Construct a thread life-cycle diagram showing the major states through which a Java thread can pass. Analyse transitions caused by start(), scheduling

Question

Construct a thread life-cycle diagram showing the major states through which a Java thread can pass. Analyse transitions caused by `start()`, scheduling, waiting and termination.

Accepted Answer

## Java thread life cycle

A Java thread may be `NEW`, `RUNNABLE` (eligible to run, including running), `BLOCKED`, `WAITING`, `TIMED_WAITING`, or `TERMINATED`. The scheduler decides when a runnable thread gets CPU time.

```mermaid
stateDiagram-v2
[*] --> NEW
NEW --> RUNNABLE: start()
RUNNABLE --> BLOCKED: waiting for monitor lock
RUNNABLE --> WAITING: wait() / join()
RUNNABLE --> TIMED_WAITING: sleep(t) / timed wait
BLOCKED --> RUNNABLE: lock acquired
WAITING --> RUNNABLE: notify / joined thread ends
TIMED_WAITING --> RUNNABLE: timeout / signal
RUNNABLE --> TERMINATED: run() completes
TERMINATED --> [*]
```

Calling `start()` schedules a new thread; calling `run()` directly is an ordinary method call. A terminated thread cannot be restarted.

Java thread life cycle

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