Java Collections Framework Study Notes
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Questions and Answers

Which method is used to clear all the elements in a Hashtable?

  • delete()
  • removeAll()
  • clear() (correct)
  • reset()

What will be the maximum size of a List created using Arrays.asList()?

  • It is limited to 10 elements
  • It can only hold primitive data types
  • It can grow dynamically
  • It is fixed and cannot be altered (correct)

What is the output of calling the max() method with just a Comparator parameter?

  • It returns the maximum value based on the comparator
  • It returns the first element of the list
  • It throws an IllegalArgumentException
  • It requires a collection to function (correct)

Which collection type can be synchronized using Collections.synchronizedMap()?

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

What is the output of the following Java program involving a TreeSet with the elements {3, 9, 1, 4, 8}?

<p>[1, 3, 4, 8, 9] (A)</p> Signup and view all the answers

What is the purpose of the contains(Object o) method in the Set interface?

<p>To check if a specified element exists (C)</p> Signup and view all the answers

Which iterator type can be used specifically with List collections?

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

Which method retrieves the element at a specific location in a properties object?

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

What method is used to add a key-value pair to a map in Java?

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

What will be the output of the Java code that uses a stack to push and pop integer values?

<p>[3, 5] (C)</p> Signup and view all the answers

Which method is correctly used to randomize the elements in a list?

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

Which method can convert an ArrayList object to a static array?

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

When inserting a value and its key into a map, which method is used?

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

Which method removes all key-value pairs from a map?

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

What will be printed by the provided Java program that utilizes ListIterator if called on an empty list?

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

What does the Java program using reflection print about 'java.awt.Dimension'?

<p>Prints all the methods of 'java.awt.Dimension' (B)</p> Signup and view all the answers

What occurs when an existing key object is put into a HashMap?

<p>The new object replaces the older object (A)</p> Signup and view all the answers

What does the method peek() do in a collection?

<p>It returns the next item in line without removing it. (B)</p> Signup and view all the answers

Which method is used to retrieve the current size of an ArrayList object?

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

Which of the following is NOT a legacy class?

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

What is the initial capacity and load factor of a HashSet in Java?

<p>16, 0.75 (D)</p> Signup and view all the answers

What output will the Java program with the LinkedList produce?

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

In the provided HashSet example, what will be printed along with the size?

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

Does the HashSet class have a get(Object o) method?

<p>No, it does not allow retrieving by object. (B)</p> Signup and view all the answers

Which of the following collections implements a linked list data structure?

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

What will be the output of the HashSet example with added elements 'A', 'B', 'C'?

<p>[A, B, C] 3 (D)</p> Signup and view all the answers

What is the correct terminology for the collection of elements in a HashSet?

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

Flashcards

Stack pop() method

Removes and returns the element at the top of the stack.

List shuffle() method

Randomly reorders the elements in a list.

ArrayList toArray() method

Returns an array containing all the elements of the ArrayList.

HashMap put() method

Inserts a key-value pair into a HashMap.

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Map clear() method

Removes all key-value pairs from a map.

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ListIterator hasNext()

Checks if there are more elements in the list.

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Class.forName()

Returns the Class object for a given class.

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Class getMethods()

Returns all the public methods of a class.

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HashMap key replacement

If a key already exists, the new object replaces it.

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ListIterator previousIndex()

Gets the index of the element before the current position in iteration

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Synchronizing HashMap

Using Collections.synchronizedMap() to create a thread-safe HashMap.

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HashSet Implementation

HashSet uses HashMap internally to store elements.

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hasNext() Return Type

The hasNext() method of an iterator returns a boolean value (true or false).

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TreeSet Ordering

TreeSet automatically sorts elements in ascending order based on their natural ordering or a provided comparator.

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Arrays.fill() Usage

Used to replace elements in an array with a specific value within a range.

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Hashtable clear()

The clear() method removes all mappings from a Hashtable, making it empty.

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Properties.getProperty()

Retrieves a value from a Java Properties object using its key.

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HashMap.put()

Used to add a key-value pair to a HashMap.

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List Duplicates Removal

Using a HashSet to remove duplicate elements from a List (by converting it).

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ListIterator

An iterator specifically designed to work with Lists, allowing bidirectional traversal.

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ArrayList size()

Returns the number of elements in an ArrayList.

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LinkedList

An implementation of a linked list data structure.

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HashSet initial capacity

The initial size of a HashSet, default 16.

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C.dequeue() method

Removes and returns the next item in a queue.

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HashSet

A collection that stores unique elements, does not maintain order.

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Legacy classes

Older classes in Java, like Stack, Hashtable, and Vector.

