Java Collection Framework for BCA Students

Java Collection Framework for BCA Students

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  Collection Frameworks inJava 8.0 Collection Framework in Java 8 The Collection Framework in Java 8 is a unified architecture that provides a set of interfaces and classes for storing, processing, and manipulating collections of objects. It simplifies the handling of data structures like lists, sets, and maps while improving performance and reusability. Categories of Collection Framework Java Collection Framework is divided into the following categories: 1. List Interface (Ordered collection, allows duplicates) o Classes: ArrayList, LinkedList, Vector, Stack 2. Set Interface (Unordered collection, no duplicates) o Classes: HashSet, LinkedHashSet, TreeSet 3. Queue Interface (FIFO or priority-based ordering) o Classes: PriorityQueue, ArrayDeque 4. Map Interface (Key-value pairs, unique keys) o Classes: HashMap, LinkedHashMap, TreeMap, Hashtable Available Classes and Interfaces in Collection Framework Interfaces  Collection  List  Set  Queue, Deque  Map  SortedSet  SortedMap Classes 1. ArrayList, LinkedList, Vector, Stack 2. HashSet, LinkedHashSet, TreeSet 3. PriorityQueue, ArrayDeque 4. HashMap, LinkedHashMap, TreeMap, Hashtable
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  Collection Frameworks inJava 8.0 List Interface Example: ArrayList import java.util.ArrayList; public class ArrayListExample { public static void main(String[] args) { ArrayList<String> names = new ArrayList<>(); names.add("John"); names.add("Emma"); names.add("Oliver"); System.out.println("ArrayList elements: " + names); // Retrieving an element System.out.println("First element: " + names.get(0)); // Removing an element names.remove("Emma"); System.out.println("After removing Emma: " + names); } } Explanation  Creates an ArrayList of String type.  Adds elements using add().  Retrieves an element using get().  Removes an element using remove(). Expected Output ArrayList elements: [John, Emma, Oliver] First element: John After removing Emma: [John, Oliver] Real-time Usage Used in dynamic arrays where random access is required, such as storing a list of student names in an application. Set Interface Example: HashSet import java.util.HashSet; public class HashSetExample { public static void main(String[] args) { HashSet<Integer> numbers = new HashSet<>(); numbers.add(10);
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  Collection Frameworks inJava 8.0 numbers.add(20); numbers.add(30); numbers.add(10); // Duplicate will be ignored System.out.println("HashSet elements: " + numbers); } } Explanation  Creates a HashSet that stores unique integers.  Adds duplicate element 10, but it is ignored. Expected Output HashSet elements: [10, 20, 30] Real-time Usage  Used in scenarios where duplicate values must be avoided, like storing unique customer IDs. Queue Interface Example: PriorityQueue import java.util.PriorityQueue; public class PriorityQueueExample { public static void main(String[] args) { PriorityQueue<Integer> pq = new PriorityQueue<>(); pq.add(30); pq.add(10); pq.add(20); System.out.println("PriorityQueue elements: " + pq); System.out.println("Poll (removes highest priority element): " + pq.poll()); System.out.println("Updated PriorityQueue: " + pq); } } Explanation  PriorityQueue sorts elements in natural order.  poll() removes the smallest element (highest priority). Expected Output PriorityQueue elements: [10, 30, 20] Poll (removes highest priority element): 10
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  Collection Frameworks inJava 8.0 Updated PriorityQueue: [20, 30] Real-time Usage  Used in task scheduling (e.g., CPU process scheduling). Map Interface Example: HashMap import java.util.HashMap; public class HashMapExample { public static void main(String[] args) { HashMap<Integer, String> empMap = new HashMap<>(); empMap.put(101, "John"); empMap.put(102, "Emma"); empMap.put(103, "Oliver"); System.out.println("HashMap: " + empMap); System.out.println("Value for key 102: " + empMap.get(102)); empMap.remove(101); System.out.println("After removing key 101: " + empMap); } } Explanation  HashMap stores key-value pairs.  put() adds entries, get() retrieves values, and remove() deletes an entry. Expected Output HashMap: {101=John, 102=Emma, 103=Oliver} Value for key 102: Emma After removing key 101: {102=Emma, 103=Oliver} Real-time Usage  Used in applications like maintaining employee records in an HR system. Conclusion Java 8 Collection Framework provides powerful data structures to handle and manipulate data efficiently. Each class serves a unique purpose in real-world scenarios, such as:  ArrayList for dynamic lists.  HashSet for unique elements.  PriorityQueue for task scheduling.  HashMap for key-value storage.
