#41 | Explain the Thread lifecycle and its states. | Java Interview

In this video, we explain the Thread Lifecycle in Java and its states — a must-know topic for Core Java and Multithreading interviews. Instead of memorizing diagrams, you’ll understand how threads actually move between states, why certain states exist, and what interviewers expect you to explain clearly.

A Java thread doesn’t just run and stop. It goes through well-defined states managed by the JVM, from creation to termination.

👨‍💻 What you’ll learn:

States of a Thread (Java Thread.State)

• NEW – Thread is created but not started
• RUNNABLE – Thread is ready to run and waiting for CPU time
• BLOCKED – Waiting to acquire a monitor lock
• WAITING – Waiting indefinitely for another thread’s action
• TIMED_WAITING – Waiting for a specified time
• TERMINATED – Execution finished, thread is dead

You’ll understand what each state means, when a thread enters it, and how it exits that state.

Lifecycle Methods (Conceptually)

• start() – Moves thread from NEW to RUNNABLE
• run() – Contains execution logic
• sleep() – Causes TIMED_WAITING
• wait() / join() – Causes WAITING or TIMED_WAITING
• Thread completion – Leads to TERMINATED

Thread State Transitions Explained

• NEW → RUNNABLE (start called)
• RUNNABLE → BLOCKED (waiting for lock)
• RUNNABLE → WAITING / TIMED_WAITING (wait, sleep, join)
• WAITING / TIMED_WAITING → RUNNABLE (notified or timeout)
• RUNNABLE → TERMINATED (execution finishes)

We also clarify a very common confusion:
Why you don’t see a separate RUNNING state in Java — because the JVM combines “ready” and “running” into RUNNABLE.

Code Demonstration (Conceptual Understanding)

• Observe thread states using getState()
• Watch transitions after start(), sleep(), and join()
• Understand how JVM reports thread state at runtime

🎯 What interviewers expect:
• You know all six thread states
• You can explain state transitions logically
• You understand BLOCKED vs WAITING vs TIMED_WAITING
• You know why RUNNING is not a separate state
• You can explain lifecycle without memorizing diagrams

🧠 How you should answer in interviews:
A Java thread goes through states like NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING, and TERMINATED. The JVM manages these transitions based on thread execution, synchronization, and waiting conditions. Threads do not jump randomly — every transition has a clear reason.

This video is perfect for Core Java interviews, multithreading fundamentals, backend preparation, and JVM concepts.

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