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Minggu, 19 Juni 2016

Javascript interview questions

Validate email address using javascript

Kris Kimcil 05.52 Komentar

One of the famous interview question in JavaScript : how to validate email address in JavaScript.
In order to validate a text field of HTML we need a JavaScript function.
On submit form we need to call a java script function to validate all fields in the form also known as client side validation.
Now on form submit we need to check email text field and validate it whether entered email is in correct format or not for ex: instanceofjava@gmail.com.

JavaScript program for email validation:

<!DOCTYPE html>
<html>
<head>
<script>
function validateEmailForm() {
var x = document.forms["Form_Name"]["txt_email"].value;
var atpos = x.indexOf("@");
var dotpos = x.lastIndexOf(".");
if (atpos<1 || dotpos<atpos+2 || dotpos+2>=x.length) {
alert("Not a valid e-mail address");
return false;
}
}
</script>
</head>
<body>
<form name="Form_Name" action="User_email_validation.jsp" onsubmit="return
validateEmailForm();" method="post">
Email: <input type="text" name="txt_email">
<input type="submit" value="Submit">
</form>
</body>
</html>

Validate email in java-script using regular expression: on submit form validation

<!DOCTYPE html>
<html>
<head>
<script>
function validateEmailForm() {
var email = document.forms["Form_Name"]["txt_email"].value;
var re = /\S+@\S+\.\S+/;
return re.test(email);
}
}
</script>
</head>
<body>
<form name="Form_Name" action="User_email_validation.jsp" onsubmit="return
validateEmailForm();" method="post">
Email: <input type="text" name="txt_email">
<input type="submit" value="Submit">
</form>
</body>
</html>

HTML 5 Email validation:

<form>
<input type="email" placeholder="Enter your email">
<input type="submit" value="Submit">
</form>

email address validation code in java script

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Core java Interview Questions

Java XML parsing using DOM parser

Kris Kimcil 04.28 Komentar

Employees.xml:

Employee.java

package javaXMLParsing;
public class Employee {
String id;
String firstName;
String lastName;
String location;
@Override
public String toString() {
return firstName+" "+lastName+"("+id+")"+location;
}
}

Java Example program to parse XML using DOM parser:

DOMParserDemo.java

package javaXMLParsing;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class DOMParserDemo {
public static void main(String[] args) throws Exception {
//Create object of DOM Builder Factory class By using
//DocumentBuilderFactory.newInstance() method
DocumentBuilderFactory factoryobj =
DocumentBuilderFactory.newInstance();
//Create DOM Builder Object from DocumentBuilderFactory object
DocumentBuilder builder = factoryobj.newDocumentBuilder();
//Load the XML document and parse it
Document documentobj =
builder.parse(
ClassLoader.getSystemResourceAsStream("javaXMLParsing/Employee.xml"));
List<Employee> empList = new ArrayList<>();
//Iterating through the nodes and extracting the data.
NodeList nodeList = documentobj.getDocumentElement().getChildNodes();
for (int i = 0; i < nodeList.getLength(); i++) {
//We have encountered an <employee> tag.
Node node = nodeList.item(i);
if (node instanceof Element) {
Employee emp = new Employee();
emp.id = node.getAttributes().
getNamedItem("id").getNodeValue();
NodeList childNodes = node.getChildNodes();
for (int j = 0; j < childNodes.getLength(); j++) {
Node cNode = childNodes.item(j);
//Identifying the child tag of employee every employee .
if (cNode instanceof Element) {
String content = cNode.getLastChild().
getTextContent().trim();
switch (cNode.getNodeName()) {
case "firstName":
emp.firstName = content;
break;
case "lastName":
emp.lastName = content;
break;
case "location":
emp.location = content;
break;
}
}
}
empList.add(emp);
}
}
//Printing the Employee list by using for each loop.
for (Employee emp : empList) {
System.out.println(emp);
}
}
}

