InstanceOfJava

Jdbc Connction Steps with Examples

Posted by: Instanceofjava Posted date: 5:53 PM / comment : 0 JDBC

Example to connect to oracle database:

Connecting to java application to oracle database.you have to follow 5 steps :
1.load the driver class,
2.create the connection object,
3.create the statement object
4.execute query Connect
5.Connection close

oracle database connectivity steps:

Driver class:The oracle database driver class is oracle.jdbc.driver.OracleDriver.

Connection URl:The oracle database connection URL is jdbc:oracle:thin:@localhost:1521:xe.
here jdbc is API,oracle is the database, thin is the driver,local host is server on which oracle is running,or we can use IP address,1521 is port number and
and XE is the Oracle service name.

User name:The oracle database default userName is system.

Password:Password is given by the user at the time of installing the oracle database. In this example, we are going to use system123 as the password.


import java.sql.*; 

class ConnecttoOracle{ 

public static void main(String args[]){ 

try{ 

// load the driver class 

Class.forName("oracle.jdbc.driver.OracleDriver"); 



//create  the connection object 

Connection con=DriverManager.getConnection( 

"jdbc:oracle:thin:@localhost:1521:xe","system","oracle"); 



// create the statement object 

Statement stmt=con.createStatement(); 



// execute query 

ResultSet rs=stmt.executeQuery("select * from emp"); 

while(rs.next()) 

System.out.println(rs.getInt(1)+"  "+rs.getString(2)+"  "+rs.getString(3)); 



// close the connection object 

con.close(); 



}

catch(Exception e){

System.out.println(e);} 



} 

}

Example to connect to Mysql databaase:

Connecting to java application to mysql database.you have to follow 5 steps :
1.load the driver class,
2.create the connection object,
3.create the statement object
4.execute queryConnect
5.Connection close

Mysql database connectivity steps:

Driver class:The mysql database driver class is com.mysql.jdbc.Driver.

Connection URl:The mysql database connection URL is jdbc:mysql://localhost:3306/test.
here jdbc is API,mysql is database,local host is server on which mysql is running,or we can use IP address,3306 is port number and test is database name.
we can use any database name here.

Username:The mysql database default userName is root.

Password:Password is given by the user at the time of installing the mysql database. In this example, we are going to use root123 as the password.


import java.sql.*; 

class ConnecttoMysql{ 

public static void main(String args[]){ 

try{ 

class.forName("com.mysql.jdbc.Driver"); 



Connection con=DriverManager.getConnection( 

"jdbc:mysql://localhost:3306/database name","root","root123"); 



//here root is username and root123 is password 



Statement stmt=con.createStatement(); 



ResultSet rs=stmt.executeQuery("select * from emp"); 



while(rs.next()) 

System.out.println(rs.getInt(1)+"  "+rs.getString(2)+"  "+rs.getString(3)); 



con.close(); 



}

catch(Exception e){

System.out.println(e);} 



} 

    
}

Servlet example programs in eclipse

Posted by: Instanceofjava Posted date: 5:59 PM / comment : 0 Java EE , Servlets Tutorial

1.Run eclipse.File -> new -> dynamic web project

2. Give project name : example MyFirstApp and click on next

3. Please check Generate web.xml deployment descriptor to auto generate web.xml file

4.click on finish. now project structure will be created.

5.Go to webcontent and create a folder with name Jsp to place jsp files and create a index.jsp.

6. index.jsp will have an error because it is not having servlet jar. file so we need to include servler-apt.jar file.

now its fine. modify index.jsp with one text box and submit button.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org
/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login</title>
</head>
<body>
<form action="/MyFirstApp/hello" method="post">
Name:<input type="text" name="name" value="">
<input type="submit" name="name" value="submit">
</form>
</body>
</html>

7. create a servlet

package com.instanceofjava;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Hello extends HttpServlet{
private static final long serialVersionUID = 1L;
public void doPost(HttpServletRequest req, HttpServletResponse res) throws IOException,
ServletException{
String str= (String) req.getParameter("name");
req.setAttribute("name", str);
req.getRequestDispatcher("/Jsp/welcome.jsp").forward(req, res);
}
}

8. create a welcome.jsp page.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org
/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>welcome</title>
</head>
<body>
<%
String str=null;
try{
str=(String)request.getAttribute("name");
}catch(Exception e){
}
%>
<p>Welcome: <%=str %></p>
</body>
</html>

8. go to we.xml and include our servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns
/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>MyFirstApp</display-name>
<welcome-file-list>
<welcome-file>/Jsp/index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-class>com.instanceofjava.Hello</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app>

9. run the project , select tomcat 7 from apache.

10. Enter your name and click on submit.

Accessibility modifiers examples

Posted by: Instanceofjava Posted date: 8:49 PM / comment : 0 concept and program

The keywords which define accessibility permissions are called accessibility modifiers.
Java supports four accessibility modifiers to define accessibility permissions at different levels.

