Java TreeSet Implementation and Custom Sorting

📘 Java Learning – Collections Framework (Final Part: Collections Class & Arrays Class) 🚀🎯 Wrapping up my Java Collections journey with two powerful utility classes from java.util package: 👉 Collections class 👉 Arrays class These classes provide utility methods for sorting, searching, reversing, and converting data structures efficiently. 🔰 Collections Class A utility class that provides methods for Collection implemented classes. 📌 Sorting a List Collections.sort(List l); // Natural sorting Collections.sort(List l, Comparator c); // Custom sorting ✔ Elements must be homogeneous & Comparable (for natural sorting) ✔ Null elements not allowed (NullPointerException) 📌 Searching in a List Collections.binarySearch(List l, Object obj); Collections.binarySearch(List l, Object key, Comparator c); ⚠ Important Rules: • List must be sorted before searching • Uses Binary Search algorithm • Successful search → returns index • Unsuccessful search → returns insertion point • Must use same Comparator used for sorting 📌 Reversing a List Collections.reverse(List l); // Reverses list Collections.reverseOrder(); // Returns Comparator (descending) ✔ reverse() → works on List ✔ reverseOrder() → returns Comparator 🔰 Arrays Class Utility class for array operations (primitive & object arrays). 📌 Sorting Arrays Arrays.sort(int[] arr); // Primitive (natural order) Arrays.sort(Object[] arr); // Natural order Arrays.sort(Object[] arr, Comparator c); // Custom sorting ✔ Primitive arrays → only natural sorting ✔ Object arrays → natural or custom sorting 📌 Searching in Arrays Arrays.binarySearch(int[] arr, key); Arrays.binarySearch(Object[] arr, key); Arrays.binarySearch(Object[] arr, key, Comparator c); ✔ Same rules as Collections.binarySearch() 🔰 Converting Array to List List list = Arrays.asList(Object[] arr); ⚠ Important: • Creates a List view, not independent list • Changes in list reflect in array & vice versa • Cannot change size (add/remove → UnsupportedOperationException) • Replacement allowed but type must match (else ArrayStoreException) 🧪 Combined Example Integer[] arr = {30, 10, 20}; Arrays.sort(arr); // Sorting array System.out.println(Arrays.toString(arr)); // [10, 20, 30] int index = Arrays.binarySearch(arr, 20); System.out.println(index); // 1 List list = Arrays.asList(arr); Collections.reverse(list); System.out.println(list); // [30, 20, 10] ⭐ Final Takeaways • Collections → Utility methods for List • Arrays → Utility methods for Arrays • Always sort before binarySearch • asList() creates a fixed-size list view This completes my Java Collections Framework journey 🎯 Understanding these utilities makes data handling more efficient and interview-ready 💡 Building strong Java fundamentals, one collection at a time ☕💻 #Java #CoreJava #CollectionsFramework #CollectionsClass #ArraysClass #JavaCollections #LearningJourney

 Day 7 – Queue, Deque & PriorityQueue in Java Collections (Backend Developer Learning Series) Today I revised Queue, Deque, and PriorityQueue from the Java Collection Framework — important data structures used in task scheduling, message queues, and backend processing systems. 📌 What is Queue? Queue is a sub-interface of Collection defined in the java.util package. Queue follows the FIFO principle (First In First Out). ➡ Elements are inserted from the rear (tail) ➡ Elements are removed from the front (head) Example: Insert → 10 20 30 40 Remove → 10 (first inserted element) ⚙ Queue Implementations Some commonly used Queue classes: ✔ LinkedList ✔ PriorityQueue ✔ ArrayDeque 📌 Important Queue Methods 1️⃣ offer() q.offer(40); Adds an element to the rear of the queue. 2️⃣ poll() q.poll(); Removes and returns the head element. 3️⃣ peek() q.peek(); Returns the head element without removing it. 