Java Collection Framework Methods
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Questions and Answers

Which method removes all the elements from an invoking collection?

  • reset()
  • refresh()
  • clear() (correct)
  • delete()

    • What type of Set does Collections.emptySet() return?

  • Type-dependent Set
  • Mutable Set
  • Immutable Set (correct)
  • Null object

    • What will be the output of the following Java code snippet? Map sampleMap = new TreeMap(); sampleMap.put(1, null); sampleMap.put(5, null); sampleMap.put(3, null); sampleMap.put(2, null); sampleMap.put(4, null); System.out.println(sampleMap);

  • {1=null, 5=null, 3=null, 2=null, 4=null}
  • {1=null, 2=null, 3=null, 4=null, 5=null} (correct)
  • Exception is thrown
  • {5=null}

    • What is the initial capacity of the Vector object created with Vector obj = new Vector(4,2); before elements are added?

    <p>4 (D)</p> Signup and view all the answers

    Which of these structures is responsible for storing associations between keys and values?

    <p>Map (A)</p> Signup and view all the answers

    What will be the output of the following Java program involving a LinkedList and Collections.reverse()?

    <p>1 5 8 2 (C)</p> Signup and view all the answers

    Which method is used to search for an element in a list?

    <p>binarySearch() (A)</p> Signup and view all the answers

    How can an object be removed from an ArrayList?

    <p>remove() method and using Iterator (D)</p> Signup and view all the answers

    Which of the following options best describes the TreeMap functionality?

    <p>Maintains ordering of keys (B)</p> Signup and view all the answers

    When using a Vector with an initial capacity of 4 and increment of 2, what will be its capacity after adding 5 elements?

    <p>8 (D)</p> Signup and view all the answers

    What is the expected output when executing the Java program that declares an int array and assigns values using a for loop?

    <p>3 (D)</p> Signup and view all the answers

    What will the size of the ArrayList be after adding two elements and calling trimToSize?

    <p>2 (A)</p> Signup and view all the answers

    Which interface ensures that all elements stored are unique when implementing a data structure?

    <p>Set (C)</p> Signup and view all the answers

    What is the correct distinction between the methods length() and size() when used with an ArrayList?

    <p>length() returns the capacity of ArrayList and size() returns the actual number of elements stored in the list (D)</p> Signup and view all the answers

    How does the rear pointer of a circular queue update when inserting an element if its size is defined by MAX_SIZE?

    <p>rear=(rear+1)%MAX_SIZE (B)</p> Signup and view all the answers

    What is the expected output of the Java program that uses a LinkedList and performs actions such as reverse, shuffle, and remove?

    <p>2 1 8 (A)</p> Signup and view all the answers

    Which method would be incorrectly defined if applied to an ArrayList?

    <p>length() (B)</p> Signup and view all the answers

    In the context of Java collections, which characteristic does not apply to the List interface?

    <p>Storing unique elements (D)</p> Signup and view all the answers

    What happens to the original order of a LinkedList when the Collections.reverse() method is called?

    <p>The order is reversed (D)</p> Signup and view all the answers

    What will be the value of an array element at index 3 after the completion of a for loop filling a 5-element array with decreasing values from 5?

    <p>3 (C)</p> Signup and view all the answers

    What is the output of the following Java program when attempting to access an uninitialized array? import java.util.*; class Array { public static void main(String args[]) { int array[] = new int; for (int i = 5; i > 0; i--) array[5 - i] = i; Arrays.sort(array); for (int i = 0; i < 5; ++i) System.out.print(array[i]); } }

    <p>An ArrayIndexOutOfBoundsException (B)</p> Signup and view all the answers

    Which method is used to remove a specific element from a LinkedList object?

    <p>remove() (C)</p> Signup and view all the answers

    What is the expected output of the following program? import java.util.*; class properties { public static void main(String args[]) { Properties obj = new Properties(); obj.put("AB", new Integer(3)); obj.put("BC", new Integer(2)); obj.put("CD", new Integer(8)); System.out.print(obj.keySet()); } }

    <p>{AB, BC, CD} (D)</p> Signup and view all the answers

    Which of these options accurately describes the relationship between TreeSet and SortedSet?