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  Collection Frameworks inJava 8.0 Vector Class in Java Collection Framework The Vector class in Java is a part of the java.util package and implements the List interface. It is similar to an ArrayList but is synchronized, making it thread-safe. This makes it a good choice for multi-threaded applications where multiple threads might access the same collection. Key Features of Vector  Dynamic Array: Grows dynamically as elements are added.  Thread-Safety: Methods like add(), remove(), and get() are synchronized.  Allows Duplicates: Unlike Set, Vector allows duplicate elements.  Random Access: Supports fast retrieval of elements using an index.  Enumeration & Iterator Support: It supports both Iterator and Enumeration to traverse elements. Real-Time Use Case: Managing an Online Course Student List Let’s consider a scenario where an online course needs to store a list of students enrolled in a course. Since multiple threads (like admin and students) might access or modify this list, a synchronized list (Vector) ensures thread safety. Java Program: Implementing Vector Class import java.util.Vector; import java.util.Iterator; public class VectorExample { public static void main(String[] args) { // Creating a Vector to store student names Vector<String> studentList = new Vector<>(); // Adding elements to the Vector studentList.add("John"); studentList.add("Emma"); studentList.add("Michael"); studentList.add("Sarah"); // Displaying the Vector System.out.println("Student List: " + studentList); // Adding a new student at index 2 studentList.add(2, "David"); System.out.println("After adding 'David' at index 2: " + studentList); // Removing a student studentList.remove("Emma"); System.out.println("After removing 'Emma': " + studentList);
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  Collection Frameworks inJava 8.0 // Retrieving an element System.out.println("Student at index 1: " + studentList.get(1)); // Iterating through the Vector using an Iterator System.out.println("Iterating through the student list:"); Iterator<String> itr = studentList.iterator(); while (itr.hasNext()) { System.out.println(itr.next()); } // Checking if a student exists in the Vector System.out.println("Is 'John' in the list? " + studentList.contains("John")); } } Explanation of Code 1. Creating a Vector<String>: o Vector<String> studentList = new Vector<>(); creates a Vector to store student names. 2. Adding Elements: o add("John"), add("Emma"), etc., add students to the list. o add(2, "David") adds a student at a specific position. 3. Removing Elements: o remove("Emma") removes "Emma" from the list. 4. Retrieving Elements: o get(1) retrieves the student at index 1. 5. Iterating Through the Vector: o Uses an Iterator to print all elements. 6. Checking for an Element: o contains("John") checks if "John" is in the list. Expected Output Student List: [John, Emma, Michael, Sarah] After adding 'David' at index 2: [John, Emma, David, Michael, Sarah] After removing 'Emma': [John, David, Michael, Sarah] Student at index 1: David Iterating through the student list: John David Michael Sarah Is 'John' in the list? true
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  Collection Frameworks inJava 8.0 Real-Time Use Case Scenario: Managing an Online Course Enrollment System  The admin panel can add or remove students.  A Vector ensures thread safety when multiple users (admin and students) access the list.  Fast retrieval of students based on their enrollment order.  Duplicate student names allowed but can be controlled using contains(). Conclusion  The Vector class is useful for applications where: ✅ Thread safety is required.  Frequent modifications (adding/removing elements) occur.  Random access to elements is needed. Hashtable Class in Java Collection Framework The Hashtable class in Java is a part of the java.util package and implements the Map interface. It is used to store key-value pairs, similar to HashMap, but with one key difference—it is synchronized, meaning it is thread-safe. Key Features of Hashtable  Stores Key-Value Pairs: Each key in a Hashtable is unique and maps to a specific value.  Thread-Safe: All methods are synchronized, making it suitable for multi-threaded environments.  