java创建线程有四个方法： 1.继承Thread类 2.实现Runnable接口 3.实现Callable接口 4.创建线程池

分别用四种创建线程的方式计算1到100之间偶数的和

1.继承Thread类

public class ThreadTest {
    public static void main(String[] args) {
        sumTest sumTest= new sumTest();
        sumTest.run();
    }

}
class sumTest extends Thread{
    @Override
    public void run() {
        int sum = 0 ;
        for (int i = 0; i <= 100; i++) {
            if (i % 2 == 0) {
                sum += i;
            }

        }
        System.out.println(sum);
    }
}

2.实现Runnable接口

public class RunnableTest {
    public static void main(String[] args) {
        runnable1 runnable1 = new runnable1();
        new Thread(runnable1).start();

    }
}

class runnable1 implements Runnable {

    @Override
    public void run() {

        int sum = 0;
        for (int i = 0; i <= 100; i++) {
            if (i % 2 == 0) {
                sum += i;
            }

        }
        System.out.println(sum);

    }
}

3.实现Callable接口

public class CallableTest {
    public static void main(String[] args) {
        callable1 callable1 = new callable1();
        //1.实例化futureTask
        FutureTask futureTask = new FutureTask(callable1);
        //2.将futureTask放入线程中去启动
        new Thread(futureTask).start();
        try {
            System.out.println(futureTask.get());//3.get接收返回值(可不需要返回值)
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
}
class callable1 implements Callable {


    @Override
    public Object call() throws Exception {
        int sum = 0;
        for (int i = 0; i <= 100; i++) {
            if (i % 2 == 0) {
                sum+= i;
            }

        }
        return sum;//会自动装箱
    }
}

4.创建线程池

public class ThreadPoll {
    public static void main(String[] args) {
        //1.创建线程池可容纳最多的线程数量
        ExecutorService service = Executors.newFixedThreadPool(10);
        //2.调用execute方法（适合用实现runnable接口的类，callable用的是submit方法）
        //3.传入实现了runnable接口的类
        service.execute(new threadPool());
        //4.关闭连接池
        service.shutdown();
    }
}
class threadPool implements Runnable{

    @Override
    public void run() {
        int sum = 0 ;
        for (int i = 0; i <= 100; i++) {
            if (i % 2 == 0) {
                sum += i;
            }

        }
        System.out.println(sum);
    }
}

4.1，三种Excuutors方式

public class ThreadPool {
    public static void main(String[] args) {
//        ExecutorService service = Executors.newSingleThreadExecutor();//单个线程，只有一个线程在执行
//        ExecutorService service = Executors.newFixedThreadPool(5);//固定线程，指定线程数
        ExecutorService service = Executors.newCachedThreadPool();//可变线程数，有多少来多少
        try {
            for (int i = 0; i < 10; i++) {
                service.execute(()->{
                    System.out.println(Thread.currentThread().getName());
                });
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            service.shutdown();
        }
    }
}