📌 What is Deque? Deque stands for Double Ended Queue. It allows insertion and deletion from both ends. ✔ Insert from front and rear ✔ Remove from front and rear Deque is defined in java.util package. ⚙ Deque Implementations ✔ ArrayDeque ✔ LinkedList 📌 Important Deque Methods Insert Methods offerFirst() offerLast() addFirst() addLast() Remove Methods pollFirst() pollLast() removeFirst() removeLast() Access Methods peekFirst() peekLast() getFirst() getLast() 📌 ArrayDeque ArrayDeque is a class that implements the Deque interface. Key Points ✔ Introduced in JDK 1.6 ✔ Uses resizable array internally ✔ Faster than Stack in many cases ✔ Default capacity = 16 📌 PriorityQueue PriorityQueue is another implementation of the Queue interface. Unlike normal queues, elements are ordered based on priority instead of insertion order. ✔ Default sorting → Natural order (Ascending) ✔ Uses Heap data structure internally ✔ Does NOT allow null values 💻 Example Program – PriorityQueue import java.util.*; public class PriorityQueueExample { public static void main(String[] args) { PriorityQueue<Integer> pq = new PriorityQueue<>(); pq.offer(30); pq.offer(10); pq.offer(50); pq.offer(20); System.out.println(pq); while(!pq.isEmpty()) { System.out.println(pq.poll()); } } } Output 10 20 30 50 Elements are removed in priority order (ascending) PriorityQueue is used in: ✔ Task priority scheduling ✔ Load balancing ✔ Path finding algorithms ✔ CPU scheduling 🧠 Key Learning Queue → FIFO data processing Deque → Flexible queue with operations from both ends PriorityQueue → Processes elements based on priority Understanding these structures helps build efficient backend processing systems. #Java #BackendDeveloper #JavaCollections #Queue #Deque #PriorityQueue #SpringBoot #LearningInPublic #SoftwareEngineering

🚀 Day 31 | Core Java Learning Journey 📌 Topic: HashMap & Map Implementations (Internal Working + Concepts) Today, I deep-dived into how HashMap actually works internally along with LinkedHashMap, TreeMap, and Hashtable. This helped me understand not just usage, but the logic behind performance. 🔹 What is HashMap? ✔ HashMap is a class that implements Map interface ✔ Stores data in key-value pairs ✔ Allows one null key and multiple null values ✔ Not synchronized (not thread-safe) 🔹 Internal Working of HashMap ✔ Default initial capacity = 16 (bucket size) ✔ Data is stored in buckets (array of nodes) ✔ Each key’s hashCode() is used to find bucket index ✔ Formula: index = hash(key) & (n - 1) ✔ If two keys have same bucket index → Collision occurs 👉 Collision Handling: • Uses Linked List (before Java 8) • Uses Linked List + Balanced Tree (after Java 8) • If bucket size > 8 → converts into Red-Black Tree • If reduced → converts back to Linked List ✔ Load Factor = 0.75 (default) ✔ When threshold exceeds → resizing (rehashing) happens 🔹 Important Concepts ✔ Bucket → Each index of internal array ✔ Hashing → Converting key into integer hash ✔ Collision → Multiple keys at same index ✔ Rehashing → Increasing size & redistributing data 🔹 LinkedHashMap ✔ Extends HashMap ✔ Maintains insertion order ✔ Uses doubly linked list internally ✔ Slightly slower than HashMap 🔹 TreeMap ✔ Implements NavigableMap ✔ Stores keys in sorted order (natural/custom comparator) ✔ Uses Red-Black Tree internally ✔ Does NOT allow null key 🔹 Hashtable ✔ Legacy class (introduced before collections framework) ✔ Thread-safe (synchronized) ✔ Does NOT allow null key or value ✔ Slower due to synchronization 🔹 Key Differences ✔ HashMap → Fastest, no ordering ✔ LinkedHashMap → Maintains insertion order ✔ TreeMap → Sorted data ✔ Hashtable → Thread-safe but slower 📌 When to Use What? ✅ Use HashMap → Best performance, general use ✅ Use LinkedHashMap → Order matters ✅ Use TreeMap → Sorted output required ✅ Use Hashtable → Thread-safe (but prefer ConcurrentHashMap in modern Java) 💡 Key Takeaway: Understanding internal working of HashMap (buckets, hashing, collisions, rehashing) helps write optimized and scalable code instead of just using it blindly. Special thanks to Vaibhav Barde Sir for the guidance! #CoreJava #JavaLearning #JavaDeveloper #HashMap #LinkedHashMap #TreeMap #Hashtable #JavaCollections #Programming #LearningJourney

