ITSW 3173 D287 Java Frameworks

Correct Answer

B. The elements do not implement the Comparable interface and you need a specific order for sorting.

Explanation

When working with a SortedSet, a custom comparator is necessary when the elements of the set do not implement the Comparable interface (which defines the natural ordering for objects) and you need to define a specific sorting order. The comparator allows you to dictate how the elements should be compared and ordered in the set. Without a comparator or the elements implementing Comparable, the set would not know how to sort the elements.

Why other options are wrong

A. The elements are of a type that implements the Comparable interface and you want to sort them in their natural order.

This is incorrect because when elements already implement the Comparable interface, no custom comparator is needed. The SortedSet can use the natural ordering defined by Comparable.

C. You want to sort the elements based on their hash codes.

This is incorrect because hash codes are used primarily for efficient searching and not for sorting elements. Sorting by hash codes would not generally provide meaningful order.

D. The elements are already sorted in the desired order and you want to maintain that order.

This is incorrect because if the elements are already sorted in the desired order, you don't need to provide a custom comparator. The SortedSet will maintain the order automatically as long as the elements' natural ordering or the provided comparator matches the required order.

Correct Answer

D. BinaryTree

Explanation

The BinaryTree data structure is not part of the Java Collections Framework. While trees are often used in Java, the BinaryTree itself is not a class or interface within the standard library. Java provides the TreeSet and TreeMap classes, which implement the SortedSet and SortedMap interfaces, respectively, but these are specialized forms of trees (e.g., Red-Black trees), not a generic binary tree.

Why other options are wrong

A. ArrayList

This is incorrect. ArrayList is part of the Java Collections Framework, specifically a class that implements the List interface, which is used for ordered collections that allow duplicates.

B. HashSet

This is incorrect. HashSet is part of the Java Collections Framework and implements the Set interface, which is used to store unique elements without any specific order.

C. Queue

This is incorrect. Queue is part of the Java Collections Framework and represents a collection designed for holding elements before processing, typically in FIFO order. It is implemented by classes like LinkedList and PriorityQueue.

Correct Answer

C. The HashMap class is efficient for locating a value, inserting an entry, and deleting an entry. The TreeMap class is efficient for traversing the keys in a sorted order.

Explanation

The HashMap class uses a hash table for storage, making it highly efficient for locating values, inserting new entries, and deleting entries. However, it does not maintain any specific order of the entries. On the other hand, the TreeMap class uses a Red-Black tree structure to store entries, which allows it to automatically sort the entries based on their keys. This makes TreeMap efficient for traversing keys in sorted order, but it is generally slower than HashMap for insertion, deletion, and retrieval of values because of the overhead involved in maintaining the sorted order.

Why other options are wrong

A. The TreeMap has a linked-list implementation that supports an ordering of the entries in the map. The HashMap class is efficient for traversing the keys in a sorted order.

This is incorrect because TreeMap uses a Red-Black tree for ordering, not a linked-list implementation. Additionally, HashMap does not support sorting of keys; it is unordered.

B. The HashMap has a linked-list implementation that supports an ordering of the entries in the map. The TreeMap class is efficient for traversing the keys in a sorted order.

This is incorrect because HashMap does not maintain order in any form. While it uses a linked list internally to handle hash collisions (when multiple entries hash to the same bucket), it does not preserve the order of the entries.

D. The TreeMap class is efficient for locating a value, inserting an entry, and deleting an entry. The HashMap class is efficient for traversing the keys in a sorted order.

This is incorrect because TreeMap is not necessarily more efficient than HashMap for locating a value, inserting an entry, or deleting an entry. In fact, HashMap generally offers constant-time operations for these tasks, while TreeMap has logarithmic time complexity due to the need to maintain the order of the entries.

