本文主要是介绍Java自学-多线程(3)，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

Java自学-多线程(3)

1、线程的优先级

package lesson04;

/**
 * Author: Gu Jiakai
 * Date: 2021/8/12 14:50
 * FileName: TestPriority
 * Description:
 */
//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，再启动。
        t1.start();

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

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

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

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

        t6.setPriority(7);
        t6.start();

    }
}

class Mypriority implements Runnable{

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

2、守护线程

package lesson04;

/**
 * Author: Gu Jiakai
 * Date: 2021/8/12 15:11
 * FileName: TestDaemon
 * Description:
 */
//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("God Bless You!");
        }
    }
}

//你
class You implements Runnable{

    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("你一生都开心地活着！");
        }
        System.out.println("======GoodBye,World!======");
    }
}

3、线程同步机制

4、三大不安全案例

...

5、同步方法及同步块

package synchronized_test;

/**
 * Author: Gu Jiakai
 * Date: 2021/8/12 16:10
 * FileName: UnsafeBuyTicket
 * Description:
 */
//不安全的买票
//线程不安全,有负数
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();

        new Thread(buyTicket,"我").start();
        new Thread(buyTicket,"蔡伟").start();
        new Thread(buyTicket,"黄牛党").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();
            }
    }

    //synchronized 同步方法，锁的是this。
    private synchronized 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--);
    }
}

package synchronized_test;

/**
 * Author: Gu Jiakai
 * Date: 2021/8/12 16:25
 * FileName: UnsafeBank
 * Description:
 */
//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(1000,"结婚基金");

        WithDrawing you = new WithDrawing(account,50,"蔡伟");
        WithDrawing girlfriend = new WithDrawing(account,100,"蔡伟女友");

        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;
    }
}

class WithDrawing extends Thread{
    Account account;//账户
    //取了多少钱
    int withdraw_money;
    //现在手里有多少钱
    int now_money;

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

    //取钱
    //synchronized 默认锁的是this
    @Override
    public void run() {
        //锁的对象就是变化的量，,需要增删改的对象
        synchronized (account){
            //判断有没有钱
            if(account.money-withdraw_money<0){
                System.out.println(Thread.currentThread().getName()+"钱不够，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-你要取的钱
            account.money=account.money-withdraw_money;
            //你手里的钱
            now_money=now_money+withdraw_money;

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

package synchronized_test;

import java.util.ArrayList;

/**
 * Author: Gu Jiakai
 * Date: 2021/8/12 16:59
 * FileName: UnsafeList
 * Description:
 */
//线程不安全的集合
public class UnsafeList {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

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

    }
}

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