Top Most Interview Question Of Java Technology: June 2018

Saturday 9 June 2018

//create simple form using bootstrap and validate their field using java script..........

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>


<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">


<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>


<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>

<body>

<div class="container">
<h1 class="text-success text-center">User Registration Form</h1>
<div class="col-lg-8 m-auto d block">

<form action="#" onsubmit="return validation()" class="bg-light">
<div class="form-group">
<label>User Name:</label>
<input type="text" name="user" class="form-control" id="user" autocomplete="off">
<span id="username" class="text-danger font-weight-bold"></span>
</div>

<div class="form-group">
<label>Password:</label>
<input type="text" name="pass" class="form-control" id="pass" autocomplete="off">
<span id="password" class="text-danger font-weight-bold"></span>
</div>

<div class="form-group">
<label>Confirm Password:</label>
<input type="text" name="cnfpass" class="form-control" id="cnfpass" autocomplete="off">
<span id="cnfpassword" class="text-danger font-weight-bold"></span>
</div>

<div class="form-group">
<label>Mobile No:</label>
<input type="text" name="mobile" class="form-control" id="mobile" autocomplete="off">
<span id="mobileno" class="text-danger font-weight-bold"></span>
</div>
<div class="form-group">
<label>Email:</label>
<input type="text" name="email" class="form-control" id="email" autocomplete="off">
<span id="emailid" class="text-danger font-weight-bold"></span>
</div>
<input type="submit" name="submit" value="submit" class="btn btn-success">
</form>
</div>
</div>

<script type="text/javascript">
function validation() {

var user=document.getElementById('user').value;

var pass=document.getElementById('pass').value;

var cnfpass=document.getElementById('cnfpass').value;

var mobile=document.getElementById('mobile').value;

var email=document.getElementById('email').value;

if(user==' ')
{
document.getElementById('username').innerHTML="** please fill the User Name field";
//alert('required');
return false;
}

if(pass==' ')
{
document.getElementById('password').innerHTML="** please fill the Password field";
//alert('required');
return false;
}

if(cnfpass==' ')
{
document.getElementById('cnfpassword').innerHTML="** please fill the Confirm Password field";
//alert('required');
return false;
}

if(mobile==' ')
{
document.getElementById('mobileno').innerHTML="** please fill the mobile number field";
return false;
}

if(email==' ')
{
document.getElementById('emailid').innerHTML="** please fill the email field";
return false;
}

}

</script>

</body>
</html>

Sunday 3 June 2018

What is fail-fast, fail-safe and ConcurrentModificationException in java?

Iterator returned by few Collection framework Classes are fail-fast, means any structural modification made to these classes during iteration will throw ConcurrentModificationException in java.

Iterator returned by few Collection framework Classes are fail-safe, means any structural modification made to these classes during iteration won’t throw any Exception in java.

package javaresearch;

import java.util.List;

import java.util.ArrayList;

import java.util.Collections;

import java.util.Enumeration;

import java.util.Iterator;

import java.util.ListIterator;

public class ArrayListExample {

public static void main(String args[]) {

// creates array with initial capacity of 10.

List<String> arrayList= new ArrayList<String>();

arrayList.add("Govind");

arrayList.add("Ballabh");

// fail-fast

Iterator<String> iterator = arrayList.iterator();

while (iterator.hasNext()) {

arrayList.add("Khan"); // unComment to avoid ConcurrentModificationException

System.out.println(iterator.next());

}

// fail-fast

ListIterator<String> listIterator = arrayList.listIterator();

listIterator.next();

listIterator.previous();

while (listIterator.hasNext()) {

arrayList.add("Java"); // unComment to avoid ConcurrentModificationException

System.out.println(listIterator.next());

}

// fail-fast

Enumeration<String> listEnum = Collections.enumeration(arrayList);

while (listEnum.hasMoreElements()) {

arrayList.add("Technology"); // unComment to avoid ConcurrentModificationException

System.out.println(listEnum.nextElement());

}

//enhanced for loop is fail-fast

for (String string : arrayList) {

arrayList.add("Madhubani-Bihar"); // unComment to avoid ConcurrentModificationException

System.out.println(string);

}

package javaresearch;

import java.util.List;

import java.util.Collections;

import java.util.Enumeration;

import java.util.Iterator;

import java.util.ListIterator;

import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteArrayListExample {

public static void main(String args[]) {

// creates array with initial capacity of 10.

