📚 Java Advanced Concepts (Q21–Q30)

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21. 📦 Java Collections Framework

The Java Collections Framework (JCF) is a unified architecture for storing and manipulating groups of objects.

🔑 Core Interfaces:

• List: Ordered collection (e.g., ArrayList, LinkedList)
• Set: No duplicate elements (e.g., HashSet, TreeSet)
• Map: Key-value pairs (e.g., HashMap, TreeMap)

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22. 🔁 ArrayList vs LinkedList

Feature	ArrayList	LinkedList
Backed by	Dynamic array	Doubly-linked list
Access time	Fast (O(1))	Slow (O(n))
Insert/Delete	Slower (shifting required)	Faster (no shifting)
Memory usage	Less overhead	More overhead (node pointers)

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23. 🧠 HashMap Internal Working

• Stores key-value pairs using a hash table.
• Key is hashed → index is calculated → value is stored.
• Collisions are handled using LinkedList or Red-Black Trees (Java 8+).

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24. 🧮 equals() vs hashCode()

Method	Purpose
equals()	Checks logical equality of objects
hashCode()	Returns hash value for use in hash-based collections

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25. 🔄 Comparable vs Comparator

Feature	Comparable	Comparator
Package	java.lang	java.util
Method	compareTo()	compare()
Use case	Natural ordering	Custom ordering
Implementation	Implemented by class	Passed as argument

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26. 🧠 Java Memory Model (JMM)

The Java Memory Model defines how threads interact through memory:

• Ensures visibility and ordering of shared variables.
• Prevents race conditions and inconsistent reads.

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27. 🗑️ Garbage Collection in Java

Garbage Collection (GC) automatically reclaims memory by:

• Identifying unreachable objects.
• Deallocating memory in the heap.
• Using algorithms like Mark-and-Sweep, G1, etc.

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28. 🏷️ Java Annotations

Annotations provide metadata about code.

Common Annotations:

• @Override: Indicates method overrides a superclass method.
• @Deprecated: Marks method as outdated.
• @SuppressWarnings: Suppresses compiler warnings.

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29. 🔀 Lambda Expressions

Lambda expressions provide a concise way to implement functional interfaces.

List<Integer> list = Arrays.asList(1, 2, 3);
list.forEach(n -> System.out.println(n));

Benefits: Less boilerplate Enables functional programming

30. 🌊 Stream API in Java

The Stream API processes collections in a functional style.

Key Operations: filter(): Filters elements

map(): Transforms elements

reduce(): Aggregates elements

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.stream().filter(n -> n.startsWith("A")).forEach(System.out::println);

📌 What’s Next?

👉 Explore detailed answers, code samples, use cases, and illustrations in upcoming parts of this series:

• Part 1: Object-Oriented Basics & Language Features
• Part 2: Interfaces, Modifiers & Packaging
• Part 0: All 50 Questions
• Part 4: Functional APIs, Exceptions & Final Keywords
• Part 5: Advanced Concepts, Concurrency & Modularity