Does Not Allow Null Keys or Values: Unlike HashMap, Hashtable does not permit null keys or null values.  Maintains No Order: Elements are stored based on their hash codes, and the order may not be predictable.  Performance: Slightly slower than HashMap due to synchronization. Real-Time Use Case: Employee Directory in a Company A company wants to store employee details (ID and Name) in a system that multiple users (HR, Manager, Employees) access simultaneously. Since multiple users might read or update this data, a thread-safe collection like Hashtable is the best choice. Java Program: Implementing Hashtable import java.util.Hashtable; import java.util.Enumeration; public class HashtableExample { public static void main(String[] args) { // Creating a Hashtable to store Employee ID and Name Hashtable<Integer, String> employeeTable = new Hashtable<>();
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  Collection Frameworks inJava 8.0 // Adding elements to the Hashtable employeeTable.put(101, "John"); employeeTable.put(102, "Emma"); employeeTable.put(103, "Oliver"); employeeTable.put(104, "Sophia"); // Displaying the Hashtable System.out.println("Employee Directory: " + employeeTable); // Retrieving a value using a key System.out.println("Employee with ID 102: " + employeeTable.get(102)); // Checking if a key exists System.out.println("Is Employee ID 105 present? " + employeeTable.containsKey(105)); // Checking if a value exists System.out.println("Is 'Sophia' in the directory? " + employeeTable.containsValue("Sophia")); // Removing an entry from the Hashtable employeeTable.remove(103); System.out.println("After removing Employee ID 103: " + employeeTable); // Iterating through the Hashtable using Enumeration System.out.println("Iterating through Employee Directory:"); Enumeration<Integer> keys = employeeTable.keys(); while (keys.hasMoreElements()) { Integer key = keys.nextElement(); System.out.println("ID: " + key + ", Name: " + employeeTable.get(key)); } } } Explanation of Code 1. Creating a Hashtable<Integer, String>: o Hashtable<Integer, String> employeeTable = new Hashtable<>(); creates a Hashtable to store Employee ID (Integer) as the key and Employee Name (String) as the value. 2. Adding Elements: o put(101, "John"), etc., stores employee details. 3. Retrieving an Element: o get(102) retrieves the name of employee with ID 102. 4. Checking for a Key or Value: o containsKey(105) checks if employee ID 105 exists.
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  Collection Frameworks inJava 8.0 o containsValue("Sophia") checks if "Sophia" exists in the list. 5. Removing an Entry: o remove(103) deletes the entry for Employee ID 103. 6. Iterating Through the Hashtable: o Uses Enumeration to loop through all elements. Expected Output Employee Directory: {101=John, 102=Emma, 103=Oliver, 104=Sophia} Employee with ID 102: Emma Is Employee ID 105 present? false Is 'Sophia' in the directory? true After removing Employee ID 103: {101=John, 102=Emma, 104=Sophia} Iterating through Employee Directory: ID: 101, Name: John ID: 102, Name: Emma ID: 104, Name: Sophia Real-Time Use Case Scenario: Employee Directory in a Multi-User HR System  HR Department, Managers, and Employees need access to employee data.  A Hashtable ensures thread safety when multiple users simultaneously access or modify the employee database.  Fast lookups allow retrieving employee details quickly.  No null values prevent accidental missing data. Comparison: Hashtable vs. HashMap Feature Hashtable HashMap Thread Safety Yes (synchronized) No (not synchronized) Null Keys/Values Not Allowed Allowed Performance Slower due to synchronization Faster Use Case Multi-threaded applications General-purpose collections Conclusion The Hashtable class is an excellent choice when:  Thread safety is required.  Fast lookup operations (key-value pairs) are needed.  Null keys/values should be avoided (e.g., Employee ID system). LinkedList Class in Java Collection Framework The LinkedList class in Java is part of the java.util package and implements the List and Deque interfaces. It is a doubly linked list that allows fast insertions and deletions compared to ArrayList, making it a great choice for applications requiring frequent modifications.
