Java SCJP Collection 1

Question 1

Which collection class(es) allows you to grow or shrink its size and provides indexed access to
its elements, but whose methods are not synchronized? (Choose all that apply.)

Accepted Answer

java.util.ArrayList

Answer

java.util.HashSet

Answer

java.util.List

Answer

java.util.Vector

Answer

java.util.PriorityQueue

Answer

java.util.LinkedHashSet

Question 2

Which one of the following is true about natual order and insertion order ?

Accepted Answer

insertion order means that the order in which the items are inserted into the collection

Accepted Answer

Natural order is different from insertion order is that the order incase of natural is determined by observing the data in the object in context

Accepted Answer

Natural order is not same as insertion order

Answer

insertion order is determined by seeing if the element is inserted into the collection by using the insert() or add().

Question 3

Wchich implementation of Set would you choose if the you want the iterator of set would geive you objects in the order it were inserted ?

Accepted Answer

LinkedHashSet

Answer

TreeSet

Answer

HashSet

Question 4

What is the data structure that a Set uses to store its elements  ?

Accepted Answer

Map

Answer

array

Answer

object

Answer

ArrayList

Question 5

Set allows at most one null element ?

Accepted Answer

True

Answer

False

Question 6

If you were to use a List implementation,but not sure which one to, bacause the requirement is not yet clear. In this case which List implementation will you use  ?

Accepted Answer

ArrayList

Answer

Vector

Answer

LinkedList

Question 7

If you were to store objects into an implementation of List which happens only once in the entire lifecycle of the product,but reading these objects inside the List implementation is quite high,then  which one would  you use ?

Accepted Answer

ArrayList

Answer

Vector

Answer

LinkedList

Question 8

Which of the following implementation will you use if you were to insert elements at any position in the collection ?

Accepted Answer

LinkedList

Answer

ArrayList

Answer

Vector

Question 9

The EMPTY_LIST field and teh emptyList() method does return an empty immutable List .(The same also applies to
EMPTY_SET,EMPTY_MAP and corresponding methods emptySet,emptyMap). Which of the following is/are true ?

Accepted Answer

The field gives you a non type-safe empty immutable object where are the method return type-safe empty immutable object of collection

Accepted Answer

The emptyXxx() methods actually returns the EMPTY_XXX fields.

Answer

There is no difference between the field and emptyList() ways to fetch an empty immutable list

Answer

The method to get the empty immutable collections are not static, so we need to create an object of Collections class in-order to call these methods,so fields like EMPTY_XXX are better choice if one doesn't want to create object of Collections.

Question 10

Which of the following is true about creating an empty List, but immutable ?

Accepted Answer

List immutableEmptyList=Collections.EMPTY_LIST

Accepted Answer

List immutableEmptyList=Collections.unmodifiableList(new ArrayList());

Answer

final List immutableEmptyList=new ArrayList();

Answer

List immutableEmptyList=Collections.unmodifiableList(new List());

Question 11

How do you get immutable object of a collection ? For example if you were to write an API which return a List or a Set or a Map when a method is called, but you also want that you don't want the client of your API to add or delete any object in the returned collection ?

Accepted Answer

Use the Collections.unmodifiableXxxx() method with the collection as an argument,which returns an immutable object of specific type.

Answer

Use Collections.immutableCollection() method.

Question 12

Enumeration is an interface helps to iterate collection,but it can't remove any element the collection it is iterating

Accepted Answer

True

Answer

False

Question 13

which of the following are false about Collections and Collection ?

Accepted Answer

Collections is a special type of collection which holds Set of collections

Answer

Collections is a utility class

Answer

Collection is an interface to Set and List

Answer

Both Collections and Collection entity belongs to java.util package.

Question 14

Which of the following Collection are synchronized by nature ?

Accepted Answer

Vector

Accepted Answer

Hashtable

Answer

SortedSet

Answer

HashMap

Question 15

Which of the following are true about  ListIterator and Iterator ?

Accepted Answer

Iterator can traverse in forward direction only

Accepted Answer

ListIterator can traverse lists in both direction

Accepted Answer

ListIterator extends the Iterator interface

Accepted Answer

Iterator can remove the elements

Answer

Iterator can do operations like modifying the items it holds.

Java SCJP Collection 1

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