标签：Thread void System 线程 new 多线程 public

多线程

线程简介

线程就是独立的执行路径
在程序运行时，即使没有自己创建线程，后台也会有多个线程，如主线程，gc线程
main())称之为主线程，为系统的入口，用于执行整个程序
在一个进程中，如果开辟了多个线程，线程的运行由调度器安排调度，调度器是与操作系统紧密相关的，先后顺序是不能人为的干预的
对同一份资源操作时，会存在资源抢夺的问题，需要加入并发控制
线程会带来额外的开销，如cpu调度时间，并发控制开销
每个线程在自己的工作内存交互，内存控制不当会造成数据不一致

线程实现(重点)

线程创建

三种创建方式:

继承Thread类(重点)

/**
 * 创建线程方式一
 * 1.继承Thread类
 * 2.重写run()方法
 * 3.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 Demo01 extends Thread{
    @Override
    public void run() {
        //run方法线程体
        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
        Demo01 demo01 = new Demo01();
        //调用start()方法开启线程
        demo01.start();
        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程-"+i);
        }
    }

}

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;

/**
 * 练习Thread,实现多线程同步下载图片
 */
public class Demo02 extends Thread{
    private  String url; //网络图片地址
    private String name; //保存的文件名

    public Demo02(String url,String name){
        this.url = url;
        this.name = name;
    }

    //下载图片线程的执行体
    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url,name);
        System.out.println("下载了文件名为:"+name);
    }

    public static void main(String[] args) {
        Demo02 d1 = new Demo02("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/1.jpg","1.jpg");
        Demo02 d2 = new Demo02("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/2.jpg","2.jpg");
        Demo02 d3 = new Demo02("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/3.jpg","3.jpg");

        d1.start();
        d2.start();
        d3.start();
    }
}

//下载器
class WebDownloader{
    //下载方法
    public void downloader(String url,String name){
        try {
            FileUtils.copyURLToFile(new URL(url),new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常,downloader方法出现问题");
        }
    }
}

实现Runnable接口(重点)

/**
 * 创建线程方式二
 * 1.实现Runnable接口
 * 2.重写run()方法,执行线程需要丢入Runnable接口实现类
 * 3.调用start()方法
 */
public class Demo01 implements Runnable{
    @Override
    public void run() {
        //run方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("我在看代码-"+i);
        }
    }

    public static void main(String[] args) {
        //创建Runnable接口的实现类对象
        Demo01 demo01 = new Demo01();
        //创建线程对象,通过线程对象来开启我们的线程,代理
        //Thread thread = new Thread(Demo01);
        //thread.start();
        new Thread(demo01).start();
        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程-"+i);
        }
    }
}

龟兔赛跑(案例)

/**
 * 模拟龟兔赛跑
 */
public class Demo03 implements Runnable{
    private static String winner;
    @Override
    public void run() {
        for (int i = 0; i <= 100; i++) {
            //模拟兔子休息
            if (Thread.currentThread().getName().equals("兔子") && i%10 == 0){
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //判断比赛是否结束
            boolean flag = gameOver(i);
            if (flag == true){
                break;
            }
            System.out.println(Thread.currentThread().getName()+"跑了"+i+"步");
        }
    }

    //判断是否完成比赛
    private boolean gameOver(int steps){
        //判断是否有胜利者
        if (winner != null){ //已经存在胜利者了
            return true;
        }{
            if (steps >= 100){
                winner = Thread.currentThread().getName();
                System.out.println("winner is"+winner);
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        Demo03 race = new Demo03();
        new Thread(race,"兔子").start();
        new Thread(race,"乌龟").start();
    }
}

实现Callable接口(了解)
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 = Executor.newFixedThreadPool(1);
5. 提交执行:Future result1 = ser.submit(t1);
6. 获取结果:boolean r1 = result.get();
7. 关闭服务:ser.shutdownNow();

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.*;

/**
 * 线程创建方式三:实现Callable接口
 */
public class Demo01 implements Callable<Boolean> {
    private  String url; //网络图片地址
    private String name; //保存的文件名

    public Demo01(String url,String name){
        this.url = url;
        this.name = name;
    }

    @Override
    public Boolean call() {
        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 {
        Demo01 d1 = new Demo01("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/1.jpg","1.jpg");
        Demo01 d2 = new Demo01("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/2.jpg","2.jpg");
        Demo01 d3 = new Demo01("https://blog.kuangstudy.com/usr/themes/handsome/usr/img/sj/3.jpg","3.jpg");

