一文带你搞懂Java中线程的创建方式

public class ThreadTest {

    @Test
    public void 继承Thread() throws Exception {
        // 创建线程对象
        MyThread myThread = new MyThread();

        // 启动线程
        myThread.start();

        // 睡1秒，等待子线程执行完任务
        Thread.sleep(1000);
    }

    private static class MyThread extends Thread {
        @Override
        public void run() {
            System.out.println("线程执行了");
        }
    }

}

public class ThreadTest {

    @Test
    public void 继承Thread时可以不重写run方法() {
        // 创建没有重写run()方法的线程对象
        MyThreadNotOverrideRun myThread = new MyThreadNotOverrideRun();

        // 启动线程，不报错，执行的是Thread的run()方法，无任何逻辑
        myThread.start();
    }

    private static class MyThreadNotOverrideRun extends Thread {}

}

public class ThreadTest {

    @Test
    public void 基于Runnable() throws Exception {
        // 创建Runnable任务对象
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println("任务执行");
            }
        };

        // 创建Thread对象时将Runnable任务对象通过构造函数传入
        Thread thread = new Thread(runnable);

        // 启动线程
        thread.start();

        // 睡1秒，等待子线程执行完任务
        Thread.sleep(1000);
    }

}

public class ThreadTest {

    @Test
    public void 基于Callable() throws Exception {
        // 创建Callable任务对象
        Callable<String> callable = new Callable<String>() {
            @Override
            public String call() throws Exception {
                return "任务执行结果";
            }
        };

        // 将Callable封装成FutureTask
        FutureTask<String> futureTask = new FutureTask<>(callable);

        // 创建Thread对象时将FutureTask通过构造函数传入
        Thread thread = new Thread(futureTask);

        // 启动线程
        thread.start();

        // 通过FutureTask拿到执行结果
        System.out.println(futureTask.get());
    }

}

// 基于Callable创建FutureTask
public FutureTask(Callable<V> callable)

// 基于Runnable创建FutureTask
public FutureTask(Runnable runnable, V result)

public FutureTask(Runnable runnable, V result) {
    // 使用Executors工具类将Runnable封装成Callable
    this.callable = Executors.callable(runnable, result);
    this.state = NEW;
}

public static <T> Callable<T> callable(Runnable task, T result) {
    if (task == null) {
        throw new NullPointerException();
    }
    // 将Runnable封装成RunnableAdapter
    return new RunnableAdapter<T>(task, result);
}

static final class RunnableAdapter<T> implements Callable<T> {
    final Runnable task;
    final T result;
    
    RunnableAdapter(Runnable task, T result) {
        this.task = task;
        this.result = result;
    }
    
    public T call() {
        // 执行Runnable的逻辑
        task.run();
        // 执行完毕后，result作为结果返回
        return result;
    }
}

public class ThreadTest {

    @Test
    public void 基于Runnable来构建FutureTask() throws Exception {
        // 创建结果对象
        MyResult myResult = new MyResult();
        // 创建Runnable任务对象
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                myResult.setResult("任务执行");
            }
        };

        // 将Runnable封装成FutureTask
        // Runnable执行后，会改变MyResult对象
        FutureTask<MyResult> futureTask = new FutureTask<>(runnable, myResult);

        // 创建Thread对象时将FutureTask通过构造函数传入
        Thread thread = new Thread(futureTask);

        // 启动线程
        thread.start();

        // 通过FutureTask拿到执行结果
        System.out.println(futureTask.get().getResult());
    }

    private static class MyResult {
        String result;

        public MyResult() {}

        public MyResult(String result) {
            this.result = result;
        }

        public String getResult() {
            return result;
        }

        public void setResult(String result) {
            this.result = result;
        }
    }

}