=0 ){

System.out.println("1. Insert item in queue");
System.out.println("2. Delete item from queue");
System.out.println("3. Display Queue");
System.out.println("0. Exit");
var = sc.nextInt();
switch(var){

case 1:
System.out.print("Enter item in Queue: ");
int pushItem = sc.nextInt();
q.enqueue(pushItem);
break;
case 2:

q.dequeue();
break;
case 3:
q.display();
break;
}
}

}
}

In this tutorial , i will teach you about a database connectivity with mysql database using java programming language.

As java is a object oriented programming language so the best approach to follow is :

1. Make a individual package for a database.

1.1 In this package create a class for database connectivity.

2. Make a individual packages for each of tables in a database.

2.1 In each of package make a bean class of a particular table.

2.2 Make a class for a task which you want to do. (e.g Selection , insertion etc ).

The following code is for a database connectivity with mysql refer to step 1 and 1.1

 DatabaseConnection.java

package database;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Scanner;
public class DatabaseConnection {

public static Connection con;

public static void init() throws Exception{
String JDBC_DRIVER   = "com.mysql.jdbc.Driver";
String JDBC_URL      = "jdbc:mysql://localhost:3306/test";
String JDBC_USER     = "root";
String JDBC_PASSWORD = "";

Class.forName(JDBC_DRIVER);
con = (Connection)
DriverManager.getConnection(JDBC_URL,JDBC_USER,JDBC_PASSWORD);
System.out.println("Driver Loaded Sucessfully");

}//end init
}

now i want to fetch record so i follow the step no 2.

for example create EmployeeBean.java class. In a bean class we have only setters and getter of a properties.

package employee;
public class EmployeeBean {
private int emp_id;
private String emp_name;
private String emp_fname;
private String emp_surname;

public int getEmp_id() {
return emp_id;
}
public void setEmp_id(int emp_id) {
this.emp_id = emp_id;
}
public String getEmp_name() {
return emp_name;
}
public void setEmp_name(String emp_name) {
this.emp_name = emp_name;
}
public String getEmp_fname() {
return emp_fname;
}
public void setEmp_fname(String emp_fname) {
this.emp_fname = emp_fname;
}
public String getEmp_surname() {
return emp_surname;
}
public void setEmp_surname(String emp_surname) {
this.emp_surname = emp_surname;
}

@Override
public String toString(){
return emp_name;
}

}

use following where you want to perform database operations.

class EmpData{

public  Vector<EmployeeBean> getAllEmployees() throws SQLException{
String query = "SELECT emp_id, emp_name, emp_fname, emp_surname FROM employee";

Statement ps = null;
ResultSet rs = null;
Vector<EmployeeBean> vector = new Vector<EmployeeBean>();
try{
ps = (Statement)database.Mysqlstudent.con.createStatement();
rs = ps.executeQuery(query);
while(rs.next()){
EmployeeBean bean = new EmployeeBean();
bean.setEmp_id(rs.getInt("emp_id"));
bean.setEmp_name(rs.getString("emp_name"));
bean.setEmp_fname(rs.getString("emp_fname"));
bean.setEmp_surname(rs.getString("emp_surname"));
vector.add(bean);
}//end while loop
}finally{
if(ps != null) ps.close();
if(rs != null) rs.close();
}

return vector;

}//end getEmployees

}

and use it by creating a object of Empdata where we requires it. Like,

Empdata data = new Empdata();

Vector<EmployeeBean> vect = data.getAllEmployees();

so in vect variable you get all record of employees.

2 Comments

The new lambda expressions included in Java Platform Standard Edition 8 (Java SE 8).

Lambda expressions are a new and important feature included in Java SE 8. They provide a clear and concise way to represent one method interface using an expression. Lambda expressions also improve the Collection libraries making it easier to iterate through, filter, and extract data from a Collection. In addition, new concurrency features improve performance in multicore environments.

The following is a list of hardware and software requirements:

  • Java Development Kit (JDK 8) early access
  • NetBeans 7.4

Lambda Expression Syntax

Lambda expressions address the bulkiness of anonymous inner classes by converting five lines of code into a single statement. This simple horizontal solution solves the "vertical problem" presented by inner classes.

A lambda expression is composed of three parts.

Argument List Arrow Token Body
(int x, int y) -> x + y

The body can be either a single expression or a statement block. In the expression form, the body is simply evaluated and returned. In the block form, the body is evaluated like a method body and a return statement returns control to the caller of the anonymous method. The break and continue keywords are illegal at the top level, but are permitted within loops. If the body produces a result, every control path must return something or throw an exception.

Example

Here is how you write a Runnable using lambdas.

 6 public class RunnableTest {
 7   public static void main(String[] args) {
 8     
 9     System.out.println("=== RunnableTest ===");
10     
11     // Anonymous Runnable
12     Runnable r1 = new Runnable(){
13       
14       @Override
15       public void run(){
16         System.out.println("Hello world one!");
17       }
18     };
19     
20     // Lambda Runnable
21     Runnable r2 = () -> System.out.println("Hello world two!");
22     
23     // Run em!
24     r1.run();
25     r2.run();
26     
27   }
28 }

In both cases, notice that no parameter is passed and is returned. The Runnable lambda expression, which uses the block format, converts five lines of code into one statement.

Reference Source for this information is www.oracle.com

 

2 Comments

Java programming language support these primitive data types:

1. Byte : It is equals to 8 bits

2. Short : (16 bits equals to two bytes)

3. Int : (32 bits equals to 4 bytes)

4. Long : (64 bits equals to 8 bytes)

5. Boolean : Has to possible values either True or False

6. Char :Store a single char

7. Float : (32 bits equals to 4 bytes)

8. Double : (64 bits equals to 8 bytes)

All these data types considered as reserved keywords pre defined by programming language  . Primitive values cannot share its state with other primitive values. primitive data types are not object that why we do not use new keyword. There are default values for above types are:

default values

 

primitive data types

primitive data types

5 Comments

I am going to start with a basic description for java variables because variables in any language are very useful works as a building block for any program , so lets start...

First of all What is meaning of word variable it means not having a fixed pattern. Its a container hold a value for u ,  When we define a variable with value at beginning of  any program after some code we can change  value of that variable , of course there are lots of other benefits of variables in java ....so we will describe later.

A variable is also called field so do not confuse . In java we can define  variables as :

1. Instance variables

2. Class variables

3. Local variables

1. Instance variables : A variables which also called non static field define with out static keyword and value of instance variable are unique for each instance of a class.

Note : you can not use instance variable in static method till you can not create a object of that class having instance variable.

2. Class variables : A variable with static modifier and value of a static field is same in all over code and we use it by class name do not need to create object.

3. Local variablesA variable only visible to the method where they are declared , no any use of special keyword with local variables.

How we can use these variables:

first we have to define datatype then name of variable end with semicolon like:

int varA ;

now you can assign value to variable here e.g: int varA = 10; or you can assign value where ever you want in code. The advantage of java variable are that we can define and declare a variable any where in the code unlike C.

Working with variables

Working with variables