Collections

Question 1

General collection interfaces

Answer 1

(Collection, Set, Map, List, Queue, SortedSet, SortedMap)

Question 2

Interfaces extending Collection. Is Map part of Collection interface?

Answer 2

List, Set, Queue
Map is not collection

Question 3

TreeSet vs TreeMap

Answer 3

TreeMap allows duplicate values, TreeSet - no
TreeMap is sorted based on keys while TreeSet is sorted based on objects

Question 4

HashMap vs Hashtable

Answer 4

Hashtable is synchronized, whereas HashMap is not.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.

Question 5

Requirements for implementation of hashCode to achieve best performance

Answer 5

uniform distribution
alwasy return the same value for same object
same value for equal objects

Question 6

Differences between Hashtable and ConcurrentHashMap

Answer 6

ConcurrentHashMap uses multiple locks
Hashtable uses single lock

ConcurrentHashMap locking is applied only for updates. In case of retrievals, it allows full concurrency

Question 7

EnumSet, EnumMap

Answer 7

EnumSet, EnumMap - their elements/keys come from a single enum type

Question 8

WeakHaskMap

Answer 8

the keys of the map are stored in a weakreference
key-value pairs can dynamically be dropped from the map when the only reference to the key is from the weak reference

Question 9

IdentityHashMap

Answer 9

using reference-equality in place of object-equality when comparing keys (and values)

Question 10

Implementation details of about ConcurrentHashMap. Synchronization.

Answer 10

lock on buckets instead of whole map

Question 11

Iterator and modification of a List. ConcurentModificationException.

Answer 11

occurs when something we are iterating is changed