🚀 Day 33 | Core Java Learning Journey 📌 Topic: File Handling in Java Today, I explored File Handling in Java — how applications store and retrieve data from files. This is a very important concept for building real-world applications where data persistence is required. 🔹 What is File Handling? ✔ File Handling is used to store data permanently in files ✔ It allows Java applications to read, write, and modify files ✔ Available through the java.io package 🔹 Why We Use File Handling? ✔ To store data permanently (even after program ends) ✔ To read existing data from files ✔ To build data-driven applications ✔ Used in logging, reports, configs, etc. 🔹 Important Classes in java.io.* ✔ File → Represents file or directory ✔ FileWriter → Writes data to file (character stream) ✔ FileReader → Reads data from file ✔ BufferedWriter → Efficient writing (faster) ✔ BufferedReader → Efficient reading (line by line) ✔ FileInputStream → Reads binary data ✔ FileOutputStream → Writes binary data ✔ InputStreamReader → Converts byte stream → character stream 🔹 Steps to Work with Files ✔ Step 1: Import package • import java.io.*; ✔ Step 2: Create File Object • File file = new File("test.txt"); ✔ Step 3: Write Data • FileWriter fw = new FileWriter(file); • fw.write("Hello Students"); ✔ Step 4: Read Data • FileReader fr = new FileReader(file); ✔ Step 5: Close Resources • Always close streams → fw.close(), fr.close() 🔹 Important Methods ✔ createNewFile() → Creates new file ✔ exists() → Checks file existence ✔ delete() → Deletes file ✔ write() → Writes data ✔ read() → Reads single character ✔ readLine() → Reads line (BufferedReader) ✔ flush() → Clears buffer and forces write ✔ close() → Closes stream 🔹 Key Concepts ✔ Buffered Streams → Faster performance ⚡ ✔ Character Streams → FileReader, FileWriter ✔ Byte Streams → FileInputStream, FileOutputStream ✔ Exception Handling → Must handle IOException ✔ Try-with-resources → Recommended (auto close) ✅ 🔹 Example (Best Practice) ✔ Using try-with-resources: • try (FileWriter fw = new FileWriter("test.txt")) { fw.write("Hello Students"); } 🔹 Store & Fetch Data ✔ Store → Using FileWriter / BufferedWriter ✔ Fetch → Using FileReader / BufferedReader ✔ Supports both text and binary data 📌 When to Use File Handling? ✅ When saving user data locally ✅ When working with logs or reports ✅ When database is not required ✅ When handling configuration files 💡 Key Takeaway: File Handling is essential for data persistence in Java. Understanding streams and proper resource management helps build efficient and reliable applications. Special thanks to Vaibhav Barde Sir for the guidance! #CoreJava #JavaLearning #JavaDeveloper #FileHandling #JavaIO #Programming #LearningJourney

📅 Day 38 & 39 – Java Learning Journey | ArrayList (Java Collections Framework) 🚀 In the past two days, I explored ArrayList, one of the most commonly used classes in the Java Collection Framework. Understanding how it works internally helps write efficient and optimized Java programs. 🔹 What is ArrayList? ArrayList is a dynamic array implementation in Java that can automatically grow or shrink in size. Unlike traditional arrays, we don't need to define the size in advance. 🔹 Default Capacity & Internal Resizing When an ArrayList is created: ArrayList<Integer> list = new ArrayList<>(); • Default capacity = 10 • When the array becomes full, Java increases capacity by 50% Formula used internally: newCapacity = oldCapacity + (oldCapacity / 2); Example growth: 10 → 15 → 22 → 33 → 49 → ... Example: import java.util.ArrayList; public class ArrayListDemo { public static void main(String[] args) { ArrayList<String> fruits = new ArrayList<>(); fruits.add("Apple"); fruits.add("Banana"); fruits.add("Mango"); System.out.println(fruits.get(1)); // Access element } } 🔹 Common Operations in ArrayList ✔ Insertion ArrayList<String> fruits = new ArrayList<>(); fruits.add("Apple"); fruits.add("Banana"); fruits.add("Mango"); System.out.println(fruits); Output: [Apple, Banana, Mango] ✔ Accessing Elements System.out.println(fruits.get(1)); Output: Banana ArrayList allows fast access using