Java Core Concepts Learning Project

📌 Overview

This project serves as a structured learning resource for core Java concepts. Each package represents a different Java topic, and within each package, there is a class with a main method that can be uncommented and executed to see the concept in action.

The goal of this project is to build deep conceptual understanding of Java fundamentals through practical examples.

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🚀 How to Use

1. Explore Packages – Each package covers a different core Java topic.
2. Run Examples – Execute the main method inside each class.
3. Observe Output Carefully – Focus on why the output occurs.
4. Read Comments – Each class explains the concept in detail.
5. Experiment – Modify code and observe behavior changes.

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📚 Concepts Covered

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1️⃣ Comparable & Comparator (com.java.comparable_comparator)

• Comparable – Defines natural ordering of objects
• Comparator – Defines custom sorting logic
• Sorting objects using both approaches

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2️⃣ Multithreading (com.java.multithreading)

• Understanding Thread vs Runnable
• Creating threads using:
  • Extending Thread
  • Implementing Runnable
• Inter-thread communication using:
  • wait()
  • notify()
• Example:
  • Printing Even & Odd Numbers using two threads in sequence

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3️⃣ Polymorphism & Inheritance (com.java.inheritance)

This module demonstrates core OOP concepts in Java:

🔹 Concepts Covered:

• Method Overriding (Runtime Polymorphism)
• Method Overloading (Compile-time Polymorphism)
• Variable Hiding vs Method Overriding
• Static Method Hiding
• Upcasting & Downcasting
• Runtime Method Dispatch
• ClassCastException (Unsafe Casting)

🔹 Key Learnings:

• Fields are resolved at compile-time
• Methods are resolved at runtime (dynamic binding)
• Static methods are resolved based on reference type
• Overloading is decided at compile-time
• Overriding is decided at runtime

🔹 Example Highlights:

• A obj = new B() → demonstrates runtime polymorphism
• obj.x vs obj.show() → variable vs method behavior
• Safe vs unsafe casting
• Parent calling overridden methods

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4️⃣ String Immutability (string_immutability)

🔹 Concepts Covered:

• String immutability in Java
• Difference between:
  • Heap objects (new String())
  • String Constant Pool (SCP)
• Behavior of:
  • toUpperCase()
  • toLowerCase()
  • toString()

🔹 Key Learnings:

• Strings are immutable
• Operations create new objects only if content changes
• JVM optimizes memory by reusing objects when possible

🔹 Example Highlights:

• Reference comparison (==) behavior
• Same object reuse vs new object creation

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🧠 Project Philosophy

This project is designed to:

• Build strong fundamentals
• Encourage experimentation over memorization
• Develop interview-level clarity
• Strengthen problem-solving mindset

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🔥 Upcoming Concepts

• Exception Handling
• Collections Framework (Deep Dive)
• Generics
• Java Memory Model
• Advanced Multithreading (ExecutorService, Locks, etc.)

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🚀 Contribution / Expansion

Feel free to:

• Add more examples
• Improve explanations
• Extend into advanced topics

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💡 Final Note

Don’t just run the code — understand why it behaves that way.
That’s what makes you a strong developer.

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