Collection

Question 1

Give a short description of the interface: Iterable

Answer 1

a class implementing this interface can be used for iterating with a foreach statement

Question 2

Give a short description of the interface : Collection

Answer 2

Common base interface for classes in the collection hierarchy. When you want to write methods that are very general, you can pass Collection interface.

Most important methods:
boolean add(Element elem)
void clear()
boolean isEmpty()
Iterator iterator()
boolean remove(Object obj)
int size()
Object[] toArray()

Question 3

Give a short description of the interface : List

Answer 3

• Base interface for containers that store a sequence of elements.
• You can access the elements using an index.
  Maintains insertion order
• Can store duplicates

Question 4

Give a short description of the interface : Set, SortedSet, NavigableSet

Answer 4

• interfaces for containers that dont allow duplicates
• SortedSet maintains the set elements in a sorted order
• NavigableSet allows searching the set for the closest match

Question 5

Give a short description of the interface : Map, SortedMap, NavigableMap

Answer 5

interfaces for containers that map keys to values. In sortedMap, the keys are sorted in order

• NavigableMap allows you to search and return the colest match for given search
• Map hierarchy does NOT extend Collection interface

Question 6

Give a short description of the interface: Queue, Deque

Answer 6

Queue interface is a base interface for containers that hold a sequence of elements for processing.
For ex. the classes implementing Queue can be LIFO or FIFO
* In a deque you can insert or remove elements from both ends

Question 7

Give a short description of the interface: Iteratir, ListIterator

Answer 7

• You can transverse over the container in the foward direction if a class implements the Iterator interface
• You can traverse in both foward and reverse direction if a class implements the ListIterator interface

Question 8

Which are the import concrete classes in the Collection Framework?

Answer 8

• ArrayList
• LinkedList
• HashSet
• TreeSet
• HashMap
• TreeMap
• PriorityQueue

Question 9

Give a brief description of the concrete class ArrayList

Answer 9

• Implemented as a resizable array
• Fast to serach
• Slow to delete/insert
• allow dups

Question 10

Give a brief description of the concrete class LinkedList

Answer 10

• Doubly linked list data strut
• Fast to insert or delete elements
• slow for searching elements
• can be used when you need stack (LIFO) or Queue(FIFO)
• allow dups

Question 11

Give a brief description of the concrete class HashSet

Answer 11

• hash table data structure
• does not allow dups
• fast for earching and retrieving elements
• does NOT maintain any order

Question 12

Give a brief description of the concrete class TreeSet

Answer 12

• red-black tree data structure
• does not allow dup
• store elements in a sorted order

Question 13

Give a brief description of the concrete class HashMap

Answer 13

• hash-table data structure
• key values pair
• uses hashing for finding a place to search or store a pair
• searching or inserting is very fast
• not store elements in order

Question 14

Give a brief description of the concrete class TreeMap

Answer 14

• red-black tree data structure

- store elements in a sorted order

Question 15

Give a brief description of the concrete class PriorityQueue

Answer 15

• heap data structure
• retrieving based on priority
• irrespective of the order in which you insert

Question 16

Given a list:

ArrayList{String} languageList = new ArrayList{}()

how to iterate over the list using iterator?

Answer 16

for(Iterator{String} languageIter = languageList.iterator(); languageIter.hasNext();) {
String language = languageIter.next();
System.out.println(language);
}

Question 17

What is the difference between ArrayList and ArrayDeque?

Answer 17

The difference is that you can add an element anywhere in a array list using an index; however, you can add an element only either at the front or end of the array deque.

That makes insertion in array deque more efficient than array list; however, navigation in an array deque becomes more expensive than in array list

Question 18

What is the method the Comparable interface has?

Answer 18

int compareTo(Element that)

Question 19

Regards to comparings its, what should the int value be?

Answer 19

1 if current object more than passed object
0 if equal
-1 current object less than passed object

Question 20

Of all the java.util package classes, which ones are thread-safe?

Answer 20

Only Vector and Hashtable

 java.util.Collections class contains a synchronizedCollection method that creates thread-safe instances based on collections which are not. For example: 
Set s = Collections.synchronizedSet(new HashSet());