Deck 15: The Java Collections Framework

Question 1

A collection that remembers the order of items, and allows items to be added and removed only at one end is called a ____.

A) list
B) stack
C) set
D) queue

Answer 1

B

Question 2

A stack is a collection that ____.

A) remembers the order of elements, and allows elements to be added and removed only at one end.
B) does not remember the order of elements but allows elements to be added in any position.
C) remembers the order of elements and allows elements to be inserted in any position.
D) remembers the order of elements and allows elements to be inserted only at one end and removed only at the other end.

Answer 2

A

Question 3

Rather than storing values in an array, a linked list uses a sequence of ____.

A) indexes
B) nodes
C) elements
D) accessors

Answer 3

B

Question 4

Which nodes need to be updated when we insert a new node to become the fourth node from the beginning of a doubly-linked list?

A) The current third node.
B) The current third and fourth nodes.
C) The current first node.
D) The current fourth and fifth nodes.

Question 5

We might choose to use a linked list over an array list when we will not require frequent ____.
I random access
II inserting new elements
III removing of elements

A) I
B) II
C) III
D) II and III

Question 6

A linear search only requires ____ access.

A) sequential
B) random
C) sorted
D) arbitrary

Question 7

Which of the following statements about linked lists is correct?

A) Once you have located the correct position, adding elements in the middle of a linked list is inefficient.
B) Visiting the elements of a linked list in random order is efficient.
C) When a node is removed, all nodes after the removed node must be moved down.
D) Linked lists should be used when you know the correct position and need to insert and remove elements efficiently.

Question 8

A collection without an intrinsic order is called a ____.

A) list
B) stack
C) set
D) queue

Question 9

Consider the following code snippet: LinkedList words = new LinkedList();
Words.addLast("abc");
Words.addLast("def");
Words.addLast("ghi");
System.out.print(words.removeLast());
System.out.print(words.removeFirst());
System.out.print(words.removeLast());
What will this code print when it is executed?

A) abcdefghi
B) ghiabcdef
C) abcghidef
D) defghiabc

Question 10

Which data structure would best be used for keeping track of a growing set of groceries to be purchased at the food market?

A) queue
B) stack
C) list
D) array

Question 11

What is included in a linked list node?
I a reference to its neighboring nodes
II an array reference
III a data element

A) I
B) II
C) II and III
D) I and III

Question 12

What type of access does a LinkedList provide for its elements?

A) sequential
B) semi-random
C) random
D) sorted

Question 13

A collection that allows speedy insertion and removal of already-located elements in the middle of it is called a ____.

A) linked list
B) stack
C) set
D) queue

Question 14

Which of the following algorithms would be efficiently executed using a LinkedList?

A) Tracking paths in a maze.
B) Binary search.
C) Remove first n/ 2 elements from a list of n elements.
D) Read n / 2 elements in random order from a list of n elements.

Question 15

The ArrayList class implements the ____.

A) Queue interface.
B) Set interface.
C) List interface.
D) Stack interface.

Question 16

A list is a collection that ____.

A) should be used when you need to remember the order of elements in the collection.
B) allows items to be added at one end and removed at the other end.
C) does not allow elements to be inserted in any position.
D) manages associations between keys and values.

Question 17

A collection that allows items to be added only at one end and removed only at the other end is called a ____.

A) list
B) stack
C) set
D) queue

Question 18

Select an appropriate expression to complete the following code segment, which is designed to print a message if the string stored in name is part of the players collection. Collection players = new ArrayList();
// code to add elements to the collection here
If ______________________________________
System.out.print(name + " is one of the players in the collection.");

A) (players.indexOf(name))
B) (players.contains(name))
C) (players.search(name))
D) (players.equals(name))

Question 19

A queue is a collection that ____.

A) remembers the order of elements, and allows elements to be added and removed only at one end.
B) does not remember the order of elements but allows elements to be added in any position.
C) remembers the order of elements and allows elements to be inserted in any position.
D) remembers the order of elements and allows elements to be inserted only at one end and removed only at the other end.

Question 20

A binary search requires ____ access.