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  Collection Frameworks inJava 8.0 Key Features of LinkedList  Doubly Linked List Implementation: Each node has references to both its previous and next nodes.  Efficient Insertions/Deletions: Faster than ArrayList for adding/removing elements in the middle.  Allows Duplicates & Null Elements: Unlike Set, it allows duplicate elements.  Can Be Used as a List, Queue, or Deque: Implements List, Queue, and Deque interfaces.  Maintains Insertion Order: Elements are stored in the order they were added. Real-Time Use Case: Train Ticket Reservation System A train ticket reservation system needs to maintain a waiting list of passengers. Since passengers might cancel their bookings, removing an element from the middle of the list should be fast. LinkedList is ideal for this scenario because of its efficient insertion and deletion operations. Java Program: Implementing LinkedList import java.util.LinkedList; import java.util.Iterator; public class LinkedListExample { public static void main(String[] args) { // Creating a LinkedList to store passenger names LinkedList<String> waitingList = new LinkedList<>(); // Adding elements to the LinkedList waitingList.add("Alice"); waitingList.add("Bob"); waitingList.add("Charlie"); waitingList.add("David"); // Displaying the LinkedList System.out.println("Initial Waiting List: " + waitingList); // Adding a passenger at the beginning waitingList.addFirst("Zara"); System.out.println("After adding 'Zara' at the beginning: " + waitingList); // Adding a passenger at the end waitingList.addLast("Ethan"); System.out.println("After adding 'Ethan' at the end: " + waitingList); // Removing a passenger from the middle waitingList.remove("Charlie");
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  Collection Frameworks inJava 8.0 System.out.println("After removing 'Charlie': " + waitingList); // Checking the first and last passenger System.out.println("First passenger in waiting list: " + waitingList.getFirst()); System.out.println("Last passenger in waiting list: " + waitingList.getLast()); // Iterating through the LinkedList using an Iterator System.out.println("Iterating through the waiting list:"); Iterator<String> itr = waitingList.iterator(); while (itr.hasNext()) { System.out.println(itr.next()); } // Checking if a passenger is on the list System.out.println("Is 'Alice' on the waiting list? " + waitingList.contains("Alice")); } } Explanation of Code 1. Creating a LinkedList<String>: o LinkedList<String> waitingList = new LinkedList<>(); creates a list for passenger names. 2. Adding Elements: o add("Alice"), add("Bob"), etc., add passengers to the waiting list. o addFirst("Zara") adds a passenger at the beginning. o addLast("Ethan") adds a passenger at the end. 3. Removing Elements: o remove("Charlie") removes a specific passenger. 4. Retrieving First and Last Elements: o getFirst() retrieves the first passenger. o getLast() retrieves the last passenger. 5. Iterating Through the LinkedList: o Uses an Iterator to print all elements. 6. Checking for a Passenger: o contains("Alice") checks if "Alice" is on the list. Expected Output Initial Waiting List: [Alice, Bob, Charlie, David] After adding 'Zara' at the beginning: [Zara, Alice, Bob, Charlie, David] After adding 'Ethan' at the end: [Zara, Alice, Bob, Charlie, David, Ethan] After removing 'Charlie': [Zara, Alice, Bob, David, Ethan]
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  Collection Frameworks inJava 8.0 First passenger in waiting list: Zara Last passenger in waiting list: Ethan Iterating through the waiting list: Zara Alice Bob David Ethan Is 'Alice' on the waiting list? true Real-Time Use Case Scenario: Train Ticket Reservation System  A LinkedList is used to maintain a waiting list of passengers.  If a passenger cancels, removing them from the list is efficient.  New passengers can be added at the beginning or end as required.  Maintaining order is important for FIFO (First-In-First-Out) processing. Comparison: LinkedList vs. ArrayList Feature LinkedList ArrayList Implementation Doubly Linked List Dynamic Array Insertion/Deletion Faster (O(1) at start/middle) Slower (O(n) for middle) Random Access Slower (O(n)) Faster (O(1)) Memory Usage Higher (extra node references) Lower Best Use Case Frequent insertions/removals Frequent random access The LinkedList class is best when:  Frequent insertions and deletions are needed.  FIFO (First-In-First-Out) processing is required.  Order must be maintained, such as in waiting lists, history logs, and undo operations. SortedSet Interface in Java The SortedSet interface in Java is part of the java.util package and extends the Set interface. It provides a way to store unique elements in a sorted order. Key Features of SortedSet  No Duplicates: Like Set, it does not allow duplicate elements.  Sorted Order: Elements are sorted in natural order (ascending for numbers, alphabetical for strings).  Implements NavigableSet: The main implementation of SortedSet is TreeSet, which also implements NavigableSet.  Retrieval Methods: o first() – Returns the first (lowest) element.
