实现线程有哪几种方式？

1、实现Runnable接口，重写run方法，并将该对象传入Thread对象的构造方法中。代码示例如下：

public class RunnableThread implements Runnable {

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

    public static void main(String[] args) {
        RunnableThread runnableThread = new RunnableThread();
        Thread thread = new Thread(runnableThread);
        thread.start();
    }
}

2、继承Thread类，重写run方法。代码示例如下：

public class ExtendsThread extends Thread {

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

    public static void main(String[] args) {
        ExtendsThread extendsThread = new ExtendsThread();
        extendsThread.start();
    }
}

3、线程池中由线程工厂创建线程，本质上是new Thread()创建的。jdk源码如下：

/**
     * The default thread factory
     */
    static class DefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

4、实现Callbale<V>接口，重写call方法。代码示例如下：

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

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        Future<String> future = executorService.submit(new CallableThread());
        String s = future.get();
        System.out.println(s);
    }
}

5、定时器Timer中有一个TimerThread，本质上还是通过继承Thread创建线程的。jdk源码如下：

public class Timer {

    /**
     * The timer thread.
     */
    private final TimerThread thread = new TimerThread(queue);

    // 省略了一些代码 
｝

class TimerThread extends Thread {
    // 省略了一些代码  
}

6、匿名内部类或lambda创建线程，代码示例如下：

public static void main(String[] args) {
    new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println(Thread.currentThread().getName());
        }
    }).start();
}

public static void main(String[] args) {
    new Thread(() -> System.out.println(Thread.currentThread().getName())).start();
}