A) sequential
B) random
C) sorted
D) arbitrary

Question 21

Consider the following code snippet: LinkedList words = new LinkedList();
Words.addFirst("abc");
Words.addLast("def");
Words.addFirst("ghi");
System.out.print(words.removeLast());
System.out.print(words.removeFirst());
System.out.print(words.removeLast());
What will this code print when it is executed?

A) abcdefghi
B) ghiabcdef
C) abcghidef
D) defghiabc

Question 22

When using a list iterator, on which condition will the IllegalStateException be thrown?

A) Calling remove after calling next.
B) Calling add after calling previous.
C) Calling remove after calling add.
D) Calling previous after calling previous.

Question 23

You use a(n) ____ to access elements inside a linked list.

A) accessor
B) index
C) list iterator
D) queue

Question 24

What can a generic class be parameterized for?

A) properties
B) iterators
C) type
D) methods

Question 25

Assume you have created a linked list name myList that currently holds some number of String objects. Which of the following statements correctly removes an element from the end of myList?

A) myList.remove();
B) myList.removeLast();
C) myList.getLast();
D) myList.pop();

Question 26

The term ____ is used in computer science to describe an access pattern in which the elements are accessed in arbitrary order.

A) sequential access
B) random access
C) sorted access
D) arbitrary access

Question 27

Select an appropriate expression to complete the following method, which is designed to visit the elements in theList and replace each occurrence of the string "hello" with the string "goodbye". public static void helloGoodbye(LinkedList theList)
{
ListIterator iterator = theList.listIterator();
While (iterator.hasNext())
{
If (iterator.next().equals("hello"))
{
_____________________________
}
}
}

A) iterator.replace("hello", "goodbye");
B) iterator.next() = "goodbye";
C) iterator.previous("goodbye");
D) iterator.set("goodbye");

Question 28

Which of the following statements about the LinkedList class is correct?

A) When you use the add method, the new element is inserted before the iterator, and the iterator position is advanced by one position.
B) When you use the add method, the new element is inserted after the iterator, and the iterator position is advanced by one position.
C) When you use the add method, the new element is inserted before the iterator, and the iterator position is not moved
D) When you use the add method, the new element is inserted after the iterator, and the iterator position is not moved.

Question 29

Select an appropriate expression to complete the following code segment, which is designed to print a message if the string stored in name is the first element of the players linked list. LinkedList players = new LinkedList();
// code to add elements to the linked list
If ______________________________________
System.out.print(name + " is the first player on the list.");

A) (players.indexOf(name) == 1)
B) (players.contains(name))
C) (players.getFirst().equals(name))
D) (players[0].equals(name))

Question 30

What is the meaning of the type parameter E, in the LinkedList code fragment?

A) The elements of the linked list are of class E.
B) The elements of the linked list are of any subclass of class E.
C) The elements of the linked list are any type supplied to the constructor.
D) The elements of the linked list are of class Object.

Question 31

Which method is NOT part of the ListIterator generic class?

A) hasNext
B) hasMore
C) hasPrevious
D) add

Question 32

A linked list ____ encapsulates a position anywhere inside the linked list.

A) accessor
B) index
C) operation
D) iterator

Question 33

Which Java package contains the LinkedList class?

A) java.lang
B) java.util
C) java.collections
D) java.io

Question 34

When using a list iterator, on which condition will the NoSuchElementException be thrown?

A) Calling next when you are past the end of the list.
B) Calling next when the iterator points to the last element.
C) Calling remove after calling add.
D) Calling remove after calling previous.

Question 35

A(n) ____ is a data structure used for collecting a sequence of objects that allows efficient addition and removal of already-located elements in the middle of the sequence.

A) stack
B) queue
C) linked list
D) priority queue

Question 36

Consider the code snippet shown below. Assume that employeeNames is an instance of type LinkedList. for (String name : employeeNames)
{
// Do something with name here
}
Which element(s) of employeeNames does this loop process?

A) no elements
B) all elements
C) elements meeting a condition
D) the most recently added elements

Question 37

Which method is NOT part of the ListIterator interface?

