《线程的实现方式》

线程的实现方式有四种：

第一种是继承Thread类，第二种是实现Runnable接口；第三种是实现Callable接口；最后是通过线程池创建线程。

1.继承Thread类

        写一个类继承Thread类，重写run()方法，然后调用start()方法启动线程。

        

class SubThread extends Thread{
	public SubThread(String name) {
		super(name);
	}
	@Override
	public void run() {
		for(char c='A';c<='Z';c++) {
			System.out.println(this.getName()+c);
		}
		
	}
}

public class Demo01 {	
	public static void main(String[] args) {
		SubThread t1 = new SubThread("线程甲");
		SubThread t2 = new SubThread("线程乙");
		SubThread t3 = new SubThread("线程丙");
		t1.start();
		t2.start();
		t3.start();
	}
}

2.实现Runnable接口

        写 一个类实现Runnable接口，重写run()方法；用Runnable接口的实现类的对象作为参数去实例化一个Thread对象，调用start()方法启动线程。

abstract class A{
	public abstract void p();
}

class B extends A implements Runnable{
	@Override
	public void p() {
		System.out.println(Thread.currentThread().getName()+"执行");
	}

	@Override
	public void run() {
		p();
	}
}

public class Demo02 {
	public static void main(String[] args) {
		//每个Runnable接口的实现类，封装了线程的执行逻辑
		B b = new B();
		Thread t1 = new Thread(b,"线程1");
		Thread t2 = new Thread(b,"线程2");
		Thread t3 = new Thread(b,"线程3");
		t1.start();
		t2.start();
		t3.start();
	}
}

实现Runnable接口避免了单继承的局限性，代码可以被多个线程共享。 

3. 实现Callable接口

实现Callable接口，重写call()方法实现一个线程。

public class Demo03 {
	
	public static void main(String[] args) throws InterruptedException, ExecutionException {
		//Callable接口实现类，不同数据范围的计算任务
		SubThread1 subThread1 = new SubThread1(0, 200);
		SubThread1 subThread2 = new SubThread1(201, 500);
		SubThread1 subThread3 = new SubThread1(501, 1000);
		
		//Callable --> FutureTask(Runnable接口的实现类)
		FutureTask task1 = new FutureTask<>(subThread1);
		FutureTask task2 = new FutureTask<>(subThread2);
		FutureTask task3 = new FutureTask<>(subThread3);
		
		Thread t1 = new Thread(task1,"线程1");
		Thread t2 = new Thread(task2,"线程2");
		Thread t3 = new Thread(task3,"线程3");
		//线程启动，
		//tack1.run() --> callable.call()--> 结果-->outcome
		t1.start();
		t2.start();
		t3.start();
		
		//线程执行的返回值
		System.out.println(task1.get());
		System.out.println(task2.get());
		System.out.println(task3.get());
	}
}

class SubThread1 implements Callable{
	
	int begin,end;
	public SubThread1(int begin,int end) {
		this.begin = begin;
		this.end   = end; 
	}
	@Override
	public Integer call() throws Exception {
		int sum = 0;
		for(int i=begin;i<=end;i++) {
			sum+=i;
		}
		return sum;
	}
	
}

使用Callable可以在线程任务结束后，会提供一个返回值。在调用了FutureTask的get()方法获取结果时，当前线程就会阻塞，直至call()方法结束返回结果。 

4.通过线程池创建线程 

        线程池可以自动创建也可以手动创建，自动创建体现在Executors工具类中，常见的可以创建

FixedThreadPool：线程数固定的线程池，使用Executors.newFixedThreadPool()创建；
CachedThreadPool：线程数根据任务动态调整的线程池，使用Executors.newCachedThreadPool()创建；
SingleThreadExecutor：仅提供一个单线程的线程池，使用Executors.newSingleThreadExecutor()创建；
ScheduledThreadPool：能实现定时、周期性任务的线程池，使用Executors.newScheduledThreadPool()创建；

public class Demo01 {

	public static void main(String[] args) throws InterruptedException, ExecutionException {
		ExecutorService executorService = Executors.newFixedThreadPool(4);
		
		List> futureList = new ArrayList<>();
		for (int i = 0; i <= 900000; i+=100000) {
			Future f = executorService.submit(new Leijia(i, i+100000));
			futureList.add(f);
		}
		
		
		int result = 0;
		for (int i = 0; i < futureList.size(); i++) {
			
			result += futureList.get(i).get();
		}
		executorService.shutdown();
		while(!executorService.awaitTermination(1, TimeUnit.SECONDS)) {
			System.out.println("还没有关闭");
		}
		
		System.out.println(result);
	}
}

class Leijia implements Callable{

	private int begin,end;
	public Leijia(int begin,int end) {
		this.begin = begin;
		this.end = end;
	}
	@Override
	public Integer call() throws Exception {
		
		int result = 0;
		for (int i = begin; i <= end; i++) {
			result += i;
		}
		System.out.println(Thread.currentThread().getName()+"正在执行"+begin+"到"+end+"的累加");
		return result;
	}
	
}

线程池中的线程自从线程池创建就会处于运行状态。线程任务的执行从提交线程任务开始。submit()方法可以接收Runnable跟Callable接口的实现类对象。excute()方法只能接收Runnable接口的实现类对象。