Question 1

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

Accepted Answer

An ArrayList allows access to its elements by integer index positions, making it suitable for accessing values by position.

Question 2

What operation is least efficient in a LinkedList?

Accepted Answer

LinkedLists do not support efficient random access because they require traversal from the head to the desired position, resulting in O(n) time complexity.

Question 3

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?

Accepted Answer

A queue is the most appropriate data structure for simulating waiting customers because it follows the First-In-First-Out (FIFO) principle, which aligns with how customers are served in a line.

Question 4

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

Accepted Answer

A Map allows you to store key-value pairs, where you can access values using keys that are not inherently part of the objects themselves.

Question 5

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

Accepted Answer

An array is a data structure that stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type instead.

Question 6

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?

Accepted Answer

In Java, the correct method to insert an element into a map is `put()`, so `myMap.put(3, "apple");` is the correct statement.

Question 7

Consider the following code snippet: Map<String, Integer> 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?

Accepted Answer

HashMap provides constant time complexity O(1) for retrieval operations by key, making it the fastest option for random access by key.

Question 8

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?

Accepted Answer

A Queue is a collection type that follows the First-In-First-Out (FIFO) principle, meaning elements are accessed in the order they were added.

Question 9

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

Accepted Answer

If the object class implements the Comparable interface and the sort order in the compareTo method is acceptable, TreeSet will use this method for ordering, and no additional comparator is needed.

Question 10

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?

Accepted Answer

The method `get()` is used to retrieve a value from a map using its key. Since `myMap` is declared to hold `Integer` keys, `myMap.get(3);` is the correct way to retrieve a value using an integer key.

Question 11

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?

Accepted Answer

keySet() is the correct method to get the set of keys from a map.

Question 12

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?

Accepted Answer

A linked list is appropriate for maintaining an address book with duplicate names, as it allows for easy insertion and traversal of entries, including duplicates.

Question 13

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?

Accepted Answer

A Stack is a collection type that follows the Last In, First Out (LIFO) principle, allowing access to elements in the reverse order of their addition.

Question 14

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

Accepted Answer

In most map implementations, you can change the value of an existing association by using the put method with the same key, which will update the value.

Question 15

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<String, String> users, String id, String email)
{
String currentEmail = users.get(id);
If (___________________)
{
Users.put(id, email);
}
Else
{
System.out.println(id + " is already in use.");
}
}

Accepted Answer

The condition `currentEmail == null` checks if the id is not already in use, allowing the new id and email to be added to the map.

Question 16

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

Accepted Answer

TreeMap is a collection that stores key-value pairs in a sorted order based on the keys.

Question 17

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

Accepted Answer

ArrayList is an ordered collection that allows duplicate elements. You can access elements by their position using the get() method.

Question 18

Consider the following code snippet:
Map<String, Integer> scores;
If you need to visit the keys in sorted order, which of the following statements will create a structure to support this?

Accepted Answer

TitleWhich statement creates a structure to support visiting elements in sorted order?

Question 19

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?

Accepted Answer

The remove() method is used to remove an element from a map.

Question 20

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

Accepted Answer

Reading elements in random order from an ArrayList is efficient because it provides O(1) time complexity for accessing elements by index.

Quiz 15: The Java Collections Framework