多线程（总结完毕） 2020.12.24

1.简介

进程是程序的最小单位，线程是资源调度的最小单位

Process 进程

Thread 线程

2.线程的三种创建方式

2.1继承Thread类，重写run方法

package com.liang.demo01;

//创建线程方式一：继承Thread类，重写run（）方法，调用start开启线程
public class TestThread1 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

        //调用一个线程对象
        TestThread1 testThread1 = new TestThread1();

        //调用start（）方法开启线程 同时执行
        //如果在这里调用run方法的话就直接运行run方法再到下面，而不是多线程了
        testThread1.start();

        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程==" + i);
        }
    }
}

总结：注意，线程开启不一定立即执行，由CPU调度执行

2.2练习Thread，实现多线程同步下载图片

            <artifactId>commons-io</artifactId>

            <artifactId>commons-io</artifactId>

package com.liang.demo01;

import org.apache.commons.io.FileUtils;

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

//练习Thread，实现多线程同步下载图片
public class TestThread2 extends Thread{

    private String url;//网络图片地址
    private String name;//保存的文件名

    //创建一个构造器
    public TestThread2(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) {
        TestThread2 t1 = new TestThread2("https://i0.hdslb.com/bfs/sycp/creative_img/202012/b0cf49625b263677ea4d2c3476496707.jpg@880w_388h_1c_95q","1.jpg");
        TestThread2 t2 = new TestThread2("https://i0.hdslb.com/bfs/sycp/creative_img/202012/b0cf49625b263677ea4d2c3476496707.jpg@880w_388h_1c_95q","2.jpg");
        TestThread2 t3 = new TestThread2("https://i0.hdslb.com/bfs/sycp/creative_img/202012/b0cf49625b263677ea4d2c3476496707.jpg@880w_388h_1c_95q","3.jpg");
        //先下载t1
        t1.start();
       //然后是t2
        t2.start();
        //最后是t3
        t3.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方法出现异常问题");
        }
    }
}

2.3实现runnable接口，重写run方法

package com.liang.demo01;

//创建线程方式2：实现runnable接口，重写run方法，执行线程需要丢入runnable接口实现类，调用start方法
public class TestThread3 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

        TestThread3 testThread3 = new TestThread3();

        //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(testThread3);
//
//        thread.start();

        new Thread(testThread3).start();

        for (int i = 0; i < 202; i++) {
            System.out.println("我在学习多线程==" + i);
        }
    }
}

小结：

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
• 不建议使用：避免oop 单继承局限性

实现Runnable接口

• 实现接口Runnable具有多线程能力
• 启动多线程：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，方便同一个人对象被多个线程使用

2.4模拟多线程抢火车票

package com.liang.demo01;
//多个线程操作同一个对象
//买火车票的例子


//发现问题：多个线程操作同一个资源的时候，线程不安全，混乱
public class TestThread4 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-- + "票");

        }
    }

    public static void main(String[] args) {

        TestThread4 ticket = new TestThread4();
        new Thread(ticket,"小号").start();
        new Thread(ticket,"姐姐").start();
        new Thread(ticket,"康康").start();
    }
}

