一、线程状态
public class Thread implements Runnable {
/**
A thread state. A thread can be in one of the following states:
NEW A thread that has not yet started is in this state.
RUNNABLE A thread executing in the Java virtual machine is in this state.
BLOCKED A thread that is blocked waiting for a monitor lock is in this state.
WAITING A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
TIMED_WAITING A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
TERMINATED A thread that has exited is in this state.
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.
*/
//java 线程状态
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;
}
}NEW
线程处于新建状态，还未开启，还未调用start()
RUNNABLE
线程在虚拟机（JVM）上处于执行状态，但是它可能需要等待系统资源，比如处理器。即可能在处理器上并未真正执行，包括操作系统线程状态中的Running 和 Ready
BLOCKED
线程处于阻塞状态，由于synchronized或者wait引起等待获取对象锁
WAITING
线程处于无限等待状态，由于调用了wait无限等待、join无限等待、LockSupport.park无限等待，等待其他线程调用特定的方法，比如notify、notifyAll或者其他线程结束(join引起时)
TIMED_WAITING
线程处于有限等待状态，由于调用了sleep、wait有限等待、join有限等待、LockSupport.parkNanos有限等待、LockSupport.parkUntil有限等待，等待其他线程调用特定的方法或者其他线程结束或者超时
TERMINATED
线程终结状态，线程异常退出或者正常执行结束
二、状态图
这个状态图不准确，
* LockSupport#park，在unpark、超时、interrupt之后都会进入RUNNABLE，即不会进入BLOCKED状态
* sleep超时之后，也是进入RUNNABLE
* wait、join会释放锁，所以需要重新获取锁
上述图中的方法分别属于：
Object(需要加锁、解锁)
wait、notify、notifyAll
Thread
start、sleep、join、interrupt
LockSupport
pack、parkNanos、parkUntil
关键字synchronized
三、特别注意
当其他线程调用notify或者notifyAll时，当前处于WAITING或者TIMED_WAITING的线程将会转为BLOCKED状态
yield()方法时让出当前cpu，线程依旧处于RUNNABLE
四、notify和notifyAll异同
下面等待状态默认包括有限、无限等待
同：
都是用于通知其他处于等待状态的线程
异：
notify选择一个等待线程进行通知，同时也只有被选中的等待线程退出等待（wait）状态，进入阻塞状态，等待获取对象锁。当该被唤醒且获取了对象锁的线程运行结束后，即使对象锁是空闲状态，其他等待线程也无法获取锁，因为还未退出等待（wait）状态。
notifyAll通知所有等待该对象锁的线程，让他们全部退出等待（wait）状态，进入阻塞状态然后他们会竞争对象锁，以后即使没有notify或者notifyAll，也会竞争锁。