線(xiàn)程生命週期包含五個(gè)明確狀態(tài)：1.新建狀態(tài)（New）：線(xiàn)程被創(chuàng)建但尚未啟動(dòng)，不消耗CPU資源；2.可運(yùn)行狀態(tài)（Runnable）：線(xiàn)程已啟動(dòng)並等待或正在執(zhí)行，具體由調(diào)度器決定；3.阻塞/等待狀態(tài)（Blocked/Waiting/Timed Waiting）：線(xiàn)程因鎖、無(wú)限等待或超時(shí)等待而不執(zhí)行，但仍存活；4.終止?fàn)顟B(tài)（Terminated）：線(xiàn)程完成任務(wù)或異常退出後進(jìn)入此狀態(tài)，無(wú)法重啟；5.整個(gè)生命週期中，線(xiàn)程狀態(tài)依次轉(zhuǎn)換，理解這些狀態(tài)有助於避免死鎖和資源競(jìng)爭(zhēng)問(wèn)題。

A thread's lifecycle might sound complicated, but it's actually pretty straightforward once you break it down. In short, a thread goes through several well-defined states from the moment it's created until it's no longer running.

Here's how it typically works:

New – When the thread is born

When you create a new Thread object in Java (or equivalent in other languages), it's in the new state. At this point, the thread exists, but it hasn't started yet. It doesn't consume CPU time here because it hasn't been scheduled to run.

For example:

 Thread myThread = new Thread(() -> System.out.println("Running"));

This thread is in the new state. Nothing runs yet — not even the code inside the run() method.

Key thing to remember:

• You can't restart a thread once it's left this state.
• Only one method can be called here: .start()

Runnable – Ready or actively running

Once you call .start() , the thread moves into the runnable state. This means it's eligible to run — either it's currently executing or waiting for its turn on the CPU.

It depends on the thread scheduler , which decides when each thread gets CPU time. So even if your thread is technically "running", it might just be waiting in line behind others.

Some things that keep a thread in this state:

• The thread is actively doing work
• It's paused briefly by the system to let other threads run
• It's waiting for I/O (but not blocked — more on that later)

Blocked / Waiting / Timed Waiting – Not running, but still alive

These are all variations of non-running states where the thread isn't executing code, but hasn't finished either.

• Blocked : Waiting for a monitor lock (like when entering a synchronized block)
• Waiting : Waiting indefinitely for another thread to do something (eg, wait() , join() )
• Timed Waiting : Same as waiting, but with a timeout (like sleep() , or timed wait() )

In these states, the thread is still considered alive but not consuming CPU cycles.

Terminated – All done

The thread reaches the terminated (or dead ) state when:

• Its run() method finishes normally
• An uncaught exception causes it to crash

Once a thread is dead, it stays dead. You can't restart it. Calling .start() again will throw an exception.

Also, there's no guaranteed way to force-stop a thread externally — which is why we often use flags like isRunning = false to signal it to stop gracefully.

That's basically how a thread moves through its life. Each state has its own role and behavior, and understanding them helps avoid common pitfalls like deadlock, race conditions, or trying to reuse a thread after it's finished.

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