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  Collection Frameworks inJava 8.0 o last() – Returns the last (highest) element. o headSet(E element) – Returns elements before the given element. o tailSet(E element) – Returns elements after or equal to the given element. o subSet(E fromElement, E toElement) – Returns a range of elements. Real-Time Use Case: Student Roll Numbers in a School A school wants to store student roll numbers in sorted order and ensure there are no duplicates. SortedSet is the best choice because:  The roll numbers are stored in ascending order automatically.  Duplicate roll numbers are not allowed.  The first and last roll numbers can be retrieved easily. Java Program: Implementing SortedSet Using TreeSet import java.util.SortedSet; import java.util.TreeSet; public class SortedSetExample { public static void main(String[] args) { // Creating a SortedSet (TreeSet) to store student roll numbers SortedSet<Integer> rollNumbers = new TreeSet<>(); // Adding roll numbers to the SortedSet rollNumbers.add(105); rollNumbers.add(101); rollNumbers.add(108); rollNumbers.add(103); rollNumbers.add(102); // Displaying the SortedSet System.out.println("Sorted Roll Numbers: " + rollNumbers); // Getting the first and last elements System.out.println("First Roll Number: " + rollNumbers.first()); System.out.println("Last Roll Number: " + rollNumbers.last()); // Getting elements before a specific roll number System.out.println("Roll numbers before 105: " + rollNumbers.headSet(105)); // Getting elements from a specific roll number onwards System.out.println("Roll numbers from 103 onwards: " + rollNumbers.tailSet(103));
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  Collection Frameworks inJava 8.0 // Getting a range of roll numbers System.out.println("Roll numbers between 102 and 108: " + rollNumbers.subSet(102, 108)); // Trying to add a duplicate roll number (ignored) rollNumbers.add(101); System.out.println("After adding duplicate 101: " + rollNumbers); } } Explanation of Code 1. Creating a SortedSet<Integer>: o SortedSet<Integer> rollNumbers = new TreeSet<>(); creates a sorted set for storing roll numbers. 2. Adding Elements: o add(105), add(101), etc., adds roll numbers (in an unsorted manner). 3. Automatic Sorting: o TreeSet automatically sorts roll numbers in ascending order. 4. Retrieving First and Last Elements: o first() returns the smallest roll number. o last() returns the largest roll number. 5. Retrieving Subsets of Elements: o headSet(105) returns roll numbers less than 105. o tailSet(103) returns roll numbers from 103 onwards. o subSet(102, 108) returns roll numbers from 102 (inclusive) to 108 (exclusive). 6. Duplicate Handling: o add(101) attempts to add a duplicate roll number, but SortedSet ignores it. Expected Output Sorted Roll Numbers: [101, 102, 103, 105, 108] First Roll Number: 101 Last Roll Number: 108 Roll numbers before 105: [101, 102, 103] Roll numbers from 103 onwards: [103, 105, 108] Roll numbers between 102 and 108: [102, 103, 105] After adding duplicate 101: [101, 102, 103, 105, 108] Real-Time Use Case Scenario: Student Roll Number Management  A school database needs to maintain a sorted list of student roll numbers.  Ensures unique roll numbers (no duplicates).  Automatically sorts roll numbers when a new student is added.  Fast retrieval of roll numbers within a range (e.g., students in a specific class).
