多线程：通过两个不安全例子学习同步锁，synchronized同步方法/同步块，JUC, lock锁

模拟抢购火车票

package com.cl.syn;

//不安全买票，会出现多人买同一张票，导致票数出现负数
//解决，synchronized，同步方法，让多个线程之间做到排队等待
//缺点：若将一个大的方法申明synchronized将会影响效率

public class UnsafeBuyTicket {

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

        new Thread(station,"帅气的我").start();
        new Thread(station,"老黄牛").start();
        new Thread(station,"小黄").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 synchronized void buy(){
        //判断是否有票
        if (ticketNums<=0){
            flag=false;
            return;
        }
        //模拟延时,放大存在问题
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //那个进程抢到票
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
    }
}

模拟多人在统一账户取钱

package com.cl.syn;

//不安全的取钱
//模拟两个人去银行取钱，账户
//解决：
//synchronized默认同步的是this，本身
//因此要用同步块，

public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(1000, "结婚基金");

        Drawing you=new Drawing(account,50,"你");
        Drawing friend=new Drawing(account,100,"friend");

        you.start();
        friend.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;//账户
    int drawingMoney;//取了多少钱
    int nowMoney;//手里有多少钱

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

    }

    //取钱

    @Override
    public void run() {

        //锁的对象就是变化的量，需要增删改查的对象
        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(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

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

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

}

测试JUC安全类型的集合

package com.cl.syn;

//util.concurrent，并发包
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(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

了解lock锁

package com.cl.syn;

import java.util.concurrent.locks.ReentrantLock;

//测试lock锁,加锁：lock.lock()
//          解锁：lock.unlock();
public class TestLock {
    public static void main(String[] args) {
        TestLock2 testLock2 = new TestLock2();

        new Thread(testLock2).start();
        new Thread(testLock2).start();
        new Thread(testLock2).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();
            }

        }
    }
}