        //创建执行服务
        ExecutorService ser = Executors.newFixedThreadPool(3);
        //提交执行
        Future<Boolean> r1 = ser.submit(d1);
        Future<Boolean> r2 = ser.submit(d2);
        Future<Boolean> r3 = ser.submit(d3);
        //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
        ser.shutdown();
    }

    //下载器
    class WebDownloader{
        //下载方法
        public void downloader(String url,String name){
            try {
                FileUtils.copyURLToFile(new URL(url),new File(name));
            } catch (IOException e) {
                e.printStackTrace();
                System.out.println("IO异常,downloader方法出现问题");
            }
        }
    }
}

静态代理

/**
 * 静态代理模式总结:
 * 1.真实对象和代理对象都要实现同一个接口
 * 2.代理对象要代理真实角色
 * 好处:
 * 1.代理对象可以做很多真实对象做不了的事情
 * 2.真实对象专注做自己的事情
 */
public class Demo01 {
    public static void main(String[] args) {
        You you = new You(); //你要结婚
        WeddingCompany weddingCompany = new WeddingCompany(you);
        weddingCompany.HappyMarry();
    }

}

interface Marry{
    void HappyMarry();
}

//真实角色,你去结婚
class You implements Marry{

    @Override
    public void HappyMarry() {
        System.out.println("结婚很开心");
    }
}

//代理角色,帮助你结婚
class WeddingCompany implements Marry{

    private Marry target;
    
    public WeddingCompany(Marry target){
        this.target = target;
    }

    @Override
    public void HappyMarry() {
        before();
        this.target.HappyMarry(); //这就是真实对象
        after();
    }

    private void before() {
        System.out.println("结婚之前,布置现场");
    }

    private void after() {
        System.out.println("结婚之后,收尾款");
    }
}

Lambda表达式

好处:

避免匿名内部类定义过多
可以让你的代码看起来很简洁
去掉了一堆没有意义的代码,只留下核心的逻辑

/**
 * 推导Lamda表达式
 */
public class Demo01 {
    //3.静态内部类
    static class Like2 implements ILike{

        @Override
        public void lamda() {
            System.out.println("i like lamda2");
        }
    }

    public static void main(String[] args) {
        Like1 like1 = new Like1();
        like1.lamda();
        Like2 like2 = new Like2();
        like2.lamda();

        //4.局部内部类
        class Like3 implements ILike{

            @Override
            public void lamda() {
                System.out.println("i like lamda3");
            }
        }
        Like3 like3 = new Like3();
        like3.lamda();

        //5.匿名内部类:没有类的名称,必须借助接口或者父类
        ILike like = new ILike() {

            @Override
            public void lamda() {
                System.out.println("i like lamda4");
            }
        };
        like.lamda();

        //6.用lamda简化
        like = ()->{
            System.out.println("i like lamda5");
        };
        like.lamda();
    }
}

/**
 * 总结:
 * 1.lambda表达式只能有一行代码的情况下才能简化成一行,如果有多行,那么就用代码块包裹
 * 2.前提是接口为函数式接口
 * 3.多个参数也可以去掉参数类型,要去掉都去掉,必须加上括号
 */
public class Demo02 {
    public static void main(String[] args) {
        //1.lambda表示简化
        ILove love = (int a) -> {
            System.out.println("i love you"+a);
        };
        //简化1.参数类型
        love = (a) -> {
            System.out.println("i love you"+a);
        };
        //简化2.简化括号
        love = a -> {
            System.out.println("i love you"+a);
        };
        //简化3.去掉花括号
        love = a -> System.out.println("i love you"+a);
        love.love(2);
    }
}

interface ILove{
    void love(int a);
}

线程状态

多线程-线程状态

方法	说明
setPriority(int newPriority)	更改线程的优先级
static void sleep(long millis)	在指定的毫秒数内让当前正在执行的线程休眠
void join()	等待该线程终止
static void yield()	暂停当前正在执行的线程对象,并执行其他线程
void interrupt()	中断线程,别用这个方式
boolean isAlive()	测试线程是否处于活动状态

线程停止

/**
 * 测试stop
 * 1.建议线程正常停止-->利用次数,不建议死循环
 * 2.建议使用标志位-->设置一个标志位
 * 3.不要使用stop或者destroy等过时或者JDK不建议使用的方法
 */
public class Demo01 implements Runnable{
    //1.设置一个标志位
    private boolean flag = true;
    @Override
    public void run() {
        int i = 0;
        while (flag){
            System.out.println(i++);
        }
    }
    //2.设置一个公开的方法停止线程,转换标志位
    public void stop(){
        this.flag = false;
    }

    public static void main(String[] args) {
        Demo01 demo01 = new Demo01();
        new Thread(demo01).start();
        for (int i = 0; i < 1000; i++) {
            System.out.println("main"+i);
            if (i == 900){
                //调用stop方法切换标志位,让线程停止
                demo01.stop();
                System.out.println("线程停止");
            }
        }
    }
}