输出结果：D:\JavaEnvironment\jdk1.8.0_152\bin\java.exe "-javaagent:D:\Study software\IntelliJ IDEA 2020.3\lib\idea_rt.jar=51491:D:\Study software\IntelliJ IDEA 2020.3\bin" -Dfile.encoding=UTF-8 -classpath D:\JavaEnvironment\jdk1.8.0_152\jre\lib\charsets.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\deploy.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\access-bridge-64.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\cldrdata.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\dnsns.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\jaccess.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\jfxrt.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\localedata.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\nashorn.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\sunec.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\sunjce_provider.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\sunmscapi.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\sunpkcs11.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\ext\zipfs.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\javaws.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\jce.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\jfr.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\jfxswt.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\jsse.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\management-agent.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\plugin.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\resources.jar;D:\JavaEnvironment\jdk1.8.0_152\jre\lib\rt.jar;D:\IdeaWorkSpace2\kuangshen\Thread\target\classes;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-starter-web\2.3.4.RELEASE\spring-boot-starter-web-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-starter\2.3.4.RELEASE\spring-boot-starter-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot\2.3.4.RELEASE\spring-boot-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-autoconfigure\2.3.4.RELEASE\spring-boot-autoconfigure-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-starter-logging\2.3.4.RELEASE\spring-boot-starter-logging-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;D:\JavaEnvironment\maven\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;D:\JavaEnvironment\maven\org\apache\logging\log4j\log4j-to-slf4j\2.13.3\log4j-to-slf4j-2.13.3.jar;D:\JavaEnvironment\maven\org\apache\logging\log4j\log4j-api\2.13.3\log4j-api-2.13.3.jar;D:\JavaEnvironment\maven\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;D:\JavaEnvironment\maven\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;D:\JavaEnvironment\maven\org\yaml\snakeyaml\1.26\snakeyaml-1.26.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-starter-json\2.3.4.RELEASE\spring-boot-starter-json-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\core\jackson-databind\2.11.2\jackson-databind-2.11.2.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\core\jackson-annotations\2.11.2\jackson-annotations-2.11.2.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\core\jackson-core\2.11.2\jackson-core-2.11.2.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.11.2\jackson-datatype-jdk8-2.11.2.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.11.2\jackson-datatype-jsr310-2.11.2.jar;D:\JavaEnvironment\maven\com\fasterxml\jackson\module\jackson-module-parameter-names\2.11.2\jackson-module-parameter-names-2.11.2.jar;D:\JavaEnvironment\maven\org\springframework\boot\spring-boot-starter-tomcat\2.3.4.RELEASE\spring-boot-starter-tomcat-2.3.4.RELEASE.jar;D:\JavaEnvironment\maven\org\apache\tomcat\embed\tomcat-embed-core\9.0.38\tomcat-embed-core-9.0.38.jar;D:\JavaEnvironment\maven\org\glassfish\jakarta.el\3.0.3\jakarta.el-3.0.3.jar;D:\JavaEnvironment\maven\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.38\tomcat-embed-websocket-9.0.38.jar;D:\JavaEnvironment\maven\org\springframework\spring-web\5.2.9.RELEASE\spring-web-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-beans\5.2.9.RELEASE\spring-beans-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-webmvc\5.2.9.RELEASE\spring-webmvc-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-aop\5.2.9.RELEASE\spring-aop-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-context\5.2.9.RELEASE\spring-context-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-expression\5.2.9.RELEASE\spring-expression-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\commons-io\commons-io\2.6\commons-io-2.6.jar;D:\JavaEnvironment\maven\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;D:\JavaEnvironment\maven\org\springframework\spring-core\5.2.9.RELEASE\spring-core-5.2.9.RELEASE.jar;D:\JavaEnvironment\maven\org\springframework\spring-jcl\5.2.9.RELEASE\spring-jcl-5.2.9.RELEASE.jar com.liang.demo01.TestThread4
康康-->拿到了第9票
小号-->拿到了第8票
姐姐-->拿到了第10票
姐姐-->拿到了第7票
小号-->拿到了第6票
康康-->拿到了第6票
小号-->拿到了第5票
康康-->拿到了第4票
姐姐-->拿到了第4票
小号-->拿到了第3票
康康-->拿到了第3票
姐姐-->拿到了第3票
小号-->拿到了第2票
康康-->拿到了第2票
姐姐-->拿到了第2票
康康-->拿到了第1票
姐姐-->拿到了第1票
小号-->拿到了第1票

Process finished with exit code 0
出现了重票

2.5 模拟多线程龟兔赛跑

package com.liang.demo01;

//模拟龟兔赛跑
public class Race implements Runnable {
//胜利者
    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(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }


            //判断比赛是否结束
            boolean flag = gameOver(i);
            //如果比赛结束了，就停止程序
        if (flag){
            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) {
        Race race = new Race();

        new Thread(race,"兔子").start();
        new Thread(race,"乌龟").start();
    }
}

2.6 实现callable接口

3.静态代理

静态代理模式总结：真实对象和代理模式对象都要实现同一个接代理对象要代理真实角色
好处：
代理对象可以做很多真是对象做不了的事情
真实对象专注做自己的事情

import javax.xml.ws.WebEndpoint;
import java.lang.annotation.Target;


//静态代理模式总结
//真实对象和代理模式对象都要实现同一个接口
//代理对象要代理真实角色

        //好处：
            //代理对象可以做很多真是对象做不了的事情
            //真实对象专注做自己的事情

public class StaticProxy {
    public static void main(String[] args) {

        new Thread(()-> System.out.println("我爱你")).start();//lombok表达式

        new WeddingCompany( new You()).HappyMarry();


//      You you = new You();//你要结婚
//
//        WeddingCompany weddingCompany = new WeddingCompany(new You());
//        weddingCompany.HappyMarry();
    }