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  Collection Frameworks inJava 8.0 Comparison: SortedSet vs. HashSet vs. TreeSet Feature SortedSet (TreeSet) HashSet LinkedHashSet Order Sorted (Natural Order) Unordered Insertion Order Duplicates Not Allowed Not Allowed Not Allowed Performance Slower (O(log n)) Fast (O(1)) Moderate (O(1)) Use Case Sorted, Unique Data Unique, Fast Lookup Ordered Unique Data Conclusion The SortedSet (implemented as TreeSet) is best when:  Data must be sorted automatically (e.g., Student Roll Numbers).  Duplicate values should not be allowed.  Efficient range queries (subSet, headSet, tailSet) are required. Stack Class in Java Collection Framework The Stack class in Java is a Last In, First Out (LIFO) data structure. It extends Vector, meaning it has all the properties of a dynamic array while providing additional stack-specific methods. Key Features of Stack  Follows LIFO (Last In, First Out): The last element added is the first to be removed.  Implements push() and pop() Methods: o push(E item): Adds an item to the top of the stack. o pop(): Removes and returns the top item from the stack. o peek(): Returns the top element without removing it. o isEmpty(): Checks if the stack is empty. o search(E item): Returns the 1-based position of an element in the stack. Real-Time Use Case: Web Browser Back Button A web browser uses a stack to keep track of visited web pages.  When the user visits a new webpage, it is pushed onto the stack.  When the user clicks the Back button, the most recent page is popped from the stack, taking the user to the previous page. Java Program: Implementing Stack in a Web Browser Back Navigation import java.util.Stack; public class StackExample { public static void main(String[] args) {
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  Collection Frameworks inJava 8.0 // Creating a Stack to store browser history Stack<String> browserHistory = new Stack<>(); // Pushing webpages onto the stack browserHistory.push("Google.com"); browserHistory.push("Facebook.com"); browserHistory.push("YouTube.com"); browserHistory.push("StackOverflow.com"); // Displaying the Stack System.out.println("Current Browser History: " + browserHistory); // Getting the current page (Top of the Stack) System.out.println("Current Page: " + browserHistory.peek()); // Going Back (Popping the top page) System.out.println("Going Back from: " + browserHistory.pop()); System.out.println("Now on Page: " + browserHistory.peek()); // Checking if Stack is empty System.out.println("Is browser history empty? " + browserHistory.isEmpty()); // Searching for a website in history System.out.println("Position of 'Google.com' in history: " + browserHistory.search("Google.com")); } } Explanation of Code 1. Creating a Stack<String>: o Stack<String> browserHistory = new Stack<>(); creates a stack to store webpage URLs. 2. Adding Web Pages (Pushing to Stack): o push("Google.com"), push("Facebook.com"), etc., add pages to the history stack. 3. Checking the Current Page (peek()): o peek() returns the last visited page (top of the stack). 4. Going Back (pop()): o pop() removes the most recent page, simulating the Back button. 5. Checking Stack Status (isEmpty()): o isEmpty() checks if there are any more pages left in history. 6. Searching for a Page (search()):
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  Collection Frameworks inJava 8.0 o search("Google.com") finds the position of Google.com in the history stack. Expected Output Current Browser History: [Google.com, Facebook.com, YouTube.com, StackOverflow.com] Current Page: StackOverflow.com Going Back from: StackOverflow.com Now on Page: YouTube.com Is browser history empty? false Position of 'Google.com' in history: 3 Real-Time Use Case Scenario: Undo Feature in Text Editors A stack is used in text editors to implement Undo functionality:  Every change made to a document is pushed onto the stack.  When the user presses Ctrl + Z, the last change is popped from the stack, restoring the previous state. Comparison: Stack vs. Queue vs. Deque Feature Stack (LIFO) Queue (FIFO) Deque (Both Ends) Insertion push() (Top) offer() (End) offerFirst() / offerLast() Deletion pop() (Top) poll() (Front) pollFirst() / pollLast() Access Order Last In, First Out (LIFO) First In, First Out (FIFO) Both Ends Use Case Undo, Browser History Task Scheduling Double-ended processing Conclusion The Stack class is best when:  Data must be processed in LIFO order (e.g., Browser History, Undo feature).  Pushing and popping elements is frequent.  Search and retrieval of the top element are needed. Queue Interface in Java Collection Framework The Queue interface in Java is part of the java.util package and follows the First In, First Out (FIFO) principle. It is used to store elements sequentially, where the element added first is processed first.