Accessibility modifier keywords:

1.private

2.protected

3.public

4.default(no keyword)

1.private:

The class members which have private keyword in its creation statement are called private members. Those members are only accessible within that class.
If we declare any variable or method with private accessibility modifier then those variables and methods are accessible only within that class , not accessible out side the class.

private variable are accessible within the class :

package com.instanceofjava;
public class PrivateDemo {
private String first_name;
private String last_name;
void show(){
System.out.println("First Name:="+first_name);
System.out.println("Last Name:="+last_name);
}
public static void main(String[] args) {
PrivateDemo obj= new PrivateDemo ();
obj.first_name="James";
obj.last_name="Goosling";
obj.show();
}
}

Output:

First Name:=James
Last Name:=Goosling

private variable are not accessible out side the class :

package com.instanceofjava;
public class PrivateDemo {
private String first_name;
private String last_name;
void show(){
System.out.println("First Name:="+first_name);
System.out.println("Last Name:="+last_name);
}
public static void main(String[] args) {
PrivateDemo obj= new PrivateDemo ();
obj.first_name="James";
obj.last_name="Goosling";
}
}

package instanceofjava;
class Demo {
public static void main(String[] args){
PrivateDemo obj= new PrivateDemo ();
obj.first_name="James"; // ERROR: The field PrivateDemo.first_name is not visible
}
}

private methods are accessible within the class :

package com.instanceofjava;
public class PrivateDemo {
private String first_name;
private String last_name;
private void show(){
System.out.println("First Name:="+first_name);
System.out.println("Last Name:="+last_name);
}
public static void main(String[] args) {
PrivateDemo obj= new PrivateDemo ();
obj.first_name="James";
obj.last_name="Goosling";
obj.show();
}
}

Output:

First Name:=James
Last Name:=Goosling

private variable are not accessible out side the class :

package com.instanceofjava;
public class PrivateDemo {
private String first_name;
private String last_name;
void show(){
System.out.println("First Name:="+first_name);
System.out.println("Last Name:="+last_name);
}
public static void main(String[] args) {
PrivateDemo obj= new PrivateDemo ();
obj.first_name="James";
obj.last_name="Goosling";
}
}

package instanceofjava;
class Demo {
public static void main(String[] args){
PrivateDemo obj= new PrivateDemo ();
obj.add(); // ERROR: The method add() from the type PrivateDemo is not visible
}
}

private variables and methods are accessible inside that class only. If we declare any variable or method as private , not accessible outside the class.

2.protected

The class members which have protected keyword in its creation statements are called protected members. Those members can be accessible with in package from all classes, but from out side package only in subclass that too using subclass name or its object.
protected variables accessible inside the package anywhere. Outside package accessible only in sub classes.

Same package anywhere:

package com.instanceofjava;
public class ProtectedDemo {
protected int a;
protected int b;
protected void show(){
System.out.println("a="+a);
System.out.println("b="+b);
}
public static void main(String[] args) {
ProtectedDemo obj= new ProtectedDemo ();
obj.a=12;
obj.b=13;
obj.show();
}
}

Output:

a=12
b=13

Different package subclass:

package com.accesiblitymodifiers;
public class Sample extends ProtectedDemo {
public static void main(String[] args) {
Sample obj= new Sample();
obj.a=12;
obj.b=13;
obj.show();
}
}

Output:

a=12
b=13

3.public

If we declare any variable or method with public access specifier then those members will be accessible to everywhere.

package com.instanceofjava;
public class PublicDemo {
public int x;
public int y;
public void show(){
System.out.println("x="+x);
System.out.println("y="+y);
}
public static void main(String[] args) {
PublicDemo obj= new PublicDemo ();
obj.x=1;
obj.y=2;
obj.show();
}
}

Output:

4.default

If we declare any member with no keyword those members are called default members.
default members are accessible to package level.
Means we can access anywhere in same package but we can not access in out side the package under any condition.
So default will acts as public inside package and private out side the package.

Java data types with examples

Posted by: Instanceofjava Posted date: 4:18 PM / comment : 0 concept and program

In java mainly we have two types of data types.

Primitive data types or Fundamental data types.
Referenced data types or Derived data types.

1.Primitive Data types

1.byte

package com.instanceofjava;
public class ByteDemo {
public static void main(String[] args) {
byte a=10; // a is a variable of type byte holding the value 1;
byte b=20;// b is a variable of type byte holding the value 2;
byte c= (byte)(a+b);
System.out.println(c);
}
}

Output:

2.short

package com.instanceofjava;
public class ShortDemo {
public static void main(String[] args) {
short a=1;
short b=2;
short c= (short)(a+b);
System.out.println(c);
}
}

Output:

3.int

package com.instanceofjava;
public class IntDemo {
public static void main(String[] args) {
int a=10; // a is a variable of type integer holding the value 10;
int b=20;// b is a variable of type integer holding the value 20;
int c= a+b;
System.out.println(c);
}
}

Output:

4.long

package com.instanceofjava;
public class LongDemo {
public static void main(String[] args) {
long a=1234567890;
long b=1234567890;
long c= a+b;
System.out.println(c);
}
}

Output:

