Collections

Question 1

List

Answer 1

Accepts duplicates, has an index number.

Question 2

ArrayList

Answer 2

retrieving is faster (Get) holds non-primitive data-types

Question 3

LinkedList

Answer 3

Add, addAll, remove, removeIf, retainAll.

Question 4

Vector

Answer 4

A synchronized version of ArrayList

Question 5

Stack

Answer 5

Syncronized version of arraylist With LIFO (last in first out) organization, pop() = LIFO

Question 6

Set

Answer 6

doesn’t accept duplicates, does not have an index

Question 7

HashSet

Answer 7

Random

Question 8

LinkedHash Set

Answer 8

keeps assertion order

Question 9

TreeSet

Answer 9

Ascending order doesn’t accept Null.

Question 10

Queue

Answer 10

Accepts duplicates, No index, FIFO (first in first out)

poll() = FIFO

Question 11

Iterable

Answer 11

Only for collections. Allows to properly remove objects.

Question 12

HashMap

Answer 12

Keys are in random order.

Question 13

LinkedHashMap

Answer 13

Insertion order

Question 14

TreeMap

Answer 14

Ascending order doesn’t accept Null

Question 15

HashTable

Answer 15

Keys are in random order, synchronized, does not accept null.

Question 16

Collections List Key Points

Answer 16

A list is an ordered collection of elements. Some languages call it a sequence or an array of varying lengths.

Question 17

Collections Set Key Points

Answer 17

A collection that contains no duplicate elements. Like a mathematical Set the interface denotes a collection that holds elements and basically answers a single question: is a given element contained in the set.

Doesn’t specify the order of elements when you iterate them, but all set implementations are created with the performance of the contains method in mind.

Two Implementations would be HashSet and TreeSet
HashSet: hashes the elements and distributes them into buckets by the hash value. Tree Set is backed by a balanced tree, which makes it ordered and navigable.

Typically use-cases for sets do not require navigating from element to element so the HashSet is the goto implementation you’ll tend to use.

Question 18

Collections Queue Key Points

Answer 18

a Queue is designed to hold elements prior to processing, the elements wait in line to be consumed and can be added to the tail of the queue.

Queues are those fundamental pieces of software that tie components together. IE: when components are communicating in a system, there’s typically a queue of messages sitting between them.

Queues are a special sort of collection as they mainly use the Queue interface, rather than methods inherited from the Collections Interface. IE: .offer / .poll / .peek