线程休眠

public class Demo02 implements Runnable{
    //票数
    private int ticketNums = 10;

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

    public static void main(String[] args) {
        Demo02 ticket = new Demo02();
        new Thread(ticket,"小明").start();
        new Thread(ticket,"小红").start();
        new Thread(ticket,"小强").start();
    }
}

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * 模拟倒计时
 */
public class Demo03 {
    public static void main(String[] args) throws InterruptedException {
        //tenDown();

        //打印当前系统时间
        Date date = new Date(System.currentTimeMillis()); //获取当前时间
        while (true){
            Thread.sleep(1000);
            System.out.println(new SimpleDateFormat("HH:mm:ss").format(date));
            date = new Date(System.currentTimeMillis());
        }
    }
    public static void tenDown() throws InterruptedException {
        int num = 10;
        while (true){
            Thread.sleep(1000);
            System.out.println(num--);
            if (num<=0){
                break;
            }
        }
    }
}

线程礼让

/**
 * 测试礼让线程
 * 礼让不一定成功,看CPU心情
 */
public class Demo04 {
    public static void main(String[] args) {
        MyYield myYield = new MyYield();
        new Thread(myYield,"a").start();
        new Thread(myYield,"b").start();
    }
}

class MyYield implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"线程开始执行");
        Thread.yield();
        System.out.println(Thread.currentThread().getName()+"线程停止执行");
    }
}

线程强制执行

public class Demo05 implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("线程vip来了"+i);
        }
    }

    public static void main(String[] args) throws InterruptedException {
        //启动线程
        Demo05 demo05 = new Demo05();
        new Thread(demo05).start();

        //主线程
        for (int i = 0; i < 500; i++) {
            if (i == 200){
                new Thread().join();
            }
            System.out.println("main线程"+i);
        }
    }
}

观测线程状态

/**
 * 观察测试线程的状态
 */
public class Demo06 {
    public static void main(String[] args) {
        Thread thread = new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("/////");
        });

        //观察状态
        Thread.State state = thread.getState();
        System.out.println(state);

        //观察启动后
        thread.start();
        state = thread.getState();
        System.out.println(state);

        while (state != Thread.State.TERMINATED){ //只要线程不停止,就一直输出状态
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            state = thread.getState(); //更新线程状态
            System.out.println(state); //输出状态
        }
    }
}

线程优先级

/**
 * 测试线程的优先级
 */
public class Demo07 {
    public static void main(String[] args) {
        //主线程默认优先级
        System.out.println(Thread.currentThread().getName()+"-->"+Thread.currentThread().getPriority());
        MyPriority myPriority = new MyPriority();
        Thread t1 = new Thread(myPriority);
        Thread t2 = new Thread(myPriority);
        Thread t3 = new Thread(myPriority);

        //先设置优先级,在启动
        t1.start();

        t2.setPriority(Thread.MAX_PRIORITY);
        t2.start();

        t3.setPriority(4);
        t3.start();
    }
}

class MyPriority implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"-->"+Thread.currentThread().getPriority());
    }
}

守护(deamon)线程

/**
 * 测试守护线程
 */
public class Demo08 {
    public static void main(String[] args) {
        God god = new God();
        You you = new You();

        Thread thread = new Thread(god);
        thread.setDaemon(true); //默认是false表示用户线程,正常的线程都是用户线程
        thread.start();

        new Thread(you).start();
    }
}

class You implements Runnable{

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("hello world");
        }
        System.out.println("goodbye world");
    }
}

class God implements Runnable{

    @Override
    public void run() {
        while (true){
            System.out.println("上帝保佑");
        }
    }
}

线程同步(重点)

并发:同一个对象被多个线程同时操作

同步块

同步块:synchronized(obj){}

Obj称之为同步监视器

Obj可以是任何对象,但是推荐使用共享资源作为同步监视器
同步方法中无需指定同步监视器,因为同步方法的同步监视器就是this,就是这个对象本身,或者是class[反射中讲解]

同步监视器的执行过程

第一个线程访问,锁定同步监视器,执行其中代码
第二个线程访问,发现同步监视器被锁定,无法访问
第一个线程访问完毕,解锁同步监视器
第二个线程访问,发现同步监视器没有锁,然后锁定并访问

