Selenium Interview Questions

Friends below are some interview questions you might be asked . If you get familiar with these you can crack interview

Java basics for Freshers - Just try to understand Highlighted In red Selenium related question I will update in this blog. These are the question are asked when I take an interview . Remenber if you can crack basic Java question you interview will be easy

for experience All questions are relavent

Q6 what is the difference between List and Set?

Set	List
Set allows only unique elements	List allows duplicate elements
Set is unordered while List is ordered	List maintains the order in which the objects are added

Q7 what is the difference between Map and Set?

Set	Map
Set contains unique keys but does not allow duplicate values	Map contains unique key but allows duplicate values

Q8 what are the classes implementing List and Set interface?

List	Set
ArrayList, Vector, Linked List	HashSet, Tree Set

Q9 what is an iterator?
Iterator is an interface. It is found in java.util package. It provides methods to iterate over any Collection.

Q10 what is the difference between Iterator and Enumeration?

Iterator	Enumeration
Iterator you can remove element(allows read/write operations)	Doesn’t support remove(supports readonly operations)

Q12 which methods you need to override to use any object as key in HashMap?

To use any object as key in HashMap, it needs to implement equals() and hashCode() method 

What it static key word : **this is important most interview this questions will be asked****

Answer

1. the variable or method declared as static can be directly called using call name

2. Any block of code that needs to executed before main method you put that code in static block

static{

your code goes here, this block of code will be exe used before main method starts execution

}

static main ()

Q13 what is the difference between Queue and Stack?

Queue	Stack
First In First out	Last In First Out

Q14 How to reverse the List in Collections?

Collections.reverse(listobject);

Q15 How to convert the array of strings into the list?

asList() 

Q16 what is the difference between ArrayList and Vector?

Vector	ArrayList
Vector is Synchronized	Array List is not synchronized
Vector is slow	ArrayList is fast
Vector increases the capacity twice of its initial size	ArrayList increases its ArraySize by 50%
Vector supports both Enumeration and Iterator	Array List support only Iterator for traversing

Q17 what is the difference between HashMap and Hashtable? - This is must

Commenly asked interview question

HashMap	Hashtable
HashMap allows null key value insertion	Hashtable does not allow null keys and null values.
HashMap is not synchronized or thread-safe	Hashtable is synchronized or thread-safe.

Q20 what is the difference between Array and ArrayList in Java? ** Very 

important for sure you will be asked

Array	ArrayList
Array is static in size	ArrayList is dynamic in size.
Array can contain primitive data types	ArrayList cannot contain primitive data types. If declared primitive data type JVM through Auto boxing(converting primitives to equivalent objects internally)
Fast performance	Slow performance
does not guarantee ordered  elements.	does not guarantee ordered  elements.

Hashing: How Hash Map Works In Java Or How Get() Method Works Internally

HashMap works on the principle of Hashing.  To understand Hashing, we should understand the three terms first   i.e  Hash Function , Hash Value and Bucket .

HashMap get(Key k) method calls hashCode method on the key object and applies returned hashValue to its own static hash function to find a bucket location(backing array) where keys and values are stored in form of a nested class called Entry (Map.Entry)

ArrayList	Linked list
Manipulation with ArrayList is slow	Manipulation with LinkedList is faster
Ddataccess is faster.Better performance becaue of Index based search	Data access is slower. Performance is slower As Linked list inherits Double Linked list which requires the traversal through all the elements for searching an element.
One should go for Arraylist implemententation when there are more get calls

Comparator

Is an interface which is used for sorting objects in Java.

Compare to method

Comparable	Comparator
Comparable provides single sorting sequence. In other words, we can sort the collection on the basis of single element such as id or name or price etc.	Comparator provides multiple sorting sequence. In other words, we can sort the collection on the basis of multiple elements such as id, name and price etc.
Comparable affects the original class i.e. actual class is modified.	Comparator doesn't affect the original class i.e. actual class is not modified.
Comparable is found in java.lang package.	Comparator is found in java.util package.
We can sort the list elements of Comparable type byCollections.sort(List) method.	We can sort the list elements of Comparator type byCollections.sort(List,Comparator) method.

HashSet vs TreeSet

HashSet	TreeSet
Removes duplicates	Removes duplicates
Don’t sort element	Sorts elements in Ascending order

Iterator vs List Iterator

Iterator	List Iterator
Iterator is used for traversing List and Set both.	We can use List Iterator to traverse List only, we cannot traverse Set using ListIterator.
We can traverse in only forward direction using Iterator.	Using ListIterator, we can traverse a List in both the directions (forward and Backward)

HashMap vs TreeMap

HashMap	Tree Map
Return elements as it on how they are added	Return Sorted in Ascending order of Keys

HashMap vs tree map

Binary tree

Enums

Hash map usage

• Create an entry set
• Create a iterator object over entry set
• Then iterate

LinkedHashMap

Same as HashMap just preserves the insertion order

What are concurrentCollectionClasses? 

