Java多线程

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Runnable

interface：它是一个接口
run()：它唯一的方法，一个run需要实现的方法，线程的逻辑写在这里

class RunnableDemo implements Runnable{    @override    public void run(){    //do something...     }}public static void main(String[] args){    Thread t = new Thread(new RunnableDemo());    t.start();}

Thread（单继承方式）

class：首先它是一个类，它implements Runnable，getName()可以获取它的名字，setName()可以设置它的名字
run()：重写Runnable的方法，它也不实现，只是调用Runnable的run()
start()：the JVM calls the run method of thread.
sleep()：params is millis.
yeild()：the current thread is willing to yeild its current use of processor,the scheduler is free.
join()：wait for this thread to die.
currentThread()：return a reference to the currently executing thread object.

class ThreadDemo extends Thread{    @override    public void run(){    //do something    }}public static void main(String[] args){    Thread t = new ThreadDemo();    t.start();}

Synchronized

synchronized(object){}块实现线程互斥
运用Object的wait/notify/notifyAll方法实现线程同步

synchronized(object){    object.wait();    object.notify();    obejct.notifyALl();}

wait()：the current thread to wait until another thread invokes the notify() method or the notifyAll() for this object.
synchronized也可用于修饰方式，一个被synchronized修饰的方法，保证了线程的安全性，这个方法没被执行完或者没有调用wait方法之前，其他线程都被阻塞，直到方法执行完或者调用wait方法。

volatile

保证了线程可以正确地读取其他线程写入的数据
原因：线程内存可见性，JMM，happens-before原则
注意：volatile只适用于更改数据不依赖于数据本身，比如boolean变量，温度变量等。

Daemon

守护线程

thread.setDaemon(true)

在start()之前设置，否则会抛IllegalThreadStateException。
在Daemon线程中产生的新线程也是Daemon的。
不是所有的应用都可以分配给Daemon线程来进行服务，比如读写操作或者计算逻辑。因为如果没有线程让守护线程守护的话，Daemon Thread还没来的及进行操作时，Daemon Thread可能随着JVM退出了。

Callable、Futrue、ExecutorService、CountDownLatch

实现Callable接口类

public class TestCallable implements Callable<Integer>{    private CountDownLatch countDownLatch;    public TestCallable(CountDownLatch countDownLatch){        this.countDownLatch=countDownLatch;    }    @Override    public Integer call() throws Exception {        System.out.println(Thread.currentThread().getName()+"run...");        final long numSleep = 10000;         int r = (int)(Math.random()*10);        System.out.println("start sleep "+Math.floor(numSleep/1000)+" seconds...");        Thread.sleep(numSleep);        System.out.println("wake up!");        countDownLatch.countDown();        System.out.println(Thread.currentThread().getName()+"end!");        return r;    }}

测试方法：

public static void main(String[] args) throws InterruptedException, ExecutionException {        final int numThread = 3;        List<Future<Integer>> futureList = new ArrayList<>();        CountDownLatch countDownLatch = new CountDownLatch(numThread);//      ExecutorService pool = Executors.newCachedThreadPool();        ExecutorService pool = Executors.newFixedThreadPool(numThread);        for(int i=0;i<numThread;i++){            Callable<Integer> c1 =  new TestCallable(countDownLatch);            Thread.currentThread().setName("thread-"+i);            futureList.add(pool.submit(c1));        }        pool.shutdown();        countDownLatch.await();        for (Future<Integer> future : futureList) {            if(future.isDone()){                System.out.println(future.get());            }else{                System.out.println("f is running...");            }        }    }

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