Techno Interview

Collection

COURSES

04 Month
DURATION

01 Hours

Collection is combination of different type of objects in a single entity.
Ex- group of different type of book in library

Difference between Collection and Collections in Java?

Collection	Collections
Collection is an interface	Collections is utility class
public interface Collection extends Iterable	public class Collections extends Object
The important methods of Collection interface are add() remove() size() clear()	Collections class contains only static methods like sort() min() max() fill() copy() reverse()
It is used to store list of object in a single object	It is used to operate on collection.

Difference between List and Set?

List	Set
List is child interface of collection interface	Set is also a child interface of Collection interface
List allows duplicate	Set does not allow duplicate
List allows multiple null values	Set allow only one null value
List maintain the insertion order	Set does not maintain the insertion order

Difference between Array and ArrayList?

Array	ArrayList
Array is fixed in size	ArrayList is growable by nature.
Array support only homogenous data	ArrayList support both homogenous and heterogenous data
Array is not good for memory management	ArrayList save memory
Array is faster in execution	ArrayList is slower in execution

what are generics in java?

Generics is used to convert heterogenous datatype to homogenous datatype. generics force the java programmer to store a specific type of objects.
Generics is a part of collection interface, it used to specify the type of data either string or integer and specific wrapper class is used for it

Difference between ArrayList and LinkedList?

ArrayList	LinkedList
ArrayList is implementation of dynamic array	LinkedList is an implementation of doubly LinkedList
ArrayList is list based structure.	LinkedList is node-based structure
ArrayList initial capacity is 10	Linked List Constructs empty list
ArrayList increases its size by 50%	LinkedList increases its size by doubling its size
ArrayList is good for data retrieval i.e. insertion and deletion	LinkedList is good for data manipulation such as sorting and searching
ArrayList provides random access of data	LinkedList does not allowed random access of data
ArrayList is slower	LinkedList is faster in execution

Difference Between ArrayList and Vector?

ArrayList	Vector
part of JDK 1.2	part of 1.0 JDK
ArrayList does not belongs to Legacy	Vector belongs to Legacy classes
ArrayList is not synchronized and non threadsafe i.e. not good for threaded application	vector is threadsafe and Synchronized i.e. good for threaded application
ArrayList increases its size by 50%	Vector increases its size by 100%

Difference between HashSet and Linked HashSet?

HashSet	Linked HashSet
HashSet belongs to 1.2 JDK	Linked HashSet belongs to 1.4 JDK
HashSet require less memory	It requires more memory than HashSet.
It provides slightly faster performance than LinkedHashSet	It provides low performance than HashSet
HashSet does not maintain insertion order	Linked HashSet maintain insertion order

Difference between HashSet and TreeSet?

HashSet	TreeSet
HashSet is implementation of HashTable	TreeSet is implementation of Tree Structure
HashSet has time complexity of O(n)	TreeSet has time complexity of O(log n)
HashSet does not maintain any order	TreeSet maintain ascending order
HashSet is faster in execution	TreeSet is slower in execution
HashSet use hashcode and equal method	TreeSet use compare and CompareTo() method

HashMap

HashMap is part of map interface ,follow key and value pair

How HashMap works internally?

HashMap works internally on hashing principle. which internally generates the hashcode
.when put method is called it will check the value of key if key value is null
it will store at zero index. After that index value is calculated for hashcode
by index= hashcode(key)& (n-1) formula. Once the node value is calculated it followed LinkedList structure
which compares the hashcode value and equal method check the key value if hashcode is same but different key.
it will store in same bucket with same index value but different value,
but in the case of collision if both values are same for key
then value will be overridden by new value itself.

Difference between HashMap and HashTable?

HashTable	HashMap
Implementation of dictionary classes	Implementation of linked HashMap
HashTable is synchronized and threadsafe	HashMap is non synchronized and non threadsafe
Slow in the execution	Faster in the execution
HashTable does not allow null value for key	HashMap allow one null key

Difference between HashMap and Linked HashMap?

HashMap	Linked HashMap
HashMap is part of jdk 1.2	Linked HashMap is part of jdk 1.4
HashMap is implementation of map interface	Linked HashMap is an implementation of HashMap
HashMap is allowed single null key	Linked HashMap does not allow null key
HashMap is slower in terms of execution	Linked HashMap is faster in execution

Difference between HashMap and Concurrent HashMap?

HashMap	Concurrent HashMap
HashMap is part of jdk 1.2	Concurrent HashMap is part of jdk 1.5
Non synchronized and threadsafe	It is thread safe and synchronized
Not good for threaded application	Good for threaded application
Allow one null key	Does not allow null key value
Faster wrt concurrent HashMap	Slower in terms of execution

Difference between HashMap and TreeMap?

HashMap	TreeMap
HashMap follow map structure	TreeMap follow tree structure
HashMap is unordered structure	TreeMap follow ascending order
HashMap have time complexity of O(n)	TreeMap have a complexity of O(log n)
Hash map allow one null key	TreeMap does not allow null key
HashMap is non synchronized and non threadsafe	TreeMap is synchronized and threadsafe
HashMap is faster in execution	TreeMap is slower in execution

Difference between Comparable and Comparator?

Comparable	Comparator
Compare the value in default shorting order	Compare the value in customized manner
Part of java.lang package	Part of java.util package
Compare and equal are part of it	compareTo method is used
String and wrapper class using it	used by collectors or rule-based collectors.

Difference between Iterator and List Iterator?

Iterator	List Iterator
Allowed implementation in forward direction or Unidirectional	Allowed implementation in both direction i.e. forward and backward or bidirectional.
Used for list, set and Map	Used for list only
Single side implements at one time	both side implementation possible at a same time

Difference between Queue and Stack?

Queue	Stack
Queues are based on the FIFO principle	Stacks are based on the LIFO principle
Insertion and deletion in queues takes place from the opposite ends of the list. The insertion takes place at the rear of the list and the deletion takes place from the front of the list.	Insertion and deletion in stacks takes place only from one end of the list called the top.
Insert operation is called enqueue operation	Insert operation is called push operation.
Delete operation is called dequeue operation.	Delete operation is called pop operation.
Queue is used in solving problems having sequential processing	Stack is used in solving problems works on recursion.