多线程的三种创建方法

继承Thread类
    子类继承Thread类具备多线程能力
    启动线程:子类对象. start()
            
实现接口Runnable
    启动线程:传入目标对象+ Thread对象.start()
    推荐使用:避免单继承局限性，灵活方便，方便同一个对象被多个线程使用

实现Callable接口
    1.实现Callable接口，需要返回值类型
    2.重写call方法，需要抛出异常
    3.创建目标对象
    4.创建执行服务: ExecutorService ser = Executors.newFixedThreadPool(1);
    5.提交执行: Future<Boolean> result1 = ser.submit(t1);
    6.获取结果: boolean r1 = result1.get()
    7.关闭服务: ser.shutdownNow();

使用Callable接口好处：
    1、可以定义返回值
    2、可以抛出异常

//创建线程方式一：继承Thread类，重写run()方法，调用start开启线程
//注意，线程开启不一定立即执行，由CPU调度执行
public class ThreadTest extends Thread{
    public void run(){
        //run方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("run方法");
        }
    }
    public static void main(String[] args) {
        //main线程，主线程
        //创建一个线程对象
        ThreadTest threadTest = new ThreadTest();
        threadTest.run();//调用start方法，同时执行，调用run方法，顺序执行
        for (int i = 0; i < 20; i++) {
            System.out.println("主线程");
        }
    }
}

//创建线程方式二：实现Runnable接口，重写run()方法，执行线程需要丢入Runnable实现类接口，调用Start方法
public class ThreadTest1 implements Runnable {
    public void run(){
        //run方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("run方法");
        }
    }
    public static void main(String[] args) {
        //创建Runnable线程接口的实现类对象
        ThreadTest1 threadTest1 = new ThreadTest1();
        //创建线程对象,通过线程对象来开启我们的线程,代理
        new Thread(threadTest1).start();
        for (int i = 0; i < 20; i++) {
            System.out.println("主线程");
        }
    }
}

import java.util.concurrent.*;

//线程创建方法三,实现Callable接口
public class CallableTest implements Callable<Boolean> {
    private String s;

    public CallableTest(String s) {
        this.s=s;
    }
    @Override
    public Boolean call(){//重写call方法
            System.out.println(s);
        return true;
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CallableTest c1 = new CallableTest("1");
        CallableTest c2 = new CallableTest("2");
        CallableTest c3 = new CallableTest("3");
        CallableTest c4 = new CallableTest("4");
        CallableTest c5 = new CallableTest("5");
        CallableTest c6 = new CallableTest("6");
        //创建执行服务:
        ExecutorService ser = Executors.newFixedThreadPool(6);
        //提交执行:
        Future<Boolean> r1 = ser.submit(c1);
        Future<Boolean> r2 = ser.submit(c2);
        Future<Boolean> r3 = ser.submit(c3);
        Future<Boolean> r4 = ser.submit(c4);
        Future<Boolean> r5 = ser.submit(c5);
        Future<Boolean> r6 = ser.submit(c6);
        //获取结果:
        boolean rs1 = r1.get();
        boolean rs2 = r2.get();
        boolean rs3 = r3.get();
        boolean rs4 = r3.get();
        boolean rs5 = r3.get();
        boolean rs6 = r3.get();
        //7. 关闭服务:
        ser.shutdownNow();
    }
}