Output:

saidesh kilaru(001)Bangalore
ajay chanukya(002)Chicago
Vinod Gandrakoti(003)Hyderabad

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Sabtu, 18 Juni 2016

Difference between Collections and Collection in java with example program

Kris Kimcil 09.07 1 Komentar

Famous java interview question: difference between collections and collection in java
Major difference between Collection and Collections is Collection is an interface and Collections is a class.
Both are belongs to java.util package
Collection is base interface for list set and queue.
Collections is a class and it is called utility class.
Collections utility class contains some predefined methods so that we can use while working with Collection type of classes(treeset, arraylist, linkedlist etc.)
Collection is base interface for List , Set and Queue.

Collection vs Collections

public interface Collection<E>
extends Iterable<E>

public class Collections
extends Object

difference between collections and collection in java

Collections utility class contains static utility methods so that we can use those methods by using class name without creating object of Collections class object
Lest see some methods of Collections class.

addAll: public static <T> boolean addAll(Collection<? super T> c,T... elements)
reverseOrder: public static <T> Comparator<T> reverseOrder()
shuffle: public static void shuffle(List<?> list)
sort:public static <T extends Comparable<? super T>> void sort(List<T> list)

How to Relate Collection and Collections

ArrayList is a Collection type of class means it is implementing Collection interface internally
Now lets see a java example program to sort ArrayList of elements using Collections.sort() method.

public class ArrayList<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, Serializable

1.Basic Java example program to sort arraylist of integers using Collections.sort() method

package com.javasortarraylistofobjects;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
public class SortArrayListExample{
public static void main(String[] args) {
//create an ArrayList object
ArrayList<Integer> arrayList = new ArrayList<Integer>();
//Add elements to Arraylist
arrayList.add(10);
arrayList.add(7);
arrayList.add(11);
arrayList.add(4);
arrayList.add(9);
arrayList.add(6);
arrayList.add(2);
arrayList.add(8);
arrayList.add(5);
arrayList.add(1);
System.out.println("Before sorting ArrayList ...");
Iterator itr=arrayList.iterator();
while (itr.hasNext()) {
System.out.println(itr.next());
}
/*
To sort an ArrayList object, use Collection.sort method. This is a
static method. It sorts an ArrayList object's elements into ascending order.
*/
Collections.sort(arrayList);
System.out.println("After sorting ArrayList ...");
Iterator itr1=arrayList.iterator();
while (itr1.hasNext()) {
System.out.println(itr1.next());
}
}
}

Output:

Before sorting ArrayList ...
10
7
11
4
9
6
2
8
5
1
After sorting ArrayList ...
1
2
4
5
6
7
8
9
10
11

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Basic Java Example programs Core java Interview Questions

Java Program to find missing numbers in an array

Kris Kimcil 07.54 Komentar

To find missing numbers in an array first we need to make sure that array is sorted.
After sorting we need to check that array each element with next element then we can find the difference.
if Array is not sorted :To sort array use Arrays.sort(array);
If difference is 1 then no need to do any thing because numbers are in order.
If difference is not equal to 1 then we need to print all those numbers or pick those numbers and place it in one array.
this would be the logic to find missing numbers in an array
Here there may be a chance of array not starts with 1 then we need to check first itself whether array starts with 1 or not if not we need to print 1 to starting element of array.
for example int a[]={4,5,6,8}; then we need to print 1 2 3 7.

Lets see a java example program to find missing numbers in an array.

package arraysInterviewQuestions;
public class PrintMissingNumbers {
private static void findMissingNumber(int[] number){
// take max length as last number in array
int k[] = new int[number[number.length-1]];
int m=0;
if(number[0]!=1){
for (int x = 1; x < number[0]; x++) {
k[m] = x;
m++;
}
}
for (int i = 0; i < number.length -1; i++) {
int j = i+1;
int difference = number[j] - number[i] ;
if(difference != 1 ){
for (int x = 1; x < difference; x++) {
k[m] = number[i] + x;
m++;
}
}
}
System.out.println("missing numbers in array ::");
for (int l = 0; l < m ; l++) {
System.out.println( k[l]+" ");
}
}
public static void main(String[] args) {
int a[]= {2,4,6,9,10,20};
//if Array is not sorted :To sort array use Arrays.sort(a);
findMissingNumber(a);
}
}

program to find missing number in an array in java

Change the array in main method and practice try to find missing elements in an array that contains 1 to 100 numbers.