}
interface Marry{
    //人间四大喜事
      //久旱逢甘霖
      //他乡遇故知
      //洞房花烛夜
      //金榜题名时
    void HappyMarry();
}

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

    @Override
    public void HappyMarry() {
        System.out.println("你今天结婚了，开心吗");
    }
}

//代理对象，和帮助你结婚
class WeddingCompany implements Marry{

    //代理谁--》 真实目标角色
    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 after() {
        System.out.println("结婚之后，收尾款");
    }

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

4.线程的5种状态

4.1 线程的停止

package com.liang.state;

//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 TestStop implements  Runnable {
    //1.设置一个标识位
    private boolean flag = true;

    @Override
    public void run() {
        int i = 0;
        while (flag){
            System.out.println("run...Thread"+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) {

        TestStop testStop = new TestStop();
        new Thread(testStop).start();//启动线程


        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
                testStop.stop();
                System.out.println("线程该停止了");
            }
        }
    }
}

4.2 线程休眠

模拟网络延时: 放大问题的发生性

package com.liang.state;

import com.liang.demo01.TestThread4;

//模拟网络延时: 放大问题的发生性
public class TestSleep 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-- + "票");

        }
    }

    public static void main(String[] args) {

        TestSleep ticket = new TestSleep();

        new Thread(ticket,"小号").start();
        new Thread(ticket,"姐姐").start();
        new Thread(ticket,"康康").start();
    }
}

模拟倒计时

package com.liang.state;

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

//模拟倒计时，，
public class TestSleep2 {

    public static void main(String[] args) {
        //打印当前系统时间
        Date startTime = new Date(System.currentTimeMillis());//获得系统当前时间

        while (true){
            try {
                Thread.sleep(1000);
                System.out.println(new SimpleDateFormat("HH:mm:ss").format(startTime));
                startTime = new Date(System.currentTimeMillis());//更新当前时间
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }
//模拟倒计时
    public static void tenDown() throws InterruptedException {
        int num = 10;
        while (true){
            Thread.sleep(1000);
            System.out.println(num--);
            if (num<0){
                break;
            }
        }
    }
}

4.3 线程礼让

package com.liang.state;

//测试礼让线程
//礼让不一定成功，看cpu心情
public class TestYield {

    public static void main(String[] args) {
        MyYield myYield =  new MyYield();

        new Thread(myYield,"a").start();
        new Thread(myYield,"c").start();
    }

}

class MyYield implements Runnable{

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

    }
}

4.3 线程插入

package com.liang.state;

//测试join方法  想象插队
public class TestJoin implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("线程的vip来了"+i);
        }
    }

    public static void main(String[] args) throws InterruptedException {
        TestJoin testJoin = new TestJoin();
        Thread thread = new Thread(testJoin);
        thread.start();

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

4.4 线程状态

package com.liang.state;

//观察测试线程的状态
public class TestState {

    public static void main(String[] args) throws InterruptedException {

        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);//new

        //观察启动后

        thread.start();//启动线程
        state = thread.getState();
        System.out.println(state);//Run

        while (state!= Thread.State.TERMINATED){//只有线程不终止，就一直输出状态
            Thread.sleep(100);
            state = thread.getState();//更新线程
            System.out.println(state);//输出状态
        }
        //thread.start(); 死忙之后的线程不能在启动
        }
    }

4.5 线程的优先级

package com.liang.state;

//测试线程的优先级
public class TestPriority{

    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);
        Thread t4 = new Thread(myPriority);
        Thread t5 = new Thread(myPriority);
        Thread t6 = new Thread(myPriority);

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

        t2.setPriority(1);
        t2.start();

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

        t4.setPriority(Thread.MAX_PRIORITY);//=10
        t4.start();

        t5.setPriority(8);
        t5.start();

        t6.setPriority(5);
        t6.start();

        }
}

class MyPriority implements Runnable{

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

4.6 守护线程

package com.liang.state;
//测试守护线程
//上帝守护你
public class TestDaemon {

    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表示是用户线程，正常的线程都是用户线程。。

        thread.start();//上帝守护线程启动

        new Thread(you).start();//你  用户线程启动...
    }
}

//上帝
class God implements Runnable{
    @Override
    public void run() {
        while (true){
            System.out.println("上帝保护着你");
        }
    }
}


//你
class You implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("每天开开心心活着");
        }
        System.out.println("-===goodbye world====");
    }
}