A) delete
B) add
C) next
D) previous

Question 38

Assume you have created a linked list named myList that currently holds some number of String objects. Which of the following statements correctly adds a new element to the beginning of myList?

A) myList.addFirst("Harry");
B) myList.add("Harry");
C) myList.insert("Harry");
D) myList.put("Harry");

Question 39

When using a list iterator, on which condition will the IllegalStateException be thrown?

A) Calling remove after calling next.
B) Calling next after calling previous.
C) Calling remove after calling remove.
D) Calling remove after calling previous.

Question 40

Select an appropriate expression to complete the method below. The method should return the number of times that the string stored in name appears in theList. public static int count(LinkedList theList, String name)
{
Int number = 0;
Iterator iter = theList.iterator();
While (______________________)
{
If (iter.next().equals(name))
{
Number++;
}
}
Return number;
}

A) iter.hasNext()
B) iter.next() != null
C) theList.hasNext()
D) theList.next() != null

Question 41

Which of the following statements about manipulating objects in a set is correct?

A) If you try to add an element that already exists, an exception will occur.
B) If you try to remove an element that does not exist, an exception will occur.
C) You can add an element at the position indicated by an iterator.
D) A set iterator visits elements in the order in which the set implementation keeps them.

Question 42

A linked list allows ____ access, but you need to ask the list for an iterator.

A) sequential
B) random
C) sorted
D) arbitrary

Question 43

Assume that you have declared a set named mySet to hold String elements. Which of the following statements will correctly remove an element from mySet?

A) mySet.get("apple");
B) mySet.remove("apple");
C) mySet.pop("apple");
D) mySet.delete("apple");

Question 44

Which of the following statements about sets is correct?

A) Inserting and removing elements that have already been located is faster with a list than with a set.
B) A set allows duplicate values.
C) You can add an element to a specific position within a set.
D) A set is a collection of unique elements organized for efficiency.

Question 45

In a linked list data structure, when does the reference to the first node need to be updated?
I inserting into an empty list
II deleting from a list with one node
III deleting an inner node

A) I
B) II
C) I and II
D) III

Question 46

Which of the following statements about manipulating objects in a map is NOT correct?

A) Use the add method to add a new element to the map.
B) Use the get method to retrieve a value from the map.
C) Use the keyset method to get the set of keys for the map.
D) Use the remove method to remove a value from the map.

Question 47

The nodes of a(n) ____ linked list class store two links: one to the next element and one to the previous one.

A) array
B) singly
C) doubly
D) randomly

Question 48

Consider the following code snippet: LinkedList myLList = new LinkedList();
MyLList.add("Mary");
MyLList.add("John");
MyLList.add("Sue");
ListIterator iterator = myLList.listIterator();
Iterator.next();
Iterator.next();
Iterator.add("Robert");
Iterator.previous();
Iterator.previous();
Iterator.remove();
System.out.println(myLList);
What will be printed when this code is executed?

A) [Mary, John, Robert, Sue]
B) [Mary, John, Sue]
C) [Mary, Robert, Sue]
D) [John, Robert, Sue]

Question 49

Assume you are using a doubly-linked list data structure with many nodes. What is the minimum number of node references that are required to be modified to remove a node from the middle of the list? Consider the neighboring nodes.

A) 1
B) 2
C) 3
D) 4

Question 50

To create a TreeSet for a class of objects, the object class must ____.

A) create an iterator.
B) implement the Comparable interface.
C) implement the Set interface.
D) create a Comparator object.

Question 51

Which of the following statements about the TreeSet class is NOT correct?

A) Elements are stored in sorted order.
B) Elements are arranged in linear fashion.
C) Elements are stored in nodes.
D) To use a TreeSet, it must be possible to compare the elements.

Question 52

Complete the following code snippet, which is intended to determine if a specific value in a variable named targetWord appears in a set of String values named mySet: for (String aWord : mySet)
{
_______________________
{
System.out.println ("The word " + targetWord + " was found.");
}
)

A) if (mySet.equalsIgnoreCase(targetWord))
B) if (mySet == targetWord)
C) if (mySet.contains(targetWord))
D) if (mySet.get(targetWord))

Question 53

Assume that you have declared a set named mySet to hold String elements. Which of the following statements will correctly insert an element into mySet?