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Jumat, 17 Juni 2016

Core java Interview Questions

Dynamic polymorphism in java with example program

Kris Kimcil 11.53 Komentar

Polymorphism means defining multiple methods with same name.

Two types of polymorphism
1.Static polymorphism
2.Dynamic polymorphism.

Static polymorphism:

Defining multiple methods with same name and with different type of arguments is known as static polymorphism.
We can achieve this static polymorphism using method overloading.

Static polymorphism in java with example program

package com.instanceofjava;
class A{
public void show(int a){
System.out.println("saidesh");
}
public void show(int a,int b){
System.out.println("ajay");
}
public void show(float a){
System.out.println("vinod");
}
public static void main(String args[]){
A a=new A();
a.show(10);
a.show(1,2);
a.show(1.2);
}
}

Output:

saidesh
ajay
vinod

Dynamic polymorphism:

Defining multiple methods with same name and with same signature in super class and sub class.
We can achieve dynamic polymorphism by using method overriding concept in java.
Define a method in super class and override same method with same signature in sub class
Whenever we call the method on t the object based on the object corresponding class method will be executed dynamically.

Java example program on dynamic polymorphism: (Real time example)

package MethodOverridingExamplePrograms;
public class Vehicle{
void Start(){
System.out.println("Vehicle started")
}
}

package MethodOverridingExamplePrograms;
public class Car extends Vehicle{
void Start(){
System.out.println("Car started")
}
}

package MethodOverridingExamplePrograms;
public class Bus extends Vehicle{
void Start(){
System.out.println("Bus started")
}
}

package MethodOverridingExamplePrograms;
public class Bike extends Vehicle{
void Start(){
System.out.println("Bike started")
}
}

package MethodOverridingExamplePrograms;
public class Test{
public static void startVehicle(Vehicle vh){
vh.start();
}
}

Dynamic polymorphism in java with example program

In the above example based on the object creation at run time corresponding class method will be executed.

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Jumat, 10 Juni 2016

Core java Interview Questions java interview programs

toString() method in java with example program

Kris Kimcil 21.53 Komentar

toString() method belongs to object class.
By default it will be called once whenever we try to print object.
toString() method by default will print classname@hex representation of hashcode.
We can override this toString() method from object class.

public String toString(){
return null;
}

Advantage of toString() method in java.

When ever we try to print object by default toString() method will be called and print classname@HEX_hashcode.
We can represent object in String format using toString() method.
if we want to represent string representation of object then we need to override toString() method in our class and return values of the object as a String.

Java example program to print object without using toString() method.

Lets see an example program on printing object of a class.

package tostringexamples;
public class ToStringDemo {
int a,b;
ToStringDemo(int x, int y){
a=x;
b=y;
}
public static void main(String[] args) {
ToStringDemo obj= new ToStringDemo(1,2);
ToStringDemo obj2= new ToStringDemo(3,4);
System.out.println(obj);
System.out.println(obj2);
}
}

Output:

tostringexamples.ToStringDemo@2a139a55
tostringexamples.ToStringDemo@15db9742

In the above program when we print object of ToStringDemo class it prints ToStringDemo@2a139a55.
It means when ever we print object of the class toString() method will be called and by default toString() method print classname@HEX_hashcode.
To test this now we will override the toString() method and prints object of the class and if it calls our method then we can understand that when ever we print object by default toString() method will be called.

Java example program to print object by overriding toString() method.