index. ✔ Updating Elements fruits.set(1, "Orange"); System.out.println(fruits); Output: [Apple, Orange, Mango] ✔ Deleting Elements fruits.remove("Apple"); or fruits.remove(1); Output: [Orange, Mango] ✔ Size of ArrayList System.out.println(fruits.size()); 🔹 Time Complexity of ArrayList Operation TimeComplexity Add element (end)O(1) (Amortized) Access elementO(1) Update elementO(1) Insert element (middle)O(n) Delete elementO(n) Search elementO(n) 💡 Key Takeaways ✔ Dynamic resizing ✔ Maintains insertion order ✔ Allows duplicate values ✔ Null insertion is Possible ✔ Provides fast access with indexes Learning how these internal mechanisms work helps us choose the right data structure while building real-world applications. 🙏 Special thanks to my mentor Suresh Bishnoi from Kodewala Academy for guiding me step by step in my Java Backend Developer journey. #Java #JavaCollections #ArrayList #BackendDevelopment #100DaysOfCode #LearningInPublic #JavaDeveloper

🚀 Day 26 | Core Java Learning Journey 📌 Topic: Legacy Classes in Java & Iteration Interfaces Today I learned about Legacy Classes in Java and the iteration mechanisms used to traverse elements in collections. These concepts were introduced in early versions of Java and later became compatible with the Java Collections Framework. Understanding them helps in learning how Java collections evolved over time. 🔹 What are Legacy Classes in Java? ✔ Legacy Classes are the classes that were introduced before Java 1.2, when the Java Collections Framework did not exist. ✔ These classes were part of the original Java library. ✔ Later, they were updated to work with the Collections Framework, but modern alternatives are usually preferred today. 📌 Five Important Legacy Classes 1️⃣ Vector ✔ Dynamic array similar to ArrayList ✔ Synchronized (thread-safe) by default ✔ Allows duplicate elements ✔ Maintains insertion order 2️⃣ Stack ✔ Subclass of Vector ✔ Follows LIFO (Last In First Out) principle ✔ Common methods: • push() – add element • pop() – remove top element • peek() – view top element 3️⃣ Hashtable ✔ Stores key–value pairs ✔ Synchronized (thread-safe) ✔ Does not allow null key or null value ✔ Considered the older version of HashMap 4️⃣ Dictionary ✔ Abstract class used for storing key–value pairs ✔ Parent class of Hashtable ✔ Rarely used in modern Java 5️⃣ Properties ✔ Subclass of Hashtable ✔ Stores configuration data as String key–value pairs ✔ Commonly used in .properties files 🔹 Iteration Interfaces in Java To traverse elements in collections, Java provides different iteration mechanisms. 📌 Enumeration ✔ One of the oldest iteration interfaces ✔ Mainly used with legacy classes like Vector and Hashtable ✔ Supports read-only traversal Methods: • hasMoreElements() • nextElement() 📌 Iterator ✔ Introduced with the Java Collections Framework ✔ Used to iterate over most collection classes Methods: • hasNext() • next() • remove() 📌 ListIterator ✔ Advanced version of Iterator used with List implementations ✔ Supports bidirectional traversal Additional Methods: • hasPrevious() • previous() • nextIndex() • previousIndex() • add() • set() 📌 Difference: Enumeration vs Iterator vs ListIterator ✔ Enumeration → Used with legacy classes, forward traversal only, no modification ✔ Iterator → Works with most collections, forward traversal, supports remove() ✔ ListIterator → Used with lists, supports forward & backward traversal, allows modification of elements Learning these concepts improves understanding of how Java collections work internally and how iteration mechanisms evolved in Java 💻⚡ Special thanks to Vaibhav Barde Sir for explaining these concepts clearly. #CoreJava #JavaLearning #LegacyClasses #Iterator #ListIterator #Enumeration #JavaCollections #JavaDeveloper #Programming #LearningJourney