A) mySet.insert("apple");
B) mySet.put(apple");
C) mySet.push("apple");
D) mySet.add("apple");

Question 54

Select an appropriate declaration to complete the following code segment, which is designed to read strings from standard input and display them in increasing alphabetical order, excluding any duplicates. _________________________________________
Scanner input = new Scanner(System.in);
While (input.hasNext())
{
Words.add(input.next());
}
System.out.print(words);

A) LinkedList words = new LinkedList();
B) Set words = new Set();
C) Set words = new HashSet();
D) Set words = new TreeSet();

Question 55

Which of the following statements about manipulating objects in a set is correct?

A) If you try to add an element that already exists, an exception will occur.
B) A set iterator visits elements in the order in which they were added to the set.
C) You can add an element at the position indicated by an iterator.
D) You can remove an element at the position indicated by an iterator.

Question 56

Complete the following code, which is intended to print out all key/value pairs in a map named myMap that contains String data for student IDs and names: Map myMap = new HashMap();
) . .
Set mapKeySet = myMap.keySet();
For (String aKey : mapKeySet)
{
___________________________;
System.out.println("ID: " + aKey + "->" + name);
}

A) String name = myMap.get(aKey);
B) String name = myMap.next(aKey);
C) String name = MapKeySet.get(aKey);
D) String name = MapKeySet.next(aKey);

Question 57

Select an appropriate expression to complete the following method, which is designed to return the number of elements in the parameter array numbers. If a value appears more than once, it should be counted exactly once. public static int countElementsOnce(int[] numbers)
{
Set values = new HashSet();
For (int num: numbers)
{
Values.add(num);
}
______________________
}

A) return numbers.length;
B) return values.length();
C) return values.size();
D) return numbers.length - values.size();

Question 58

Which of the following statements about hash tables is NOT correct?

A) Elements are grouped into smaller collections that share the same characteristic.
B) You can form hash tables holding objects of type String.
C) You can add an element to a specific position within a hash table.
D) The value used to locate an element in a hash table is called a hash code.

Question 59

Which of the following statements about data structures is correct?

A) Inserting and removing elements that have already been located is faster with a list than with a set.
B) Accessing elements in a linked list in a random fashion is efficient.
C) Adding and removing already-located elements in the middle of a linked list is efficient.
D) A set is an ordered collection of unique elements.

Question 60

Complete the following code, which is intended to print out all key/value pairs in a map named myMap that contains String data for student IDs and names: Map myMap = new HashMap();
) . .
_______________________________
For (String aKey : mapKeySet)
{
String name = myMap.get(aKey);
System.out.println("ID: " + aKey + "->" + name);
}

A) Map mapKeySet = myMap.keySet();
B) Set mapKeySet = myMap.keySet();
C) Set mapKeySet = myMap.getKeySet();
D) Set mapKeySet = myMap.keySet();

Question 61

You need to access values by an integer position. Which collection type should you use?

A) Map
B) Hashtable
C) ArrayList
D) Queue

Question 62

What operation is least efficient in a LinkedList?

A) Adding an element in a position that has already been located.
B) Linear traversal step.
C) Removing an element when the element's position has already been located.
D) Random access of an element.

Question 63

You need to write a program to simulate the effect of adding an additional cashier in a supermarket to reduce the length of time customers must wait to check out. Which data structure would be most appropriate to simulate the waiting customers?

A) map
B) stack
C) queue
D) linked list

Question 64

You need to access values in objects by a key that is not part of the object. Which collection type should you use?

A) Map
B) Hashtable
C) ArrayList
D) Queue

Question 65

Which data structure would best be used for storing a set of numbers and sorting them in ascending order?

A) queue
B) stack
C) list
D) array

Question 66

Assume that you have declared a map named myMap to hold String elements with Integer keys. Which of the following statements will correctly insert an element into myMap?

