NEW 初始
构造一个线程实例后、启动前，线程处于该状态
RUNNABLE 运行
该状态包含了经典线程模型的两种状态：就绪 (Ready)、运行(Running)：
就绪状态表示有资格运行，但如果一直没拿到时间片，就一直是就绪状态
- 初始状态的线程，start()方法被调用后，就进入 RUNNABLE 状态，表示就绪(Ready)；并开始等待 CPU 时间片；
- 等待或阻塞状态结束，如 sleep()结束、或其他线程 join()结束、拿到锁，也会进入就绪状态
- 线程时间片用完，线程的 yield()方法会被调用，线程随即进入就绪状态
当线程调度选中该线程、并分配了 CPU 时间片后，该线程尽管处于 Runnable 状态，但实际上是运行(Running)；
- 这是线程进入运行状态的唯一方式
BLOCKED 阻塞
通常与锁有关系，表示线程正在获取有锁控制的资源，比如进入 synchronized 代码块，获取 ReentryLock 等
WAITING
进入该状态的线程，等待被显式唤醒（其他线程发出通知或中断，如 notify/notifyAll, 或者另外的线程终止如join 的情况），否则处于无限期等待
TIMED_WAITING 超时等待
该状态不同于 WAITING，它可以在指定的时间后自动唤醒；
- 处于这种状态的线程不会被分配 CPU 执行时间；
-
Thread.sleep()执行后，线程就会进入该状态
TERMINATED 终止
表示该线程已经执行完毕；
- 线程 Run 方法体结束、或主线程（守护线程）的
main()方法完成时，线程就认为终止了； - 线程对象可能还存活，但不再是单独执行的线程
- 终止的线程不允许再调用
Thread.start()方法
引用 Thread 源码
public enum State {
/**
* Thread state for a thread which has not yet started.
*/
NEW,
/**
* Thread state for a runnable thread. A thread in the runnable
* state is executing in the Java virtual machine but it may
* be waiting for other resources from the operating system
* such as processor.
*/
RUNNABLE,
/**
* Thread state for a thread blocked waiting for a monitor lock.
* A thread in the blocked state is waiting for a monitor lock
* to enter a synchronized block/method or
* reenter a synchronized block/method after calling
* {@link Object#wait() Object.wait}.
*/
BLOCKED,
/**
* Thread state for a waiting thread.
* A thread is in the waiting state due to calling one of the
* following methods:
* <ul>
* <li>{@link Object#wait() Object.wait} with no timeout</li>
* <li>{@link #join() Thread.join} with no timeout</li>
* <li>{@link LockSupport#park() LockSupport.park}</li>
* </ul>
*
* <p>A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called {@code Object.wait()}
* on an object is waiting for another thread to call
* {@code Object.notify()} or {@code Object.notifyAll()} on
* that object. A thread that has called {@code Thread.join()}
* is waiting for a specified thread to terminate.
*/
WAITING,
/**
* Thread state for a waiting thread with a specified waiting time.
* A thread is in the timed waiting state due to calling one of
* the following methods with a specified positive waiting time:
* <ul>
* <li>{@link #sleep Thread.sleep}</li>
* <li>{@link Object#wait(long) Object.wait} with timeout</li>
* <li>{@link #join(long) Thread.join} with timeout</li>
* <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
* <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
* </ul>
*/
TIMED_WAITING,
/**
* Thread state for a terminated thread.
* The thread has completed execution.
*/
TERMINATED;
}