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✅ The Thread class in Java just implements the Runnable interface. so…

🧵 The Core Difference

Let’s break it down step by step:

🧠 Core Difference

🔨 1. Extending Thread Class

class MyThread extends Thread {
    public void run() {
        System.out.println("Hello from thread!");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.start(); // Don't call run() directly!
    }
}

✅ Easy to use
❌ Can’t extend another class (Java has single inheritance)

🌱 What Are Green Threads?

Green threads are threads that are scheduled and managed entirely by the JVM (or user-level runtime), not the OS.

That means:

• The JVM simulates threading using only one OS thread (or very few)
• Thread switching is handled inside the JVM, not by the OS
• Good for platforms where OS threads are expensive or unavailable

🧠 Think of green threads as “user-mode” threads.

🧠 What’s the Difference Between a Process and a Thread?

🧩 1. Ordering

Ordering is about the sequence of execution of operations (like reads and writes). It matters because compilers, JVM, and CPUs may reorder instructions to optimize performance.

x = 1;
y = 2;

You’d assume x is set before y, but the JVM might reorder this if it thinks it’s safe to do so — unless there’s a rule (like happens-before) that prevents it.

🧠 What is Cooperative Multitasking?

🧩 Cooperative multitasking means:
Tasks (threads/processes) voluntarily yield control of the CPU so others can run.

🔧 How It Works:

• The OS does not forcibly interrupt a running task.
• It relies on each task to be nice and call yield() or similar.
• If a task never yields, it can monopolize the CPU.

🛠 Used in:

• Very early OSes (Windows 3.1, early MacOS)
• Some embedded systems
• Coroutines / fibers / green threads (e.g., Kotlin coroutines)

❓ Can you adjust ThreadPoolExecutor to run on different cores?

⚠️ Short Answer: Not directly in Java — you cannot manually bind threads to specific cores using ThreadPoolExecutor or Java alone.

But…

✅ Long Answer: You can influence it indirectly and even hack it a bit if you’re determined 😎

✅ Yes, ForkJoinPool is more effective than ThreadPoolExecutor in certain scenarios — but not always.

Let’s dive into when and why ForkJoinPool outperforms ThreadPoolExecutor, and when it might not.