A) myMap.insert(3, "apple");
B) myMap.put(3, "apple");
C) myMap.push(3, "apple");
D) myMap.add(3, "apple");

Question 67

Consider the following code snippet: Map scores;
You expect to retrieve elements randomly by key, and want fastest retrieval times. Which of the following statements will create a structure to support this?

A) scores = new HashMap;
B) scores = new TreeMap;
C) scores = new Map;
D) scores = new TreeSet;

Question 68

You need to access values in the order in which they were added (first in, first out), and not randomly. Which collection type should you use?

A) Map
B) Hashtable
C) Stack
D) Queue

Question 69

You have decided to store objects of a class in a TreeSet structure. Which of the following statements is correct?

A) If the object class implements the Comparable interface, and the sort order in the compare method is acceptable, you do not have to do anything else.
B) If the object class implements the Comparable interface, and the sort order in the compareTo method is acceptable, you do not have to do anything else.
C) If the object class implements the Comparable interface, and the sort order in the compare method is acceptable, you must create a comparator object.
D) If the object class implements the Comparable interface, and the sort order in the compareTo method is acceptable, you must create a comparator object.

Question 70

Assume that you have declared a map named myMap to hold String elements with Integer keys. Which of the following statements will correctly retrieve the value of an element from myMap by using its key?

A) myMap.get("apple");
B) myMap.peek("apple");
C) myMap.get(3);
D) myMap.peek(3);

Question 71

You want to enumerate all of the keys in a map named myMap whose keys are type String. Which of the following statements will allow you to do this?

A) Set keySet = myMap.keySet();
For (String key : keySet) {. . . }
B) Set keySet = myMap.getKeys();
For (String key : keySet) {. . . }
C) Set keySet = myMap.keys();
For (String key : keySet) {. . . }
D) Set keySet = myMap.getKeySet();
For (String key : keySet) {. . . }

Question 72

You need to write a program to build and maintain an address book. Since the program must support the possibility of having duplicate names, which data structure would be most appropriate to model this situation?

A) map
B) stack
C) queue
D) linked list

Question 73

You need to access values in the opposite order in which they were added (last in, first out), and not randomly. Which collection type should you use?

A) Map
B) Hashtable
C) Stack
D) Queue

Question 74

Which of the following statements about manipulating objects in a map is NOT correct?

A) If you attempt to retrieve a value with a key that is not associated with any value, you will receive a null result.
B) You cannot change the value of an existing association in the map; you must delete it and re-add it with the new values.
C) Use the get method to retrieve a value associated with a key in the map.
D) Use the put method to add an element to the map.

Question 75

Your program uses a Map structure to store a number of user ids and corresponding email addresses. Although each user must have a unique id, two or more users can share the same email address. Select an appropriate expression to complete the method below, which adds a new id and email address to the map only if the id is not already in use. If the id is already in use, an error message is printed. public static void addUserID(Map users, String id, String email)
{
String currentEmail = users.get(id);
If (___________________)
{
Users.put(id, email);
}
Else
{
System.out.println(id + " is already in use.");
}
}

A) currentEmail.equals(email)
B) !currentEmail.equals(email)
C) currentEmail == null
D) currentEmail != null

Question 76

You need to access values using a key, and the keys must be sorted. Which collection type should you use?

A) TreeMap
B) ArrayList
C) HashMap
D) Queue

Question 77

You need to access values by their position. Which collection type should you use?

A) TreeSet
B) ArrayList
C) Stack
D) Queue

Question 78

Consider the following code snippet:
Map scores;
If you need to visit the keys in sorted order, which of the following statements will create a structure to support this?
a) scores = new HashMap;
b) scores = new TreeMap;
c) scores = new Map;
d) scores = new HashTable;

Question 79

Assume that you have declared a map named myMap to hold String elements with Integer keys. Which of the following statements will correctly remove an element from myMap?

A) myMap.get(3);
B) myMap.remove(3);
C) myMap.pop(3);
D) myMap.delete(3);

Question 80

Which of the following algorithms would be efficiently executed on an ArrayList?

A) add 1 element to the middle of a list with n elements
B) add n / 2 elements to a list with n / 2 elements
C) remove first n / 2 elements from a list of n elements
D) read n / 2 elements in random order from a list of n elements