Great question! Let’s break down how multithreading works in Java, why it’s important, and how you can use it.

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☕️ What is Multithreading?

✅ Multithreading is the ability to run multiple parts (threads) of a program concurrently.
✅ Each thread is a separate path of execution within a program.
✅ Threads share the same memory space (heap), but each thread gets its own stack.

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🚀 Why Multithreading?

✅ Better performance — You can utilize multi-core CPUs more efficiently.
✅ Responsive programs — For example, in a GUI app, you can run background tasks (like downloading a file) without freezing the UI.
✅ Parallel processing — Break large tasks into smaller independent pieces and run them in parallel (e.g., in web servers handling many requests).

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🧵 How to Create Threads in Java

✅ Option 1: Extend Thread class

class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("Thread running...");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread thread = new MyThread();
        thread.start();  // starts a new thread
    }
}

✅ Option 2: Implement Runnable interface (recommended)

class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Thread running...");
    }
}

public class Main {
    public static void main(String[] args) {
        Thread thread = new Thread(new MyRunnable());
        thread.start();
    }
}

✅ Option 3: Use Lambda (Java 8+)

public class Main {
    public static void main(String[] args) {
        Thread thread = new Thread(() -> System.out.println("Thread running..."));
        thread.start();
    }
}

🔄 Thread Lifecycle

State	Description
NEW	Created but not started (new Thread()).
RUNNABLE	Running or ready to run (after start()).
BLOCKED	Waiting to acquire a lock.
WAITING	Waiting indefinitely for another thread’s signal.
TIMED_WAITING	Waiting for a specific time (e.g., sleep(1000)).
TERMINATED	Completed or stopped by exception.

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⚙️ Synchronization (Thread Safety)

Since threads share memory, data races can occur if multiple threads access/modify the same object simultaneously. To avoid this, Java provides:

✅ synchronized keyword (lock object/monitor)

synchronized void criticalSection() {
    // only one thread at a time can enter here
}

✅ Locks (ReentrantLock) ✅ Atomic variables (AtomicInteger) ✅ Concurrent collections (ConcurrentHashMap)

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🏗️ Executor Framework (Better Thread Management)

Instead of creating and managing threads manually, use:

ExecutorService executor = Executors.newFixedThreadPool(5);
executor.submit(() -> System.out.println("Task running"));
executor.shutdown();

✅ Better performance (thread pooling)
✅ Automatic thread reuse
✅ Handles task queuing