Correct Answer

B. It ensures that elements are processed in the order they were added.

Explanation

The FIFO (First-In, First-Out) principle is fundamental to the behavior of a queue. It ensures that elements are processed in the same order they were added, meaning the first element added is the first one to be removed and processed. This order is crucial in scenarios like task scheduling, where the first task must be processed first, or in print queues, where documents are printed in the order they were sent.

Why other options are wrong

A. It allows the most recently added element to be processed first.

This is incorrect. The principle that allows the most recently added element to be processed first is known as LIFO (Last-In, First-Out), which is typical for a stack, not a queue.

C. It requires that all elements be processed simultaneously.

This is incorrect. FIFO processes elements sequentially, one at a time, based on their order of arrival. Simultaneous processing is not a characteristic of the FIFO principle.

D. It allows for random access to elements within the queue.

This is incorrect. FIFO processes elements in the order they were added and does not allow random access to elements. A queue typically follows a strict order of removal (front to back), which makes random access inappropriate for queues.

Correct Answer

B. To traverse a collection without exposing its internal structure

Explanation

The primary purpose of using an Iterator is to provide a way to traverse through the elements of a collection (such as List, Set, or Queue) without exposing its internal structure. The Iterator interface provides methods like hasNext(), next(), and remove() to iterate through the elements in a collection.

Why other options are wrong

A. To modify the underlying data structure directly

This is incorrect because an Iterator is not designed for direct modification of the collection's internal structure. It allows for element removal during iteration but does not offer direct manipulation of the collection.

C. To sort elements within a collection

This is incorrect because an Iterator does not provide any functionality for sorting elements. Sorting is typically done using methods such as Collections.sort() or by using appropriate Comparator objects.

D. To convert a collection into an array

This is incorrect because an Iterator is not used for converting a collection into an array. To convert a collection into an array, you would typically use the toArray() method, not an Iterator.

Correct Answer

E. constructor()

Explanation

The Collection interface in Java provides methods like clear(), size(), toArray(), and iterator() for managing and accessing the elements of a collection. However, a constructor is not a method of the Collection interface. Constructors are used to create instances of a class, not to define behavior in an interface.

Why other options are wrong

A. clear()

This is a method of the Collection interface. It removes all elements from the collection.

B. size()

This is a method of the Collection interface. It returns the number of elements in the collection.

C. toArray()

This is a method of the Collection interface. It returns an array containing all elements in the collection.

D. iterator()

This is a method of the Collection interface. It returns an iterator that can be used to traverse the collection.

Correct Answer

A. pop()

Explanation

The pop() method is used in a stack to remove and return the top element. In a stack, this is the primary method for removing elements, adhering to the "last in, first out" (LIFO) principle.

Why other options are wrong

B. isEmpty()

This is incorrect because isEmpty() simply checks whether the stack is empty, but it does not remove any elements.

C. peek()

This is incorrect because peek() returns the top element of the stack without removing it. It allows you to view the top element but does not perform a removal.

D. push()

This is incorrect because push() adds an element to the top of the stack. It does not remove any elements.

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

A. Sort returns a sorted collection

Explanation

The sort method in the Collections class does not return a sorted collection. Instead, it sorts the collection in place. It modifies the collection passed to it, so the method does not return a new collection. This makes it different from other methods that might return a modified copy of the collection.

Why other options are wrong

B. There are 2 overloaded sort methods. One takes one parameter, the other one two.

This is correct. The sort method has two overloaded versions: one that takes a single List parameter and sorts it in ascending order, and another that accepts a List and a Comparator as parameters, allowing you to define the sorting order (e.g., reverse order).

C. Sort returns nothing but it changes the collection that was passed as an argument

This is accurate. The sort method modifies the collection directly, and it has a void return type, meaning it does not return a sorted collection but instead sorts the original collection in place.

D. The second parameter lets you define how the collection should be sorted - for example in reverse order

This is correct. When using the overloaded sort method with two parameters, the second parameter is a Comparator that lets you specify custom sorting logic, including sorting in reverse order or any other defined order.