🚀 Java Collections Deep Dive: Mastering the ArrayList ✔️ If you are working with data in Java, the ArrayList is likely your most-used tool. But knowing the methods is only half the battle—you also need to know how to handle them safely! 📦 1. Essential ArrayList Methods ✔️ The ArrayList is a dynamic array that provides a massive range of built-in functionality: 🔸 add(element): Add a single element. 🔸 get(index): Retrieves the element at a specific position. 🔸set(index, element): Replaces the element at a specific index. 🔸 remove(index/object): Deletes a specific element or an element at a certain index. 🔸 contains(element): Checks if a single element exists in the list. 🔸 containsAll(collection): Checks if the list contains a group of elements. 🔸 indexOf(element): Finds the first occurrence of an item. 🔸 lastIndexOf(element): Finds the last occurrence of an item. 🔸 size(): Returns the number of elements. 🔸 addAll(collection): Merges another collection into your list. 🔸 clear(): Wipes the entire list clean. 🔸 isEmpty(): A quick boolean check to see if the list is empty. 🛡️ 2. The Role of Generics <T> ✔️ Before Generics, lists could hold any object, which often led to runtime crashes. ✔️By using Generics, we enforce Type Safety. ✔️ Example: ArrayList<String> ensures that only Strings can be added. The compiler checks this for you, so you don't have to worry about ClassCastException later. ⚠️ 3. The ConcurrentModificationException Trap ➡️ Have you ever tried to remove an element while looping through a list using a for-each loop? ❌ CRASH! You’ll get a ConcurrentModificationException. This happens because Java doesn't allow the list's structure to change while it is being traversed by a standard loop. 🔄 4. The Solution: Using an Iterator ✔️ To overcome the crash above, we use an Iterator. It is an object that allows us to traverse the list and modify it safely. 🔹 hasNext(): Checks if there is a next element. 🔹 next(): Returns the next element. 🔹remove(): Safely removes the current element from the list. 💻 The "Interview Special" ➡️ import java.util.*; public class ArrayListMastery { public static void main(String[] args) { ArrayList<String> skills = new ArrayList<>(); skills.add("Java"); skills.add("Spring Boot"); skills.add("Microservices"); skills.add("Java"); System.out.println("Get Index 1: " + skills.get(1)); System.out.println("Contains Java? " + skills.contains("Java")); System.out.println("Last Index: " + skills.lastIndexOf("Java")); //The Interview "Trick": Safe Removal using Iterator // Overcomes ConcurrentModificationException Iterator<String> it = skills.iterator(); while (it.hasNext()) { if (it.next().equals("Java")) { it.remove(); } } System.out.println("Final List: " + skills); } } #Java #CodingInterview #SoftwareEngineering #JavaCollections

Java Programming Complete Notes 🚀 Mastering Java Programming - Detailed Guide 1. Core Java Concepts This section builds a strong foundation in Java by covering: ✔ OOP Principles Encapsulation, Inheritance, Polymorphism, Abstraction. ✓ Collections Framework - List, Set, Map, Queue, their implementations & use cases. ✔ Exception Handling - Try-catch, Finally, Throws, Custom Exceptions. ✔ Multithreading & Concurrency Threads, Synchronization, Executors, Deadlocks. ✔ Java 8 Features - Lambda expressions, Streams API, Functional Interfaces. 2. Advanced Java Topics This section deepens understanding with: ✔JVM Architecture - Heap & Stack memory, Class Loading, Execution Engine. ✔ Garbage Collection - GC Algorithms, Finalization, Memory Optimization. ✔Reflection API - Metadata, Dynamic Object Creation, Annotations. ✔ Serialization & Deserialization Java Object Serialization, Externalizable Interface. 3. Data Structures & Algorithms (DSA) Interviewers test Java proficiency through problem-solving. This guide covers: ✔Arrays & Strings - Sorting, Searching, Sliding Window, Two Pointers. ✔Linked Lists - Reversal, Cycle Detection, Merge, Flattening. ✔ Stacks & Queues - LRU Cache, Min Stack, Circular Queue. ✔ Trees & Graphs - DFS, BFS, Trie, Binary Search Tree, Dijkstra's Algorithm. ✔ Dynamic Programming Fibonacci, Knapsack, Subset Sum, Longest Subsequence. 