Java多线程——线程实现的三种方式

Java多线程——线程实现的三种方式 线程的三种创建方式

1.继承Thread类

例子1
// 创建方式一：继承Thread类，重写run()方法  调用start开启线程
public class TestThread01 extends  Thread{
	@Override
	public void run() {
		for (int i = 0; i < 20; i++) {
			System.out.println("我在看代码"+i);
		}
	}

	public static void main(String[] args) {
		//main线程  主线程

		//创建一个线程对象
		TestThread01 testThread01 = new TestThread01();
		//调用start开启线程
		testThread01.start();

		for (int i = 0; i < 2000; i++) {
			System.out.println("我在学习多线程"+i);
		}
	}
}

调用start()线程之间交替执行

调用run()和start()的区别

例子2：
//实现多线程同步下载图片
public class TestThread02 extends Thread{
	private String url;
	private String name;

	public TestThread02(String url,String name){
		this.url = url;
		this.name = name;
	}

	//下载图片线程的执行体
	@Override
	public void run() {
		TestThread02 t1 = new TestThread02("https://t7.baidu.com/it/u=4240641596,3235181048&fm=193&f=GIF", "1.jpg");
		TestThread02 t2 = new TestThread02("https://t7.baidu.com/it/u=1951548898,3927145&fm=193&f=GIF", "2.jpg");
		TestThread02 t3 = new TestThread02("https://t7.baidu.com/it/u=1831997705,836992814&fm=193&f=GIF", "3.jpg");
		t1.start();
		t2.start();
		t3.start();
	}
}

class WebDownLoader{
	public void downloader(String url,String name){
		try {
			FileUtils.copyURLToFile(new URL(url),new File(name));
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

2.实现Runnable接口

//创建线程方式二：实现runnable接口，重写run方法
public class TestThread03 implements Runnable {
	@Override
	public void run() {
		for (int i = 0; i < 20; i++) {
			System.out.println("我在看代码"+i);
		}
	}
	public static void main(String[] args) {
		//main线程  主线程

		//创建runnable接口的实现类对象
		TestThread03 testThread03 = new TestThread03();
		//创建线程对象，通过线程对象来开启线程，代理
		Thread thread = new Thread(testThread03);
		thread.start();

		for (int i = 0; i < 100; i++) {
			System.out.println("我在学习多线程"+i);
		}
	}
}

多个线程同时 *** 作同一个对象 买火车票的例子

//发现问题：多个线程 *** 作同一个资源的情况下线程不安全，数据紊乱， 不同的人可以拿到同一张票（看打印结果）
public class TestThread04 implements Runnable{
	private int ticketNums = 10;

	@Override
	public void run() {
		while (true){
			if (ticketNums <= 0){
				break;
			}
			try {
				Thread.sleep(200);//模拟延时
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName()+"-->拿到了第"+ticketNums--+"票");
		}
	}

	public static void main(String[] args) {
		TestThread04 testThread04 = new TestThread04();
		new Thread(testThread04,"小明").start();
		new Thread(testThread04,"老师").start();
		new Thread(testThread04,"黄牛党").start();
	}
}

上述线程存在不安全性，想要线程安全请看另一篇博客 ：线程同步安全

3.实现Callable接口

/线程创建方式三：实现callable接口
	//可以定义返回值
	//可以抛出异常
public class TestThread05 implements Callable {
	private String url;
	private String name;

	public TestThread05(String url,String name){
		this.url = url;
		this.name = name;
	}

	//下载图片线程的执行体
	@Override
	public Boolean call() throws Exception {
		WebDownLoader webDownLoader = new WebDownLoader();
		webDownLoader.downloader(url,name);
		System.out.println("下载了文件名为："+name);
		return true;
	}

	public static void main(String[] args) throws ExecutionException, InterruptedException {
		TestThread05 t1 = new TestThread05("https://t7.baidu.com/it/u=4240641596,3235181048&fm=193&f=GIF", "1.jpg");
		TestThread05 t2 = new TestThread05("https://t7.baidu.com/it/u=1951548898,3927145&fm=193&f=GIF", "2.jpg");
		TestThread05 t3 = new TestThread05("https://t7.baidu.com/it/u=1831997705,836992814&fm=193&f=GIF", "3.jpg");

		//创建执行服务
		ExecutorService executorService = Executors.newFixedThreadPool(3);

		//提交执行
		Future r1 = executorService.submit(t1);
		Future r2 = executorService.submit(t2);
		Future r3 = executorService.submit(t3);

		//获取结果
		Boolean rs1 = r1.get();
		Boolean rs2 = r2.get();
		Boolean rs3 = r3.get();
		System.out.println(rs1);
		System.out.println(rs2);
		System.out.println(rs3);

		//关闭服务
		executorService.shutdownNow();
	}
}

注意：线程开启不一定立即执行，由CPU调度执行