Java创建线程的4种方式

继承Thread类，重写run方法

Thread类实现了Runnable接口（只有一个没有返回值的run方法）。

public class ThreadDemo extends Thread {
    public ThreadDemo(String name) {
        super(name);
    }

    @Override
    public void run() {
        System.out.println(getName());
    }

    public static void main(String[] args) {
        ThreadDemo thread1 = new ThreadDemo("thread1");
        ThreadDemo thread2 = new ThreadDemo("thread2");
        thread1.start();
        thread2.start();
    }
}

运行结果

thread2
thread1

实现Runnable接口，重写run方法

相比于继承Thread类，通过同一个实现了Runnable接口的对象来构造Thread对象，可以避免单继承的缺陷和实现资源共享。

public class ThreadDemo implements Runnable {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }

    public static void main(String[] args) {
        ThreadDemo thread = new ThreadDemo();
        Thread thread1 = new Thread(thread, "thread1");
        Thread thread2 = new Thread(thread, "thread2");
        thread1.start();
        thread2.start();
    }
}

运行结果

thread1
thread2

实现Callable接口，重写call方法

Callable接口只有一个call方法。相比于run方法，有返回值，且返回值支持泛型，可以抛出异常，借助FutureTask类来获取返回结果。
针对Runnable或者Callable任务，Future接口支持判断任务是否完成、中断任务、获取任务执行结果（get方法阻塞直到任务返回结果），唯一实现类是FutureTask。
FutureTask实现了RunnableFuture接口，RunnableFuture接口继承了Runnable和Future接口。

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class ThreadDemo implements Callable<String> {
    @Override
    public String call() throws Exception {
        return "thread";
    }

    public static void main(String[] args) {
        ThreadDemo threadDemo = new ThreadDemo();
        FutureTask<String> futureTask = new FutureTask<>(threadDemo);
        new Thread(futureTask).start();

        String s = "";
        try {
            s = futureTask.get();
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }

        System.out.println(s);
    }
}

运行结果

thread

使用ThreadPoolExecutor来创建线程池

ThreadPoolExecutor实现了Executor接口。
使用线程池，降低资源消耗，提高响应速度，提高线程的可管理性。

基于初始容量为10的有界任务队列来创建核心容量为10、最大容量为20、线程存活时间为1分钟的线程池

import java.util.concurrent.*;

public class ThreadDemo implements Runnable {
    public static void main(String[] args) {
        BlockingQueue<Runnable> blockingQueue = new ArrayBlockingQueue<>(10);
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                10, 20, 1, TimeUnit.MINUTES, blockingQueue, Executors.defaultThreadFactory());

        for (int i = 0; i < 10; i++) {
            threadPoolExecutor.submit(new ThreadDemo());
        }
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

运行结果

pool-1-thread-2
pool-1-thread-6
pool-1-thread-3
pool-1-thread-9
pool-1-thread-1
pool-1-thread-4
pool-1-thread-7
pool-1-thread-5
pool-1-thread-8
pool-1-thread-10