4. System Design & Architecture For senior-level interviews, system design knowledge is crucial: ✔Scalability & High Availability - Load Balancing, Sharding, Replication. ✔ Microservices Architecture - API Gateway, Service Registry, Circuit Breaker. ✔ Design Patterns Singleton, Factory, Observer, Dependency Injection. ✔ Database Scaling - SQL vs NoSQL, Indexing, Caching Strategies. 5. Java Frameworks & Tools * Interviews often focus on frameworks like: ✔Spring Boot - Dependency Injection, MVC, REST APIs, Security. ✔ Hibernate & JPA-ORM Mapping, Caching, Transactions. ✔ Docker & Kubernetes Containerization for Microservices. ✔ Logging & Monitoring Log4j, Prometheus, Grafana. 6. SQL & Database Management Database-related questions are common, covering: ✔ SQL Queries - Joins, Group By, Indexing, Triggers, Stored Procedures. ✔ Normalization & Denormalization - Database Optimization. ✔ ACID Properties & Transactions - Ensuring data consistency. ✔Redis & Caching Optimizing database performance. 7. Java Interview Questions & Best Practices Includes real-world coding problems and expert tips to crack interviews: ✔ Behavioral & HR Interview - How to answer tricky questions. ✔ Live Coding Tips - Writing clean, optimized Java code. ✔ Mock Interview Scenarios - Simulating real interview environments. ✔ Debugging & Code Optimization Avoiding common mistakes. #Java #JavaInterview #DSA #SpringBoot #Coding #SystemDesign #OOP #InterviewPrep #Backend

🚀 Day 23 | Core Java Learning Journey 📌 Topic: Collection Framework in Java Today I learned about the Collection Framework, one of the most important parts of Java used to store and manage groups of objects efficiently. 🔹 What is a Collection? ✔ A Collection is a framework that provides architecture to store and manipulate a group of objects. ✔ It allows developers to store, retrieve, and manage data dynamically. ✔ Collections can grow or shrink in size automatically unlike arrays. (Wikipedia) 🔹 Important Characteristics of Collections ✔ Collections store objects (non-primitive types) ✔ If primitive data is needed, use wrapper classes like Integer, Double, etc. ✔ Collection size is dynamic (not fixed) ✔ It helps manage large amounts of data efficiently 🔹 Java Collection Framework ✔ The Collection Framework is a unified architecture that provides interfaces, classes, and algorithms to work with groups of objects. (Wikipedia) ✔ It provides ready-to-use data structures like List, Set, Queue, and Map. 🔹 Main Interfaces in Collection Framework 1️⃣ List ✔ Ordered collection ✔ Allows duplicate elements ✔ Example: ArrayList, LinkedList, Vector 2️⃣ Set ✔ Does not allow duplicate elements ✔ Unordered collection ✔ Example: HashSet, LinkedHashSet, TreeSet 3️⃣ Queue ✔ Follows FIFO (First In First Out) principle ✔ Example: PriorityQueue, ArrayDeque 4️⃣ Map ✔ Stores data in key-value pairs ✔ Keys are unique ✔ Example: HashMap, LinkedHashMap, TreeMap ⚠ Note: Map is part of the Collection Framework but it does not extend the Collection interface. 🔹 Packages Used in Collection Framework Most collection classes and interfaces are available in: ✔ import java.util.*; This package includes important interfaces like List, Set, Map, Queue and classes like ArrayList, HashMap, HashSet, LinkedList. (JavaTechOnline) 🔹 Difference Between Collection and Collections ✔ Collection • It is an interface • Root interface of the collection hierarchy • Represents a group of objects ✔ Collections • It is a utility class • Contains static methods for operations like sorting, searching, and synchronization Example methods: Collections.sort() Collections.reverse() Collections.shuffle() 📌 Key Takeaways ✔ Collection Framework helps manage groups of objects efficiently ✔ Collection stores only objects (non-primitive types) ✔ Size of collections is dynamic ✔ Main interfaces: List, Set, Queue, Map ✔ Collection is an interface while Collections is a utility class Understanding the Collection Framework is essential for building efficient and scalable Java applications 💻⚡ Special thanks to Vaibhav Barde Sir. #CoreJava #JavaLearning #JavaCollections #CollectionFramework #JavaDeveloper #Programming #LearningJourney