2469135780

5.float

package com.instanceofjava;
public class FloatDemo {
public static void main(String[] args) {
float a=1234567.8f;
float b=1234567.8f;
float c= a+b;
System.out.println(c);
}
}

Output:

2469135.5

7.double

package com.instanceofjava;
public class DoubleDemo {
public static void main(String[] args) {
double a=1234567910112181314151634444422233334491.1d;
double b=1234567910112181314151634444422233334491.8d;
double c= a+b;
System.out.println(c);
}
}

Output:

2.4691358202243627E39

8.char

package com.instanceofjava;
public class CharDemo {
public static void main(String[] args) {
char a='A';
char b= 'B';
System.out.println(a);
System.out.println(b);
System.out.println(a+b);
}
}

Output:

9.boolean

package com.instanceofjava;
public class BooleanDemo {
public static void main(String[] args) {
boolean a=true;
boolean b= false;
System.out.println(a);
System.out.println(b);
}
}

Output:

true
false

1.Referenced Data types

1.class

package com.instanceofjava;
public class Sample{
int a,b;
void add(){
System.out.println(a+b);
}
public static void main(String[] args) {
Sample obj= new Sample();
obj.a=10;
obj.b=12;
obj.add();
}
}

Output:

2.Array

package com.instanceofjava;
public class ArrayDemo {
public static void main(String[] args) {
int a[]={1,2,3,4,5,6};
for (int i = 0; i < a.length; i++) {
System.out.println(a[i]);
}
}
}

Output:

Constructors in java

Posted by: Instanceofjava Posted date: 5:25 PM / comment : 0 concept and program

Constructors will be executed when the object is created.
Constructors should have same name of class name.
Executed once per object.
Basically used to assign instance variables
We can overload constructors.
We can call super class constructor form sub class constructor.

package instanceofjava;
class A{
A(){
}
}
}

while creating object constructor will be executed so we can assign instance variables to some default values.

package instanceofjava;
class A{
int a,b
A(int x, int y){
a=x;
b=y;
}
public static void main(String[] args){
A a=new A(10,20);
}
}

Types of constructors:

There are two types of constructors
Default constructors
Parameterized constructor.

Default constructor:

Default constructor will not have any arguments.
If we not defined any constructor in our class. JVM automatically defines a default constructor to our class.

package instanceofjava;
class Sample{
int a,b
Sample(){
a=37;
b=46;
}
public static void main(String[] args){
Sample obj=new Sample();
System.out.println(obj.a);
System.out.println(obj.b);
}
}

Output:

Parameterized constructor

package instanceofjava;
class Sample{
int a,b
Sample(int x, int y){
a=x;
b=y;
}
public static void main(String[] args){
Sample obj=new Sample(37,46);
System.out.println(obj.a);
System.out.println(obj.b);
}
}

Output:

Constructor overloading:

package instanceofjava;
class Sample{
int a,b
Sample(){
this(1,2);
System.out.println("Default constructor");
}
Sample(int x , int y){
this(1,2,3);
a=x;
b=y;
System.out.println("Two argument constructor");
}
Sample(int a , int b,int c){
System.out.println("Three argument constructor")
}
public static void main(String[] args){
Sample obj=new Sample();
System.out.println(obj.a);
System.out.println(obj.b);
}
}

Output:

Three argument constructor
Two argument constructor
Default argument constructor
1
2

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Top 15 Garbage Collection Interview Questions

1.What is Garbage Collection in Java?

2.How JVM can destroy unreferenced object?

3.So can you guarantee objects destruction?

4.Can we force garbage collector?

5.How can we request JVM to start garbage collection process?

6.What is the algorithm JVM internally uses for destroying objects?

7.Which part of the memory is involved in Garbage Collection?

8.What is responsibility of Garbage Collector?

9. When does an object become eligible for garbage collection?

10. What are the different ways to make an object eligible for garbage collection when it is no longer needed?

11.What is purpose of overriding finalize() method?

12.How many times does the garbage collector calls the finalize() method for an object?

13.What happens if an uncaught exception is thrown from during the execution of finalize() method of an object?

14.What are the different ways to call garbage collector?

15. How to enable /disable call of finalize() method of exit of application?

Jdbc Connction Steps with Examples

Servlet example programs in eclipse

Accessibility modifiers examples

Accessibility modifier keywords:

1.private

2.protected

3.public

4.default(no keyword)

1.private:

private variable are accessible within the class :

Output:

private variable are not accessible out side the class :

private methods are accessible within the class :

Output:

private variable are not accessible out side the class :

2.protected

Same package anywhere:

Output:

Different package subclass:

Output:

3.public

Output:

4.default

Java data types with examples

1.Primitive Data types

1.byte

Output:

2.short

Output:

3.int

Output:

4.long

Output:

5.float

Output:

7.double

Output:

8.char

Output:

9.boolean

Output:

1.Referenced Data types

1.class

Output:

2.Array

Output:

Constructors in java

Types of constructors:

Default constructor:

Output:

Parameterized constructor

Output:

Constructor overloading:

Output: