NEW状态表示刚刚创建的线程,这种线程还没开始执行。等到线程的start()方法调用时。才表示线程开始执行。当现场执行时,处于RUNNABLE状态,表示线程所需的一切资源都已经准备好了。如果线程在执行过程中遇到了synchronized同步块,就会进入BLOCKED阻塞状态,这时线程就会暂停执行,直到获得请求的锁。WAITING和TIMED_WAITING都表示等待状态,它们的区别是WAITING会进入一个无时间限制的等待,TIMED_WAITING会进行一个有时限的等待。那等待的线程究竟在等什么呢?一般来说,WAITING的线程正是在等待一些特殊的事件。比如,通过wait()方法等待的线程在等待notify()方法,而通过join()方法等待的线程则会等待目标线程的终止。一旦等到了期望的事件,线程就会再次执行,进入RUNNABLE状态。当线程执行完毕后,则进入TERMINATED状态,标识结束。
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.
* <p>
* 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;
}
注意:从NEW状态发出后,线程不能再回到NEW状态,同理,处于TERMINATED的线程也不能再回到RUNNABLE状态。