/**
 * 不安全的买票
 * 线程不安全,有负数
 */
public class Demo01 {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
        Thread t1 = new Thread(buyTicket, "我");
        Thread t2 = new Thread(buyTicket,"你");
        Thread t3 = new Thread(buyTicket,"他");

        t1.start();
        t2.start();
        t3.start();
    }
}

class BuyTicket implements Runnable{
    //票
    private int ticketNum = 10;
    boolean flag = true;

    @Override
    public void run() {
        //买票
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            ;
        }
    }

    private synchronized void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNum <= 0){
            flag = false;
            return;
        }
        //模拟延时
        Thread.sleep(100);
        System.out.println(Thread.currentThread().getName()+"拿到了第"+ticketNum--+"张票");
    }
}

/**
 * 不安全的取钱
 * 两个人去银行取钱,账户
 */
public class Demo02 {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100,"结婚基金");
        Drawing you = new Drawing(account,50,"你");
        Drawing she = new Drawing(account,100,"她");
        you.start();
        she.start();
    }
}

//账户
class Account{
    int money; //余额
    String name; //卡名

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}

//银行
class Drawing extends Thread{
    Account account;
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;

    public Drawing(Account account,int drawingMoney,String name){
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;
    }

    //取钱
    @Override
    public void run() {
        synchronized (account) {
            //判断有没有钱
            if (account.money - drawingMoney < 0) {
                System.out.println(Thread.currentThread().getName() + "钱不够,取不了");
                return;
            }

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //卡内余额 = 余额 - 你取的钱
            account.money = account.money - drawingMoney;
            //你手里的钱
            nowMoney = nowMoney + drawingMoney;

            System.out.println(account.name + "余额为" + account.money);
            System.out.println(this.getName() + "手里的钱" + nowMoney);
        }
    }
}

import java.util.ArrayList;

/**
 * 线程不安全的集合
 */
public class Demo03 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        for (int i = 0; i < 1000; i++) {
            new Thread(() -> {
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

死锁

产生死锁的四个必要条件:

互斥条件:一个资源每次只能被一个进程使用
请求与保持条件:一个进程因请求资源而阻塞时,对已获得的资源保持不放
不剥夺条件:进程已获得的资源,在未使用完之前,不能强行剥夺
循环等待条件:若干进程之间形成一种头尾相接的循环等待资源关系

/**
 * 死锁:多个线程互相抱着对方需要的资源,然后形成僵持
 */
public class Demo05 {
    public static void main(String[] args) {
        Makeup g1 = new Makeup(0,"ggg");
        Makeup g2 = new Makeup(1,"yyy");
        g1.start();
        g2.start();
    }
}

//口红
class Lipstick{

}

//镜子
class Mirror{

}

class Makeup extends Thread{
    static Lipstick lipstick = new Lipstick();
    static Mirror mirror = new Mirror();

    int choice;
    String girlName;

    Makeup(int choice,String girlName){
        this.choice = choice;
        this.girlName = girlName;
    }

    @Override
    public void run() {
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //化妆,互相持有对方的锁,就是需要拿到对方的资源
    private void makeup() throws InterruptedException {
        if (choice == 0){
            synchronized (lipstick){
                System.out.println(this.girlName+"获得口红的锁");
                Thread.sleep(1000);
                }
            synchronized (mirror){ //一秒钟后想获得镜子
                System.out.println(this.girlName+"获得镜子的锁");
            }
        }else {
            synchronized (mirror){
                System.out.println(this.girlName+"获得镜子的锁");
                Thread.sleep(2000);
                }
            synchronized (lipstick){ //两秒钟后想获得口红
                System.out.println(this.girlName+"获得口红的锁");
            }
        }
    }
}

Lock锁

synchronized与 Lock 的对比:

Lock是显式锁(手动开启和关闭锁,别忘记关闭锁),synchronized是隐式锁，出了作用域自动释放
Lock只有代码块锁,synchronized有代码块锁和方法锁
使用Lock锁,JVM将花费较少的时间来调度线程,性能更好.并且具有更好的扩展性(提供更多的子类)
优先使用顺序:
Lock >同步代码块 (已经进入了方法体,分配了相应资源)>同步方法(在方法体之外)

import java.util.concurrent.locks.ReentrantLock;

/**
 * 测试Lock锁
 */
public class Demo01 {
    public static void main(String[] args) {
        Lock lock = new Lock();
        new Thread(lock).start();
        new Thread(lock).start();
        new Thread(lock).start();
    }
}

class Lock implements Runnable{
    int ticketNum = 10;

    //定义Lock锁
    private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true){
            try{
                //加锁
                lock.lock();
                if (ticketNum > 0){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(ticketNum--);
                }else{
                    break;
                }
            }finally {
                //解锁
                lock.unlock();
            }


        }
    }
}

线程通信问题

Java提供了几个方法解决线程之间的通信问题

方法名	作用
wait()	表示线程一直等待,直到其他线程通知,与sleep不同,会释放锁
wait(long timeout)	指定等待的毫秒数
notify()	唤醒一个处于等待状态的线程
notifyAll()	唤醒同一个对象上所有调用wait()方法的线程,优先级别高的线程优先调度

注意:均是Object类的方法,都只能在同步方法或者同步代码块中使用,否则会抛出异常IIIegalMonitorStateException

/**
 * 测试生产者消费者模型
 * 管程法:利用缓冲区解决
 */
public class Demo01 {
    public static void main(String[] args) {
        SynContainer container = new SynContainer();
        new Productor(container).start();
        new Consumer(container).start();
    }
}

//生产者
class Productor extends Thread{
    SynContainer container;
    public Productor(SynContainer container){
        this.container = container;
    }

    //生产
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            container.push(new Chicken(i));
            System.out.println("生产了"+i+"只鸡");
        }
    }
}

//消费者
class Consumer extends Thread{
    SynContainer container;
    public Consumer(SynContainer container){
        this.container = container;
    }

    //消费
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("消费了"+container.pop().id+"只鸡");
        }
    }
}

//产品
class Chicken{
    int id;

    public Chicken(int id) {
        this.id = id;
    }
}

//缓冲区
class SynContainer{
    //需要一个容器大小
    Chicken[] chickens = new Chicken[10];

    //容器计数器
    int count = 0;

    //生产者放入产品
    public synchronized void push(Chicken chicken){
        //如果容器满了,就需要等待消费者消费
        if (count == chickens.length){
            //通知消费者消费
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //如果没有满,我们就需要丢入产品
        chickens[count] = chicken;
        count++;

        //可以通知消费者消费了
        this.notifyAll();
    }

    //消费者消费产品
    public synchronized Chicken pop(){
        //判断能否消费
        if (count == 0){
            //等待生产者生产,消费者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        //如果可以消费
        count--;
        Chicken chicken = chickens[count];

        //吃完了,通知生产者生产
        this.notifyAll();
        return chicken;
    }
}

/**
 * 测试生产者消费者2
 * 信号灯法:标志位解决
 */
public class Demo02 {
    public static void main(String[] args) {
        TV tv = new TV();
        new Player(tv).start();
        new Watcher(tv).start();
    }
}

//生产者->演员
class Player extends Thread{
    TV tv;
    public Player(TV tv){
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            if (i%2 == 0){
                this.tv.play("11111");
            }else{
                this.tv.play("22222");
            }
        }
    }
}

//消费者->观众
class Watcher extends Thread{
    TV tv;
    public Watcher(TV tv){
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            tv.watch();
        }
    }
}

//产品->节目
class TV{
    //演员表演,观众等待
    //观众观看,演员等待
    String voice; //表演的节目
    boolean flag = true;

    //表演
    public synchronized void play(String voice){
        if (!flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("演员表演了"+voice);
        //通知观众观看
        this.notifyAll(); //通知唤醒
        this.voice = voice;
        this.flag = !this.flag;
    }

    //观看
    public synchronized void watch(){
        if (flag){
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("观众观看了"+voice);
        //通知演员表演
        this.notifyAll();
        this.flag = !this.flag;
    }
}

线程池

背景:经常创建和销毁.使用量特别大的资源,比如并发情况下的线程,对性能影响很大

思路:提前创建好多个线程,放入线程池中,使用时直接获取,使用完放回池中可以避免频繁创建销毁.实现重复利用.类似生活中的公共交通工具

好处:

提高响应速度(减少了创建新线程的时间)
降低资源消耗(重复利用线程池中线程，不需要每次都创建)
便于线程管理(...)
- corePoolSize:核心池的大小
- maximumPoolSize: 最大线程数
- keepAliveTime: 线程没有任务时最多保持多长时间后会终止

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 测试线程池
 */
public class Demo01 {
    public static void main(String[] args) {
        //1.创建服务,创建线程池
        //newFixedThreadPool 参数为:线程池大小
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        //执行
        executorService.execute(new MyThread());
        executorService.execute(new MyThread());
        executorService.execute(new MyThread());
        //2.关闭链接
        executorService.shutdown();
    }
}

class MyThread implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

标签：Thread,void,System,线程,new,多线程,public
From： https://www.cnblogs.com/gy486926/p/17596736.html

多线程

多线程