In jdk1.5 , Java Api developers had introduced new package called java.util.concurrent that have thread-safe collection classes as they allow collections to be modified while iterating

Ex : Concurrent Hash Map class

How will you make Collections readOnly ?

Collections.unmodifiableMap(Map m)

Collections.unmodifiableList(List l)

Collections.unmodifiableSet(Set s)

Difference between Stack vs Heap in Java

Stack	Heap
Stack memory is used to store variables and functions	Heap memory is used to store Objects

What is reflection?

The ability to examine or modify the runtime behaviour of applications running in the Java virtual machine

• Examine an object's class at runtime
• Construct an object for a class at runtime
• Examine a class's field and method at runtime
• Invoke any method of an object at runtime
• Change accessibility flag of Constructor, Method and Field

Binary Tree

A binary tree is a tree data structure in which each node has at most two children, which are referred to as the left child and the right child
PreOrder traversal - In PreOrder traversal, each node is processed before either of its sub-trees. In simpler words, Visit each node before its children.

InOrder traversal : In In-Order traversal, each node is processed between subtrees.In simpler words,Visit left subtree, node and then right subtree.

PostOrder traversal: In PostOrder traversal,each node is processed after subtrees traversal. In simpler words, Visit left subtree,  right subtree and then node.

Level order traversal : In Level order traversal, tree is traversed by each level. It is same as breadth first search.

Spiral/Zigzag order traversal : In spiral order traversal, tree is traversed in spiral shape. 

Binary Search

Binary search is a fast search algorithm. This search algorithm works on the principle of divide and conquer. For this algorithm to work properly the data collection should be in sorted form.

Binary search a particular item by comparing the middle most item of the collection. If match occurs then index of item is returned. If middle item is greater than item then item is searched in sub-array to the right of the middle.

What is immutable class in Java?

Immutable classes are those class, whose object cannot be modified once created. Immutable and mutable objects are, String and StringBuffer.

Class can be made immutable by making it Final.
Benefits

• Thread Safe

Stack

Stack is a subclass of Vector collection

Push pop

Sorting

Bubble Sort

Comparing each pair of adjacent items and swapping them

Selection Sort

Tries to identify the smallest and the largest elements and swapping the positions

Insertion Sortd

Quick sort in java.

Quicksort or partition-exchange sort, is a fast sorting algorithm, which is using divide and algorithm. Quicksort first divides a large list into two smaller sub-lists: the low elements and the high elements. Quicksort can then recursively sort the sub-lists.

Merge sort in java.

Divided into unsorted n no of patterns and

What is difference between Singly Linked List and Doubly Linked List data structure?
Main difference between singly linked list and doubly linked list is ability to traverse. In a single linked list, node only points towards next node, and there is no pointer to previous node, which means you cannot traverse back on a singly linked list. On the other hand doubly linked list maintains two pointers, towards next and previous node, which allows you to navigate in both direction in any linked list.

Difference between ArrayList and LinkedList:

ArrayList	LinkedList
1) ArrayList internally uses dynamic array to store the elements.	LinkedList internally uses doubly linked list to store the elements.
2) Manipulation with ArrayList is slow because it internally uses array. If any element is removed from the array, all the bits are shifted in memory.	Manipulation with LinkedList is faster than ArrayList because it uses doubly linked list so no bit shifting is required in memory.
3) ArrayList class can act as a list only because it implements List only.	LinkedList class can act as a list and queue both because it implements List and Deque interfaces.
4) ArrayList is better for storing and accessing data.	LinkedList is better for manipulating data.

Thread.sleep vs  Thread.wait vs Thread.Yield

Thread.sleep cannot be revoked

Thread.wait can notify thread to continue

Thread.yieid will go to runnable/ ready state

Thread.Wait releases the monitor or lock it was holding on that object, but when a thread calls the sleep() method, it never releases the monitor even if it is holding. 

Thread.yield() method pauses the currently executing thread temporarily for giving a chance to the remaining waiting threads of the same priority to execute. If there is no waiting thread or all the waiting threads have a lower priority then the same thread will continue its execution

Volatile

Any way the volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache value of this variable and always read it from main memory. ...Java volatile keyword cannot be used with method or class and it can only be used with variable.

So if you want to share any variable in which read and write operation is atomic by implementation e.g. read and write in an int or a boolean variable then  you can declare them as volatile variable.