Java线程
我为什么要写这篇文章？主要有一下几点：
- 加深自己对Java线程的理解
- 勘误网上有些错误的知识和认知
- 通过写文章，来交流思想
网上关于Java线程的文章数不胜数，实在太多了，我又怎么写一篇让其他人一看就懂，一看就会，一看就忘不掉的文章呢？
- 用假如我是面试官的场景和面试官的角度去深入分析Java线程相关的知识，下面就开始吧！
这个时候，大部分同学都应该能回答上来，但是，答案有可能不一样，因为百度上面有五种、六种的很多说法，你说哪个是对的？如下图：Java中Thread的状态（State）
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这个时候你慌不慌，百度是不可靠的，那么可靠的答案在哪里？在源码里面
/**
* A thread state.A thread can be in one of the following states:
*
* - {@link #NEW}
*A thread that has not yet started is in this state.
*
* - {@link #RUNNABLE}
*A thread executing in the Java virtual machine is in this state.
*
* - {@link #BLOCKED}
*A thread that is blocked waiting for a monitor lock
*is in this state.
*
* - {@link #WAITING}
*A thread that is waiting indefinitely for another thread to
*perform a particular action is in this state.
*
* - {@link #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.
*
* - {@link #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.
*
* @since1.5
* @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:
*
*- {@link Object#wait() Object.wait} with no timeout
*- {@link #join() Thread.join} with no timeout
*- {@link LockSupport#park() LockSupport.park}
*
*
* A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called Object.wait()
* on an object is waiting for another thread to call
* Object.notify() or Object.notifyAll() on
* that object. A thread that has called 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:
*
*- {@link #sleep Thread.sleep}
*- {@link Object#wait(long) Object.wait} with timeout
*- {@link #join(long) Thread.join} with timeout
*- {@link LockSupport#parkNanos LockSupport.parkNanos}
*- {@link LockSupport#parkUntil LockSupport.parkUntil}
*
*/
TIMED_WAITING,/**
* Thread state for a terminated thread.
* The thread has completed execution.
*/
TERMINATED;
}
java中线程的状态有6中，其中包括：NEW（新建），RUNNABLE（运行，可能抢到了CPU，也可能没有抢到），BLOCKED（阻塞），WAITING（等待），TIMED_WAITING（加上时间的等待），TERMINATED（销毁）。NO2.线程的状态流转，你能讲一下？
我相信很多人都能回答上来，但是，都不是实际的使用经验，而是背下来的。那么，我们来深入的实践一下！线程状态流转图
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sleep时候，线程是什么状态？
线程在sleep的时候，是TIMED_WAITING状态或者RUNNABLE状态，决定因素是sleep的时间是0，或者大于0的值：Join的时候，线程是什么状态？
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线程在join的时候，是TIMED_WAITING或者WAITING，决定因素是有没有加上时间。Wait时候是什么状态？
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线程在wait的时候，是TIMED_WAITING或者WAITING，决定因素是有没有加上时间。抢不到锁的时候，是什么状态？
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抢不到锁的时候是BLOCKED状态NO3.线程通信
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控制两个线程交换打印（手写）
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把一副扑克分给4个人（手写）
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NO4.线程安全与可见性
【关于Java线程，你必须掌握的知识点】安全和可见性，就不展开写了。关注synchronized、volatile，这里面就设计到JMM的知识了。
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