    <p>SortedSet is an interface; TreeSet is a concrete class. (B)</p> Signup and view all the answers

    Given the following Java program, what will be the output? import java.util.*; class Linkedlist { public static void main(String args[]) { LinkedList obj = new LinkedList(); obj.add("A"); obj.add("B"); obj.add("C"); obj.removeFirst(); System.out.println(obj); } }

    <p>[B, C] (A)</p> Signup and view all the answers

    What will be the output of the following code with respect to Vector? import java.util.*; class vector { public static void main(String args[]) { Vector obj = new Vector(4,2); obj.addElement(new Integer(3)); obj.addElement(new Integer(2)); obj.addElement(new Integer(6)); obj.insertElementAt(new Integer(8), 2); System.out.println(obj); } }

    <p>[3, 2, 8, 6] (D)</p> Signup and view all the answers

    Which option correctly identifies a class that implements the Set interface?

    <p>HashSet (B)</p> Signup and view all the answers

    Which method will successfully add an element to the beginning of a LinkedList?

    <p>addFirst() (B)</p> Signup and view all the answers

    What does the method hasNext() accomplish when used with iterators?

    <p>Checks if there are remaining elements in the collection. (A)</p> Signup and view all the answers

    Flashcards

    Deleting all elements from a collection

    The clear() method removes all elements from a collection, leaving it empty.

    Collections.emptySet()

    Returns an immutable empty set.

    TreeMap output

    A TreeMap automatically sorts keys in ascending order.

    Vector capacity

    The capacity of a Vector object is the maximum number of elements it can hold.

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    Map object

    Stores key-value pairs.

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    Collections.reverse(list)

    Reverses the order of elements in a list.

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    Searching elements in a list

    The binarySearch() method is used for efficient searching in sorted lists.

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    Removing elements from ArrayList

    remove() method is used to remove objects from an ArrayList. Iterators are used together with remove method to remove element from ArrayList safely.

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    ArrayList size

    Returns the number of elements in an ArrayList.

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    Array sorting

    Sorts the elements of an array in ascending order using the Arrays.sort() method.

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    Iterator.next()

    Moves to the next element in a collection and returns the element.

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    LinkedList.set()

    Changes an element at a specific index in a LinkedList.

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    LinkedList.removeFirst()

    Removes and returns the first element from a LinkedList.

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    Vector.isEmpty()

    Checks if a Vector is empty.

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    Hashtable.remove()

    Removes a key-value pair from a Hashtable.

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    HashSet class

    Implements the Set interface in Java's Collection Framework.

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    SortedSet Interface

    Interface defining ordered sets. TreeSet is a concrete implementation.

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    Collection.fill()

    Replaces all elements in a List with a given object.

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    What does 'insert()' do?

    The 'insert()' method is used to insert an element at a specific position in a list. It's a common operation in data structures that allow for dynamic element insertion.

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    What is the output of this Java program?

    The output of the program is '2'. The code first initializes and fills an array with values from 1 to 5. Then, it sorts the array and uses binary search to find the index of the element '4'. Binary search effectively finds the middle element, and repeatedly searches either the left or right half until the element is found, resulting in an index of 2.

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    What is the output of this Java program?

    The output is '2'. The code initially creates an ArrayList, adds elements 'A' and 'D', then calls ensureCapacity(3), which does not change the size but reserves space for 3 elements. The subsequent trimToSize() method reduces the capacity to the current size (2), leaving the size as 2.

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    Which interface must contain unique elements?

    The Set interface must contain unique elements. It's a collection of elements with no duplicates, ensuring distinct values within the set.

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    Difference between length() and size() in ArrayList?

    In an ArrayList, length() returns the capacity (maximum elements it can hold), while size() returns the actual number of elements stored in the list.

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    How does the 'rear' move to insert in a circular queue?

    In a circular queue, the 'rear' moves to the next position using the formula 'rear = (rear + 1) % MAX_SIZE'. This accounts for wrapping around to the beginning of the array when the 'rear' reaches the end.

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    What is the output of this program?

    The output of the program is '2 1 8'. The code first initializes a LinkedList with elements 2, 8, 5, and 1. The 'reverse' function reverses the elements, followed by the 'shuffle' function, which randomizes their order. The iterator then removes the element and prints the remaining elements.

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    What does Collections.reverse(list) do?

    The 'Collections.reverse(list)' method reverses the order of elements within a list.

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    What does Collections.shuffle(list) do?

    The 'Collections.shuffle(list)' method randomly shuffles the order of elements within a list.

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    What is the purpose of binarySearch()?

