ITSW 3173 D287 Java Frameworks

Correct Answer

A. HashSet, LinkedHashSet, TreeSet

Explanation

In Java, the Set interface is primarily implemented through HashSet, LinkedHashSet, and TreeSet. Each serves a different purpose: HashSet offers constant-time performance and does not maintain order, LinkedHashSet maintains insertion order, and TreeSet keeps elements sorted. These are the most commonly used and recognized implementations in the Java Collections Framework.

Why other options are wrong

B. ArrayList, HashMap, TreeSet

This is incorrect because ArrayList and HashMap are not implementations of the Set interface. ArrayList implements List, while HashMap implements the Map interface. Only TreeSet in this option is a valid Set implementation.

C. LinkedList, HashSet, PriorityQueue

This option is wrong because LinkedList and PriorityQueue are not part of the Set family. LinkedList is a List implementation, and PriorityQueue is a Queue. Only HashSet qualifies as a Set.

D. HashMap, ArrayList, LinkedHashSet

This is incorrect since HashMap and ArrayList do not implement the Set interface. HashMap belongs to the Map family, and ArrayList to List. Only LinkedHashSet correctly belongs to the Set interface.

Correct Answer

C. If you do not, it could be possible to insert duplicates

Explanation

In a HashSet, the equals and hashCode methods are used to determine whether two objects are the same. If the equals method is not overridden, objects might be considered equal even if they are not. Similarly, if hashCode is not overridden, two objects that are logically equal might end up with different hash codes, leading to potential duplicates in the set. Overriding both methods ensures that objects are properly compared for equality and managed correctly in the HashSet.

Why other options are wrong

A. If you do not, the code will have a compilation error

This is incorrect because not overriding equals and hashCode does not cause a compilation error. The program will still compile, but the behavior of HashSet may not work as expected.

B. If you do not, all objects of type X will be considered equal

This is incorrect because, by default, the equals method from the Object class compares object references. Without overriding equals, only objects with the same memory address (reference) will be considered equal, not all objects of type X.

D. You do not need to override both methods in X in order to successfully store objects of type X in a HashSet

This is incorrect because not overriding both methods can lead to issues with object comparison and insertion in a HashSet. It is important to override both equals and hashCode to ensure proper behavior in sets and maps.

Correct Answer

C. A First-In/First-Out data structure

Explanation

A Queue in the Java Collections Framework follows the First-In/First-Out (FIFO) principle. This means that the element that is added first will be the first one to be removed, much like a line at a checkout counter. It does not support random access to its elements and is designed to process elements in a specific order.

Why other options are wrong

A. A structure that allows random access to elements

This is incorrect. A Queue does not allow random access to elements. You can only remove or inspect elements from the front (or sometimes the rear) of the queue, depending on the specific type of queue (like LinkedList or PriorityQueue).

B. A data structure that follows Last-In/First-Out principle

This is incorrect. The Last-In/First-Out (LIFO) principle applies to a Stack, not a Queue. In a Queue, the first element added is the first one to be removed (FIFO).

D. A collection that stores unique elements only

This is incorrect. A Queue does not guarantee uniqueness of its elements. If uniqueness is required, a Set implementation like HashSet would be used.

Correct Answer

A. ArrayList & LinkedList

Explanation

The List interface in the Java Collections Framework provides an ordered collection of elements that can be accessed by index. The two primary implementations of the List interface are ArrayList and LinkedList. ArrayList uses a dynamic array to store elements, while LinkedList uses a doubly linked list.

Why other options are wrong

B. String & ArrayList

This is incorrect because String is a class in Java, not an implementation of the List interface. ArrayList is indeed an implementation of List, but String is unrelated to the List interface in this context.

C. StringList & LinkedList

This is incorrect because StringList is not a part of the Java Collections Framework. The valid implementations of the List interface are ArrayList and LinkedList, not StringList.

D. Map & Stack

This is incorrect because Map is a different interface, not a subclass of List. The Stack class is a subclass of Vector, which implements the List interface, but Map and Stack are not part of the same set of implementations for List.

Correct Answer

B. LinkedHashSet

Explanation

LinkedHashSet is a type of Set that maintains the order of elements in the sequence in which they were inserted. It ensures that there are no duplicates and that the order of insertion is preserved, which is not guaranteed by a standard HashSet.

Why other options are wrong

A. HashSet

This is incorrect because HashSet does not guarantee any specific order of the elements. It stores elements without duplicates, but the order of insertion is not preserved.

C. TreeSet

This is incorrect because TreeSet stores elements in a sorted order according to their natural ordering or a specified comparator. It does not maintain insertion order.

