Thread Lifecycle

A thread in Java goes through various states from creation to termination. These stages form the Thread Lifecycle.

🚦 Lifecycle States of a Thread:

1. New

2. Runnable

3. Running

4. Blocked/Waiting

5. Terminated (Dead)

1️⃣ New

• The thread is created but not started yet.

• Happens when you create a thread object using new.

🧾 Example:

Thread t = new Thread(); // NEW state

2️⃣ Runnable

• The thread is ready to run, but it’s waiting for the CPU.

• Happens after calling .start().

🧾 Example:

t.start(); // Now in RUNNABLE state

3️⃣ Running

• The thread is actively executing the run() method.

• It moves from Runnable → Running when the CPU selects it.

🧠 Note:

• You cannot control when it moves to running — the CPU scheduler decides.

4️⃣ Blocked / Waiting / Timed Waiting

A thread moves to waiting states when:

• It’s waiting for another thread or resource.

• It’s paused for a specific time.

🔸 Blocked:

Waiting to acquire a lock held by another thread.

🔸 Waiting:

Waiting indefinitely until notified.

🔸 Timed Waiting:

Waiting for a fixed time (e.g., using sleep() or join(timeout))

🧾 Example:

Thread.sleep(2000);  // Moves to TIMED_WAITING state

5️⃣ Terminated (Dead)

• The thread has finished executing or was forcefully stopped.

• Once dead, it cannot be restarted.

🧾 Example:

public void run() {
    System.out.println("Thread ended.");
}

🧠 Summary Table