Thread Lifecycle & States

A Java thread goes through multiple states from creation to termination.
These states are defined in the Thread.State enum.

Lifecycle Diagram (Simplified)

NEW → RUNNABLE → RUNNING → (WAITING / BLOCKED / TIMED_WAITING) → TERMINATED

Thread States

State	Description
NEW	Thread is created but not started
RUNNABLE	Thread is ready to run, waiting for CPU
RUNNING	Thread is currently executing its run() method
BLOCKED	Waiting for a lock held by another thread
WAITING	Waiting indefinitely (e.g. wait())
TIMED_WAITING	Waiting with a timeout (e.g. sleep(), join(timeout))
TERMINATED	Thread has completed execution or was stopped

Example

Thread t = new Thread(() -> {
    try {
        Thread.sleep(1000); // TIMED_WAITING
    } catch (InterruptedException e) {}
});
 
System.out.println(t.getState()); // NEW
t.start();
System.out.println(t.getState()); // RUNNABLE → RUNNING

Transition Triggers

Action	State Change
start()	NEW → RUNNABLE
Thread gets CPU	RUNNABLE → RUNNING
sleep(), join(), etc	RUNNING → TIMED_WAITING
wait()	RUNNING → WAITING
Lock contention	RUNNING → BLOCKED
Thread ends	Any → TERMINATED

Tip

Be ready to:

• explain thread states with real examples,
• describe how sleep(), wait(), join() affect state,
• use getState() for debugging multithreaded apps.

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Parent: _Multithreading