线程的生命周期
1.线程状态介绍
NEW
Thread state for a thread which has not yet started.
新建：已经创建线程，但还没有启动
RUNNABLE
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.
可运行：包括就绪状态和运行状态
BLOCKED
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 Object.wait.
阻塞：等待获取锁
WAITING
A thread in the waiting state is waiting for another thread to perform a particular action.
等待：调用以下方法时处于等待状态
Thread state for a waiting thread. A thread is in the waiting state due to calling one of the following methods:
- Object.wait with no timeout
- Thread.join with no timeout
- LockSupport.park
TIMED_WAITING
Thread state for a waiting thread with a specified waiting time.
超时等待：可以指定等待时间
A thread is in the timed waiting state due to calling one of the following methods with a specified positive waiting time:
- Thread.sleep
- Object.wait with timeout
- Thread.join with timeout
- LockSupport.parkNanos
- LockSupport.parkUntil
TERMINATED
Thread state for a terminated thread. The thread has completed execution.
终止：线程执行完毕。