List<String> copyOnWriteArrayList = new CopyOnWriteArrayList<String>();

copyOnWriteArrayList.add("Govind");

copyOnWriteArrayList.add("Ballabh");

// fail-safe

Iterator<String> iterator = copyOnWriteArrayList.iterator();

while (iterator.hasNext()) {

copyOnWriteArrayList.add("Khan");

System.out.println(iterator.next());

}

System.out.println("-------------------------------------------------");

for (String string : copyOnWriteArrayList) {

System.out.println(string);

}

System.out.println("------------------------------------------");

// fail-safe

ListIterator<String> listIterator = copyOnWriteArrayList.listIterator();

// listIterator.next();

//listIterator.previous();

while (listIterator.hasNext()) {

copyOnWriteArrayList.add("Java");

System.out.println(listIterator.next());

}

System.out.println("------------------------------------------");

// fail-safe

Enumeration<String> listEnum = Collections

.enumeration(copyOnWriteArrayList);

while (listEnum.hasMoreElements()) {

copyOnWriteArrayList.add("Technology");

System.out.println(listEnum.nextElement());

}

System.out.println("------------------------------------------");

//enhanced for loop is fail-safe

for (String string : copyOnWriteArrayList) {

copyOnWriteArrayList.add("Madhubani-Bihar");

System.out.println(string);

}

o/p view:-----------------------

Govind

Ballabh

-------------------------------------------------

Govind

Ballabh

Khan

------------------------------------------

Govind

Ballabh

Khan

------------------------------------------

Govind

Ballabh

Khan

Java

------------------------------------------

Govind

Ballabh

Khan

Java

Technology

Saturday 2 June 2018

static block instance Block in java------------

Instance initialization block in java can be used to initialize instance variables in java.
Static initialization block in java can be used to initialize static variables in java.
==================================================================================

//Static block
Static blocks are also called Static initialization blocks in java.
Static block executes when class is loaded in java.
static blocks executes before instance blocks in java.
Only static variables can be accessed inside static block in java
static blocks can be used for initializing static variables or calling any static method in java.
this keyword cannot be used in static block in java.

======================================================================================
Instance blocks:-
Instance blocks are also called instance initialization blocks in java
Instance block executes when instance of class is created in java.
Also known as non-static initialization block in java.
instance blocks executes after static blocks in java.
Static and non-static variables (instance variables) can be accessed inside instance block in java.
instance blocks can be used for initializing instance variables or calling any instance method in java.
this keyword can be used in instance block in java.

========================================================================================

package javaresearch;

public class TestData {

static
{
System.out.println("Static Block");

}

public TestData()
{
System.out.println("Constructor");
}

{
System.out.println("Instance Block");
}

public static void main(String[] args) {
TestData td=new TestData();

}

}

============================================================================================

o/p-------------------------
Static Block
Instance Block
Constructor

============================================================================================

package javaresearch;

public class SuperClassDemo {

static
{
System.out.println("Super class static block");
}

{
System.out.println("Super class Instance block");
}

SuperClassDemo()
{
System.out.println("Super class Constructor");
}

}

================================================================================================

package javaresearch;

public class SubClassDemo extends SuperClassDemo
{

static
{
System.out.println("Sub class static block");
}

{
System.out.println("Sub class Instance block");
}

SubClassDemo()
{
System.out.println("Sub class Constructor");
}

public static void main(String[] args) {
SubClassDemo scd=new SubClassDemo();

}

}

============================================================================================

o/p:-------------------------
Super class static block
Sub class static block
Super class Instance block
Super class Constructor
Sub class Instance block
Sub class Constructor