5. 线程的同步

使用锁可能会引起性能倒置的问题

5.1 线程不安全测试 -银行同时取钱

package com.liang.syn;

import com.sun.org.apache.bcel.internal.generic.NEW;

//不安全的取钱
//两个人去银行取钱，账户
public class UnsafeBank {
    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 girlfriend = new Drawing(account, 100, "你女朋友");


        you.start();
        girlfriend.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;//添加构造方法
    }
}


//银行： 模拟取款
class Drawing extends Thread{
    Account account;//账户
    //取了多少钱哦
    int drawingMoney;
    //现在手里多少区别
    int NowMoney;

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

    }
    //取钱

    @Override
    public void run() {
        //判断有没有钱
        if (account.money-drawingMoney<0){
            System.out.println(Thread.currentThread().getName()+"没钱了，取不了");
            return;
        }
        //sleep可以放大问题的发生性
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //卡内余额 = 余额 - 你取得钱
        account.money = account.money-drawingMoney;
        //你手里的钱
        NowMoney = NowMoney + drawingMoney;

        System.out.println(account.name+"余额为："+account.money);
     //Thread.currentThread().getName() = this.getName()
        System.out.println(this.getName()+"手里的钱："+NowMoney);
    }
}

5.2 线程不安全测试 -同时买票

package com.liang.syn;

//不安全的买票
//线程不安全，有重票
public class UnsafeBuyTicket {

    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"kd").start();
        new Thread(station,"lbj").start();
        new Thread(station,"kb").start();
    }


}
class BuyTicket implements Runnable{
   //票
    private int ticketNums =10;
    boolean flag = true;//外部停止方式


    @Override
    public void run() {
        //买票
    while (flag){
    buy();
    }
    }

    private void buy(){
        //判断是否有票
        if (ticketNums<=0){
            flag = false;
            return;
        }
        //模拟延时
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //买票
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
    }
}

5.3 线程不安全测试 -ArrayList 集合

package com.liang.syn;

import java.util.ArrayList;
import java.util.List;
//线程不安全的集合
public class UnSafeList {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());//getName()获取线程的名字
            }).start();
        }
        try {
            Thread.sleep(30);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println(list.size());
    }
}

5.4 线程同步synchronized（隐式）

关键字：队列和锁

5.4.1 同步块（重要）

1. 在方法上面加上synchronized 同步方法 实现了一个锁，锁的是this，刚刚锁的是银行，所以没有用 ，还是负数
2. 同步块(可以锁任何对象) ，锁的对象就是变化的量，需要增删改的量

 1.上面的集合不安全
     new Thread(()->{
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
              //getName()获取线程的名字
            }).start();
        }

2.上面例子买票的不安全
    //在方法上面加上synchronized   同步方法 实现了一个锁，锁的是this
    private synchronized void buy(){
        //判断是否有票
        if (ticketNums<=0){
            flag = false;
            return;
        }
    
  3.上面例子银行取钱的不安全
      synchronized 默认锁的是this，刚刚锁的是银行，所以没有用 ，还是负数
    @Override
    public  void run() {
        synchronized (account){  //同步块(可以锁任何对象)  锁的对象
                                 //锁的对象就是变化的量，需要增删改的量

            //判断有没有钱
            if (account.money-drawingMoney<0){
                System.out.println(Thread.currentThread().getName()+"没钱了，取不了");
                return;
            }
            //sleep可以放大问题的发生性
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //卡内余额 = 余额 - 你取得钱
            account.money = account.money-drawingMoney;
            //你手里的钱
            NowMoney = NowMoney + drawingMoney;

            System.out.println(account.name+"余额为："+account.money);
            //Thread.currentThread().getName() = this.getName()
            System.out.println(this.getName()+"手里的钱："+NowMoney);
        }



    }

集合都加泛型，约束

5.5 线程安全CopyOnWriteArrayList 测试

package com.liang.demo01;

import java.util.concurrent.CopyOnWriteArrayList;

//测试juc安全类型的集合
public class TestJUC{
    public static void main(String[] args) {
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(() -> {
                list.add(Thread.currentThread().getName());
            }).start();
        }
            try {
                Thread.sleep(30);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }


            System.out.println(list.size());
        }

    }

6.死锁

package com.liang.demo01;