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Iterator

Used to traverse elements in a collection.

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HashSet get(Object o)

Doesn't exist. HashSets do not support getting elements with specific object references.

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Queue dequeue()

Returns the next element in a Queue, and removes it from the Queue.

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Queue peek()

Returns the next element in a Queue without removing it.

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Study Notes

Java Collections Framework - Study Notes

  • Stack:

    • push(): Adds an element to the top of the stack.
    • pop(): Removes and returns the element at the top of the stack.
    • println(obj): Prints the stack elements as a string.
    • Output of import java.util.*; class stack { public static void main(String args[]) { Stack obj = new Stack(); obj.push(new Integer(3)); obj.push(new Integer(2)); obj.pop(); obj.push(new Integer(5)); System.out.println(obj); } } -> [3, 5]

  • List:

    • shuffle(): Randomizes the order of elements in a list.

  • ArrayList:

    • toArray(): Converts an ArrayList to a standard array.

  • HashMap:

    • put(): Inserts a key-value pair into the map.
    • If a key already exists, the new value replaces the older value.

  • Map:

    • clear(): Removes all key-value pairs from the map.

  • remove(): Removes a key-value pair from the map.

  • ListIterator:

    • listIterator(): Creates a ListIterator object.

  • java.awt.Dimension:

    • Class.forName("java.awt.Dimension"): Returns the class of Dimension.
    • c.getMethods(): retrieves all methods of that class.
    • Output of the following code: import java.lang.reflect.*; class Additional_packages { public static void main(String args[]) { try { Class c = Class.forName("java.awt.Dimension"); Method methods[] = c.getMethods(); for (int i = 0; i < methods.length; i++) System.out.println(methods[i]); } catch (Exception e) { System.out.print("Exception"); } } } -> prints all the methods of java.awt.Dimension

  • HashSet:

    • Implements HashMap internally.
    • contains(Object o): Checks if a set contains an object.
    • Example: HashSet obj = new HashSet(); obj.add("A"); obj.add("B"); obj.add("C"); System.out.println(obj + " " + obj.size()); outputs [A, B, C] 3

  • TreeSet:

    • Stores elements in a sorted order.
    • Output of import java.util.*; class Output { public static void main(String args[]) { TreeSet t = new TreeSet(); t.add("3"); t.add("9"); t.add("1"); t.add("4"); t.add("8"); System.out.println(t); } } -> [1, 3, 4, 8, 9]

  • Arrays:

    • Arrays.fill(): Fills a portion of an array with a specified value.
    • Example: import java.util.*; class Array { public static void main(String args[]) { int array[] = new int[5]; for (int i = 5; i > 0; i--) array[5-i] = i; Arrays.fill(array, 1, 4, 8); for (int i = 0; i < 5 ; i++) System.out.print(array[i]); } } -> 58881

  • LinkedList:

    • Iterator: An object used to traverse collection elements.
    • The while(i.hasNext()) loop iterates and prints the next element in the linked list.
    • Output of import java.util.*; class Collection_Algos { public static void main(String args[]) { LinkedList list = new LinkedList(); list.add(new Integer(2)); list.add(new Integer(8)); list.add(new Integer(5)); list.add(new Integer(1)); Iterator i = list.iterator(); while(i.hasNext()) System.out.print(i.next() + " "); } }-> 2 8 5 1

  • Collections:

    • synchronizedMap(new HashMap()): Creates a thread-safe HashMap.

  • Iterator:

    • hasNext(): Checks if there are more elements in the iteration. Returns a boolean.

  • List:

    • ListIterator is specific to List interface; used to traverse elements in a specific order of the List.

  • Arrays.asList():

    • Returns a fixed-size list backed by the specified array. Modifying the returned list directly affects the original array.

  • Dequeue/Peek:

    • dequeue(): Removes and returns the first element in the queue;
    • peek(): Returns the first element in the queue without removing it.

  • Properties:

    • getProperty(): Retrieves a property value from a Properties object.

  • List manipulation: - To remove duplicates from a List, use a HashSet to store the unique elements (since a HashSet doesn't allow duplicates).

  • General Note: The Java Collections Framework provides a set of classes and interfaces for working with collections of objects, offering various functionalities like insertion, removal, traversal, searching, sorting, etc, and the legacy classes are older (Stack, Hashtable, Vector) classes that might have different structure and design compared to the current classes.

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Description

Explore the essential concepts of the Java Collections Framework, covering components like Stack, List, ArrayList, and HashMap. Understand key methods such as push, pop, shuffle, and put, along with their functionalities. This quiz is designed to test your knowledge and understanding of Java's powerful data structures.

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