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  Collection Frameworks inJava 8.0 Key Features of Queue  FIFO (First In, First Out): The first element inserted is the first to be removed.  Different Implementations: o LinkedList (Doubly Linked List-based Queue) o PriorityQueue (Sorted Order Queue) o ArrayDeque (Efficient Double-ended Queue)  Queue Methods: o offer(E e): Adds an element to the queue. o poll(): Removes and returns the head (first) element. o peek(): Returns the head element without removing it. o isEmpty(): Checks if the queue is empty. Real-Time Use Case: Customer Service Ticket System A customer support center uses a queue to handle service requests.  New customer requests are added to the queue.  Requests are processed in order (First Come, First Served).  When an agent is available, the first request is handled. Java Program: Implementing Queue in a Customer Service System import java.util.LinkedList; import java.util.Queue; public class QueueExample { public static void main(String[] args) { // Creating a Queue to store customer service requests Queue<String> customerQueue = new LinkedList<>(); // Adding customer requests (enqueue) customerQueue.offer("Customer 1 - Billing Issue"); customerQueue.offer("Customer 2 - Technical Support"); customerQueue.offer("Customer 3 - Account Upgrade"); // Displaying the Queue System.out.println("Customer Queue: " + customerQueue); // Processing customers (dequeue) System.out.println("Processing: " + customerQueue.poll()); // Removes Customer 1 System.out.println("Next in Queue: " + customerQueue.peek()); // Shows Customer 2 // Processing another customer System.out.println("Processing: " + customerQueue.poll()); // Removes Customer 2
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  Collection Frameworks inJava 8.0 // Checking if the queue is empty System.out.println("Is the queue empty? " + customerQueue.isEmpty()); // Displaying remaining queue System.out.println("Remaining Queue: " + customerQueue); } } Explanation of Code 1. Creating a Queue<String>: o Queue<String> customerQueue = new LinkedList<>(); creates a queue for customer service requests. 2. Adding Customers (offer()): o offer("Customer 1 - Billing Issue") adds a customer request to the queue. 3. Processing Customers (poll()): o poll() removes the first request (head of the queue). 4. Checking the Next Customer (peek()): o peek() retrieves the first element without removing it. 5. Checking Queue Status (isEmpty()): o isEmpty() checks if any customers are waiting. Expected Output: Customer Queue: [Customer 1 - Billing Issue, Customer 2 - Technical Support, Customer 3 - Account Upgrade] Processing: Customer 1 - Billing Issue Next in Queue: Customer 2 - Technical Support Processing: Customer 2 - Technical Support Is the queue empty? false Remaining Queue: [Customer 3 - Account Upgrade] Real-Time Use Case Scenario: Task Scheduling in CPU Operating systems use queues for task scheduling:  Processes waiting for CPU execution are stored in a queue.  The CPU executes the first process in the queue.  After execution, the next process is taken from the queue. Comparison: Queue vs. Stack vs. Deque Feature Queue (FIFO) Stack (LIFO) Deque (Both Ends) Insertion offer() (End) push() (Top) offerFirst() / offerLast() Deletion poll() (Front) pop() (Top) pollFirst() / pollLast()
