Generics and Collections

Question 1

When using primitive operands, how does the == operator determine equality?

Answer 1

By comparing their underlying values

Question 2

Which phrase describes the compiler replacing all generic parameters with existing types that match the required bounds or Object if the type parameter is unbounded?

Answer 2

type erasure

Question 3

Which interface provides a natural order of elements for a Map?

Answer 3

SortedMap

Question 4

What is a raw type?

Answer 4

A traditional collection that uses Object to store its elements.

Question 5

Which four methods will return the first element in a Deque?

Answer 5

pop, poll, peek, remove,

Also removeFirst, pollFirst, peekFirst, element, getFirst

Question 6

Which limitation on instantiation is a direct result of type erasure?

Answer 6

Generic parameters cannot be directly instantiated.

Question 7

Which keyword is used in conjunction with the ? character to specify a lower bound for allowable data types?

Answer 7

super

Question 8

Which type of collection cannot contain duplicate elements?

Answer 8

Set

Question 9

Which conversion between raw and parameterized types will generate an unchecked conversion warning?

Answer 9

Conversion from raw type to parameterized type

Question 10

When is the diamond operator used with a constructor to infer a type for a generic parameter?

Answer 10

The type is explicitly specified in the variable declaration.

Question 11

Which keyword is used in conjunction with the ? character to specify an upper bound for allowable data types?

Answer 11

extends

Question 12

Which interface should be implemented to sort elements in an order other than the default order in collection?

Answer 12

Comparator

Question 13

Which keyword applies to either an interface or a superclass when bounding generic parameters?

Answer 13

extends

Question 14

Which operator indicates an empty set of type parameters using type inference?

Answer 14

Diamond (<>) operator

Question 15

Which conversion does a compiler automatically provide between primitive types and corresponding object wrapper classes?

Answer 15

Autoboxing

Question 16

When using reference operands, how does the == operator determine equality?

Answer 16

By comparing their object references

Question 17

What is the primary storage and retrieval mechanism for a Map?

Answer 17

name/value pairs

Question 18

Which interface should be implemented by objects that can be sorted as elements in a collection?

Answer 18

Comparable

Question 19

Which conversion between raw and parameterized types will NOT generate an unchecked conversion warning?

Answer 19

Conversion from parameterized type to raw type

Question 20

Which character indicates a wildcard for allowable data types?

Answer 20

?

Question 21

What collection classes implement Deque and can be used to represent a LIFO stack?

Answer 21

ArrayDeque, ConcurrentLinkedDeque, LinkedBlockingDeque, LinkedList
These are preferred over Stack

Question 22

LIFO

Answer 22

Last In First Out

Question 23

ArrayDeque

Answer 23

Implements Deque and Queue

Resizable-array implementation of the Deque interface. Not thread safe.

Question 24

ConcurrentLinkedDeque

Answer 24

Implements Deque and Queue

An unbounded concurrent deque based on linked nodes. Null elements not allowed

Question 25

LinkedBlockingDeque

Answer 25

Implements BlockingQueue, Deque, Queue

An optionally-bounded blocking deque based on linked nodes.

Question 26

LinkedList

Answer 26

Implements Deque, Queue
Doubly-linked list implementation of the List and Deque interfaces. Implements all optional list operations, and permits all elements (including null).

Question 27

The add Queue method is equivalent to what Deque method?

Answer 27

addLast

Question 28

The offer Queue method is equivalent to what Deque method?

Answer 28

offerLast

Question 29

The remove Queue method is equivalent to what Deque method?

Answer 29

removeFirst

Question 30

The poll Queue method is equivalent to what Deque method?

Answer 30

pollFirst

Question 31

The element Queue method is equivalent to what Deque method?

Answer 31

getFirst

Question 32

The peek Queue method is equivalent to what Deque method?

Answer 32

peekFirst

Question 33

The push Stack method is equivalent to what Deque method?

Answer 33

addFirst

Question 34

The pop Stack method is equivalent to what Deque method?

Answer 34

removeFirst

Question 35

The peek Stack method is equivalent to what Deque method?

Answer 35

peekFirst

Question 36

Which queue and deque methods will throw an exception if an element cannot be added due to capacity restructions?

Answer 36

add, addFirst, addLast, push

Question 37

What exception is thrown by a class implementing Queue or Deque if a capacity restruction is violated on an insert?

Answer 37

IllegalStateException

Question 38

Which queue and deque methods will return a special value if an element cannot be added due to capacity restructions?

Answer 38

offer, offerFirst, offerLast

Question 39

Which blockingQueue methods will block (wait) if an element cannot be added due to capacity restructions?

Answer 39

put, putFirst, putLast

Question 40

Which blockingQueue methods will wait for a specified time if an element cannot be added due to capacity restructions?

Answer 40

offer, offerFirst, offerLast

If timeout occurs a special value is returned.

Question 41

Which retrieveal queue and deque methods will throw an exception if the queue is empty?

Answer 41

remove, removeFirst, removeLast

Question 42

Which retrieveal queue and deque methods will return a special value if the queue is empty?

Answer 42

poll, pollFirst, pollLast

Question 43

Which retrieveal queue and deque methods will wait for a value if the queue is empty?

Answer 43

take, takeFirst, takeLast

Question 44

Which inspection queue and deque methods will throw an exception if the queue is empty?

Answer 44

element, getFirst, getLast

Question 45

Which inspection queue and deque methods will return a special value if the queue is empty?

Answer 45

peek, peekFirst, peekLast

Question 46

Name two classes that implement the Map interface?

Answer 46

AbstractMap, ConcurrentHashMap, ConcurrentSkipListMap, HashMap, Hashtable, IdentityHashMap, LinkedHashMap, TreeMap, WeakHashMap

Question 47

Name two subinterfaces that extend the Map interfaces

Answer 47

ConcurrentMap, ConcurrentNavigableMap, NavigableMap

Question 48

Can the list return from Arrays.asList can be modified?

Answer 48

No, The Arrays.asList method returns a List object that is backed by a fixed-length array. You cannot modify the List object returned by this array, so calling methods such as add() or remove() will result in throwing an UnsupportedOperationException.

Question 49

What is a SkipList

Answer 49

A skip list is a data structure that allows fast search within an ordered sequence of elements. Fast search is made possible by maintaining a linked hierarchy of subsequences, each skipping over fewer elements.

Question 50

What java collection or “collection like” classes implement a skiplist structure?

Answer 50

ConcurrentSkipListSet, ConcurrentSkipListMap

Question 51

What is the difference between a LinkedListDeque and ArrayDeque?

Answer 51

LinkedList is maintaining nodes where the array is just using one big array. Array is better provided that it is sized correctly otherwise it has to double the size and copy if the number of elements exceeds the array size.

Question 52

For TreeSet, if an iterator is created and the TreeSet ojbect is modified (insert/remove) what happens with the iterator is used?

Answer 52

The iterators returned by this class’s iterator method are fail-fast: if the set is modified at any time after the iterator is created, in any way except through the iterator’s own remove method, the iterator will throw a ConcurrentModificationException.

Question 53

What is fail safe

Answer 53

TBD