    The 'binarySearch()' method efficiently searches for an element in a sorted list. Unlike linear search, it repeatedly divides the search space in half, making it significantly faster when dealing with large lists.

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    Study Notes

    Java Collection Framework Methods and Concepts

    • clear(): Deletes all elements from a collection.
    • Collections.emptySet(): Returns an immutable empty Set.
    • TreeMap: Sorts elements based on their natural ordering.
    • Vector: A dynamic array that can grow or shrink.
      • Vector(int initialCapacity, int capacityIncrement): Creates a Vector with a specified initial capacity and capacity increment.
      • capacity(): Returns the current capacity of the Vector.Example in the code shows a capacity of 4.
    • Map: Stores key-value associations.
    • LinkedList: A doubly linked list, allowing efficient insertion and deletion at any point.
      • iterator(): Returns an iterator over the elements of the LinkedList.
      • Collections.reverse(list): Reverses the order of elements in the LinkedList.
      • Collections.shuffle(list): Randomly shuffles the order of elements in the LinkedList.
    • ArrayList: A dynamic array that resizes as needed.
      • add(): Adds an element to the ArrayList.
      • ensureCapacity(int minCapacity): Increases the capacity of the ArrayList if necessary but doesn't add any element.
      • size(): Returns the number of elements in the list.
      • trimToSize(): Reduces the capacity of the ArrayList to match its actual size.
    • Arrays.sort(array): Sorts an array of int.
      • Arrays.binarySearch(array, value): Performs a binary search for a specified value in a sorted array.
    • Iterator: An object that allows traversal of elements in a collection.
      • hasNext(): Checks if there are more elements to traverse.
      • next(): Retrieves the next element.
      • remove(): Removes the last element returned by next().
    • LinkedList.removeFirst(): Removes and returns the first element from the LinkedList.
    • LinkedList.removeLast(): Removes and returns the last element from the LinkedList.
    • LinkedList.addFirst(): Adds an element to the start of the LinkedList.
    • LinkedList.set(index, element): Replaces the element at the specified index.
    • Vector.removeAll(Vector): Removes all elements that are present in the specified Vector from the original one.
    • Vector.insertElementAt(obj, index): Inserts an element at a specific index within the Vector.
    • Hashtable: A class that implements the Map interface, synchronised by default.
    • HashSet. add(): Adds an element to a HashSet.
    • Properties: A subclass of Hashtable designed to store properties.
      • keySet(): Returns a Set view of the keys contained in the Properties object.
    • BitSet: A specialized class for storing bits (boolean values).
      • get(index): Retrieves a bit at a specific index from the BitSet.
    • Collection: An interface that provides methods for manipulating collections in general.
    • SortedSet: An interface imposing an ordering on a set, TreeSet is one of its implementations.
      • TreeSet: A concrete class implementing SortedSet and storing elements sorted based on their natural order or a custom comparator.
      • SortedSet is an interface whereas TreeSet is a concrete class.
    • remove(): Removes a specific element in the ArrayList.
    • ObjectNotFoundException: Generic exception, IllegalStateException is a specific exception related to invalid iterator operations.

    Exception Handling in Collections

    • IllegalStateException: Can be thrown by the remove() method of an iterator if the next() method hasn't been called or if the remove method has already been called since the last call to next().

    Specific collection type details

    • HashSet: Stores unique elements, no order is guaranteed.
    • ArrayList: Ordered collection, elements are accessed using indexes, allows duplicates.
    • LinkedList: Ordered collection, elements are linked, provides efficient insertion and deletion at specific positions.
    • HashMap / Hashtable: Associative arrays, stores key-value pairs.
    • TreeMap: Ordered collection of keys and values. Sorts keys.

    Summary of Key Methods

    • find(): This method isn't available in the standard Java Collections Framework for searching. Use binarySearch for sorted lists or iterate for general search.
    • get(): Used to access elements by index in List implementations (e.g., ArrayList).
    • binarySearch(): Performs a binary search on a sorted array or list.
    • fill(): Used to set all elements of a list to the same value.
    • next(): Moves to the next element in an iterator.
    • add(): Used for adding elements to lists. remove() is for deleting elements.

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    Test your knowledge of the Java Collection Framework methods and concepts. This quiz covers essential functionalities such as clear(), TreeMap, Vector, and various collection types like Map and LinkedList. Perfect for anyone looking to solidify their understanding of Java collections.

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