//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 DeadLock {

    public static void main(String[] args) {

        Makeup g1 = new Makeup(0,"灰姑凉");
        Makeup g2 = new Makeup(1,"baibai");


    g1.start();
    g2.start();
    }

}
//口红
class Lipstick{

}

//镜子
class Mirror{

}
class Makeup extends Thread{

    //需要的资源只有一份，用static来保证只有一份
 static Lipstick lipstick = new Lipstick();
 static Mirror mirror = new Mirror();

 int choice;//选择s
    String girlName;//使用化妆品的人

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


    @Override
    public void run() {

       //化妆

        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){//获得口红的锁
                System.out.println(this.girlName+"获得口红的锁");
                Thread.sleep(1000);


            }
            synchronized (mirror){//一秒钟后获得镜子
                System.out.println(this.girlName+"获得镜子的锁");
            }
        }else {
            synchronized (mirror){//获得镜子的锁
                System.out.println(this.girlName+"获得镜子的锁");
                Thread.sleep(2000);


            }
            synchronized (lipstick){//一秒钟后获得口红
                System.out.println(this.girlName+"获得口红的锁");
            }
        }
    }
}
把同步锁代码都拿出来，别同时方法就ok了
    

6.1 Lock（锁）显式

package com.liang.demo01;

import java.util.concurrent.locks.ReentrantLock;

public class TestLock  {
    public static void main(String[] args) {
        TestLock2 testLock2=new TestLock2();
        new Thread(testLock2,"刚个").start();
        new Thread(testLock2,"刚个").start();
        new Thread(testLock2,"刚个").start();
    }
}

class TestLock2 implements Runnable{
    int ticketNums = 10;

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

    @Override
    public void run() {
        while (true){

            try {
                lock.lock();//加锁
                if (ticketNums>0) {

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

                    System.out.println(ticketNums--);
                }else {
                    break;
                }
            }finally {
                //解锁
                lock.unlock();
            }

        }
    }
}

6.2 生产者和消费者

6.3 用wait等待，用notify来唤醒

package com.liang.gaoji;

//测试生产消费者问题2：信号灯法，标志位解决
public class TestPc2 {
    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){//构造方法
        this.tv=tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            if (1%2==0){
                this.tv.play("快乐大本营");
            }else {
                this.tv.play("抖音");
            }
        }
    }
}


//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 t
    //观众等待，演员表演 f

    String voice;     //表演的节目
    boolean flag = true;

    //表演
    public synchronized void play(String voice) {//只要涉及到并发就使用synchronized

        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("观看了："+voice);

        //通知演员表演
    this.notifyAll();
    this.flag=!this.flag;
    }
}

6.4 线程池

```java
package com.liang.gaoji;

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

//测试线程池
public class TestPool {

    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 service = Executors.newFixedThreadPool(10);

        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());

        //2.关闭连接
        service.shutdown();
    }

}

class MyThread implements Runnable{
    @Override
    public void run() {

            System.out.println(Thread.currentThread().getName());
        }

}

7. 多线程总结

package com.liang.gaoji;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

//回顾总结多线程的创建
public class ThreadNew {
    public static void main(String[] args) {
        new MyThread().start();//继承thread

        new Thread(new MyThread2()).start();//实现runnable

        FutureTask<Integer> futureTask = new FutureTask<Integer>(new MyThread3());//实现callable
        new Thread(futureTask).start();
        try {
            Integer integer = futureTask.get();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

    }

}

//1.继承Thread类
class MyThread extends Thread{
    @Override
    public void run() {
        System.out.println("MyThread1");
    }
}

//2.实现runnable接口
class MyThread2 implements Runnable{
    @Override
    public void run() {
        System.out.println("mythread2");
    }
}
//3.实现callable接口
class  MyThread3 implements Callable<Integer>{
    @Override
    public Integer call() throws Exception {
        System.out.println("MyThread3");
        return 100;
    }
}

8 Java中的sleep与wait区别

sleep
-让当前线程休眠指定时间。
-休眠时间的准确性依赖于系统时钟和CPU调度机制。
-不释放已获取的锁资源，如果sleep方法在同步上下文中调用，那么其他线程是无法进入到当前同步块或者同步方法中的。
-可通过调用interrupt()方法来唤醒休眠线程。

wait
-让当前线程进入等待状态，当别的其他线程调用notify()或者notifyAll()方法时，当前线程进入就绪状态
-wait方法必须在同步上下文中调用，例如：同步方法块或者同步方法中，这也就意味着如果你想要调用wait方法，前提是必须获取对象上的锁资源
-当wait方法调用时，当前线程将会释放已获取的对象锁资源，并进入等待队列，其他线程就可以尝试获取对象上的锁资源。

sleep vs wait

https://java2blog.com/difference-between-sleep-and-wait-in/