线程的生命周期：
1. 新建（New）: 调用new方法，新建一个线程时，线程处于生命周期中的New。此时主要是为线程分配内存，初始化其成员变量。
2. 就绪（Runnable）:调用start方法，启动一个线程。此时JVM完成了栈和程序计数器的创建，等待该线程的调度和运行。
3. 运行（Running）:当处于Runnable的线程，被分配到CPU时间片后，线程开始执行run方法，此时处于运行状态。运行状态主要是执行run方法中的代码逻辑。
4. 阻塞（Blocked）:运行中的线程，主动或者被动的放弃CPU的使用权暂停运行。线程调用Object.wait()方法（等待阻塞），没有竞争到锁而阻塞（同步阻塞），线程调用Thread.sleep()，Thread
.join()方法（其他阻塞）
5. 死亡（Dead）:线程运行结束，或者因为异常退出。
线程的6种状态：
1. NEW:线程被创建还没有运行（start）时的状态。
2. RUNNABLE:线程在JAVA虚拟机运行时的状态。
3. BLOCKED：线程被阻塞，因为运行synchronized的同步方法时，没有竞争到锁而被阻塞时的状态。
4. WAITING：由于调用了Object.wait(),Thread.join()，LockSupport.park()等f非超时方法，导致线程处于等待状态，需要别的线程唤醒。
5. TIMED_WAITING：由于调用了Thread.sleep，Object.wait(long),Thread.join(long),LockSupport.parkNanos(),LockSupport.parkUntil()等方法时线程处于的状态。它和WAITING状态不同之处在于。它设置了超时等待的时间，而WAITING状态没有。
6. TERMINATED：线程已经退出时的状态。
/**
* A thread state. A thread can be in one of the following states:
* <ul>
* <li>{@link #NEW}<br>
* A thread that has not yet started is in this state.
* </li>
* <li>{@link #RUNNABLE}<br>
* A thread executing in the Java virtual machine is in this state.
* </li>
* <li>{@link #BLOCKED}<br>
* A thread that is blocked waiting for a monitor lock
* is in this state.
* </li>
* <li>{@link #WAITING}<br>
* A thread that is waiting indefinitely for another thread to
* perform a particular action is in this state.
* </li>
* <li>{@link #TIMED_WAITING}<br>
* A thread that is waiting for another thread to perform an action
* for up to a specified waiting time is in this state.
* </li>
* <li>{@link #TERMINATED}<br>
* A thread that has exited is in this state.
* </li>
* </ul>
*
* <p>
* A thread can be in only one state at a given point in time.
* These states are virtual machine states which do not reflect
* any operating system thread states.
*
* @since 1.5
* @see #getState
*/
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 <tt>Object.wait()</tt>
* on an object is waiting for another thread to call
* <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
* that object. A thread that has called <tt>Thread.join()</tt>
* 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;
}