D. ArrayList

This is incorrect because ArrayList is a type of List, which allows duplicates and does not enforce any rules about unique elements. It also does not automatically ensure that duplicates are removed.

E. LinkedList

This is incorrect because LinkedList is a type of List that maintains the order of elements, but it allows duplicates. It is not specifically used for enforcing uniqueness like a Set.

Correct Answer

B. By implementing a doubly linked list

Explanation

A LinkedHashMap maintains the insertion order (or access order, if specified) of its entries by using a doubly linked list that connects all of the entries. This is in contrast to a regular HashMap, which does not guarantee any specific order. The doubly linked list preserves the order in which keys were inserted or accessed.

Why other options are wrong

A. By using a Tree structure for storage

This is incorrect because a tree structure is used in TreeMap, not LinkedHashMap. A TreeMap sorts entries by their keys, while a LinkedHashMap maintains order based on insertion or access.

C. By sorting entries based on keys

This describes the behavior of a TreeMap, which sorts keys based on their natural order or a specified comparator. LinkedHashMap does not sort by keys but retains the order in which keys were inserted or accessed.

D. By using a priority queue

This is incorrect because PriorityQueue is a separate collection type that orders elements based on priority, not key-value pair access or insertion. LinkedHashMap does not utilize a priority queue mechanism to maintain order.

Correct Answer

A. To define a set of methods for manipulating data structures

Explanation

The Collection interface is the root interface in the Java Collections Framework and defines a set of general methods for manipulating collections of objects. This includes operations like adding, removing, and checking for the presence of elements. It provides the fundamental behaviors for all types of collections such as lists, sets, and queues. Other specific interfaces like Set, List, and Queue extend Collection and define additional methods suited for their particular behavior, but Collection itself lays out the core functionality.

Why other options are wrong

B. To provide a way to store key-value pairs

This is incorrect. The Collection interface does not provide a way to store key-value pairs. That functionality is provided by the Map interface, which is separate from Collection.

C. To manage a collection of unique elements

This is incorrect. The Collection interface itself does not enforce uniqueness. It is the Set interface, which is a subclass of Collection, that ensures no duplicate elements. The Collection interface can be implemented by any collection, including lists (which can allow duplicates).

D. To facilitate the traversal of tree structures

This is incorrect. While the Collection interface provides methods for iterating through elements, it does not specifically facilitate the traversal of tree structures. Tree structures like binary trees are typically managed by specific classes such as TreeSet or TreeMap, which implement other interfaces like NavigableSet or NavigableMap.

Correct Answer

B. Set, List, Queue

Explanation

The Java Collections Framework provides several core interfaces. The primary ones that extend the Collection interface are List, Set, and Queue. These interfaces define common behaviors for groups of objects and are widely used in Java programming to manage collections of elements. Map does not extend the Collection interface and operates differently, associating keys with values.

Why other options are wrong

A. Map, List, Set

This is incorrect because Map is not part of the Collection interface hierarchy. Although it is part of the Collections Framework, it uses a different structure that focuses on key-value pairs. Therefore, it cannot be grouped with the other types that extend Collection.

C. List, Stack, Array

This is incorrect because Stack is a legacy class that extends Vector and is not considered a primary collection type under the Collection interface. Additionally, Array is not part of the Collections Framework but rather a core language structure in Java, and it doesn’t implement the Collection interface.

D. Queue, Map, Stack

This is incorrect because, again, Map is not part of the Collection interface. Stack, as noted earlier, is a legacy class and not one of the main interfaces under Collection. Only Queue from this group extends the Collection interface directly.

Correct Answer

C. A collection that maintains the order of elements based on their insertion

Explanation

In the Java Collections Framework, a List is an ordered collection that maintains the order of elements based on their insertion. This means that elements in a List are stored in the order they are added, and their positions can be indexed (e.g., using the get() method). The List interface allows for duplicate elements, unlike sets, and provides a way to store elements in a predictable sequence.

Why other options are wrong

A. A collection that allows for unique elements only

This is incorrect because a List allows duplicate elements. Unlike a Set, which only allows unique elements, a List can store multiple occurrences of the same element.

B. A collection that stores elements in a random order

This is incorrect because a List maintains the order of elements based on their insertion, not in a random order. The order of elements is predictable, and each element has a specific index position.

D. A collection that maps keys to values

This is incorrect because a collection that maps keys to values is a Map, not a List. A Map stores key-value pairs, where each key is unique and associated with a value. A List does not have this functionality.