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  Collection Frameworks inJava 8.0 Processing Order First In, First Out (FIFO) Last In, First Out (LIFO) Both Ends Use Case Task Scheduling, Customer Service Undo, Browser History Double-ended processing Conclusion The Queue interface is best when:  Data must be processed in FIFO order (e.g., Customer Service, Task Scheduling).  Efficient element retrieval from the front is required.  Handling requests in order is important. Map Interface in Java Collection Framework The Map interface in Java is part of the java.util package and is used to store key-value pairs. Unlike List or Set, a Map does not allow duplicate keys. Key Features of Map  Stores key-value pairs (key -> value).  Keys must be unique, but values can be duplicate.  Efficient searching, insertion, and deletion using keys.  Common Implementations: o HashMap – Unordered, fast lookup. o LinkedHashMap – Maintains insertion order. o TreeMap – Sorted order (ascending by default). Real-Time Use Case: Student Database System A Map can be used to store student records where:  Student ID (Key) is unique.  Student Name (Value) stores the student’s name. Java Program: Implementing Map in a Student Database import java.util.HashMap; import java.util.Map; public class MapExample { public static void main(String[] args) { // Creating a Map to store Student ID -> Student Name Map<Integer, String> studentMap = new HashMap<>(); // Adding students (Key -> Value) studentMap.put(101, "Alice"); studentMap.put(102, "Bob"); studentMap.put(103, "Charlie"); studentMap.put(104, "David");
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  Collection Frameworks inJava 8.0 // Displaying the Student Map System.out.println("Student Records: " + studentMap); // Fetching a student's name using their ID System.out.println("Student with ID 102: " + studentMap.get(102)); // Checking if a student ID exists System.out.println("Is ID 105 present? " + studentMap.containsKey(105)); // Removing a student record studentMap.remove(103); System.out.println("After removing student 103: " + studentMap); // Iterating through the Map System.out.println("All Students:"); for (Map.Entry<Integer, String> entry : studentMap.entrySet()) { System.out.println("ID: " + entry.getKey() + ", Name: " + entry.getValue()); } } } Explanation of Code 1. Creating a Map<Integer, String>: o Map<Integer, String> studentMap = new HashMap<>(); creates a HashMap to store student records. 2. Adding Entries (put()): o put(101, "Alice") stores ID 101 -> Alice. 3. Fetching a Value (get()): o get(102) returns the student name "Bob". 4. Checking Key Existence (containsKey()): o containsKey(105) checks if ID 105 exists. 5. Removing an Entry (remove()): o remove(103) removes Charlie’s record. 6. Iterating Through Map (entrySet()): o for (Map.Entry<Integer, String> entry : studentMap.entrySet()) prints all ID -> Name pairs.
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  Collection Frameworks inJava 8.0 Expected Output Student Records: {101=Alice, 102=Bob, 103=Charlie, 104=David} Student with ID 102: Bob Is ID 105 present? false After removing student 103: {101=Alice, 102=Bob, 104=David} All Students: ID: 101, Name: Alice ID: 102, Name: Bob ID: 104, Name: David Real-Time Use Cases 1. Employee Payroll System  Key → Employee ID  Value → Employee Salary 2. Caching in Web Applications  Key → URL  Value → Cached Page Data 3. Inventory Management  Key → Product ID  Value → Quantity in Stock Comparison of Map Implementations Implementation Ordering Performance Null Keys & Values HashMap No Order Fast O(1) 1 Null Key, Multiple Null Values LinkedHashMap Insertion Order Slower than HashMap Supports Null TreeMap Sorted Order O(log N) No Null Keys, Supports Null Values Conclusion The Map interface is best when: o You want to store unique keys mapped to values. o You need different implementations for sorting or insertion order.