Java 多线程（七）三大不安全案例

一，买票

//不安全买票
public class UnsafeBuyTickets {
    public static void main(String[] args) {
        BuyTickets buyTickets = new BuyTickets();
        new Thread(buyTickets,"黄牛").start();
        new Thread(buyTickets,"平民").start();
        new Thread(buyTickets,"贵族").start();
        new Thread(buyTickets,"皇室").start();
    }
}

class BuyTickets implements Runnable{
    private int ticketsNum = 100;
    @Override
    public void run() {
        while(true){
            if (ticketsNum <=0){
                break;
            }
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"拿到了第"+ticketsNum--+"张票！");
        }
    }
}

结果会看到负数：

二，取钱

//不安全取钱
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100, "结婚基金");
        Draw you = new Draw(account,50,"你");
        Draw girlFriend = new Draw(account,100,"girlFriend");
        you.start();
        girlFriend.start();
    }
}

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

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}
//取钱
class Draw extends Thread{
    Account account;//账户
    int drawingMoney;//取多少钱
    int nowMoney;//手里多少钱

    public Draw(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()+"余额不足");
            return;
        }
        //sleep
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //卡内余额=卡里余额-取出钱
        account.money = account.money-drawingMoney;
        //手里钱=手里钱+取出钱
        nowMoney = nowMoney+drawingMoney;
        System.out.println(account.name+"余额为："+account.money);
        //Thread.currentThread().getName()等价于this.getName()
        System.out.println(this.getName()+"手里的钱:"+nowMoney);
    }
}

结果看到负数：

三，不安全集合

//线程不安全的集合
public class UnsafeList {
    public static void main(String[] args) throws InterruptedException {
        List<String> list = new ArrayList<String>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            }).start();
        }
        Thread.sleep(3000);
        System.out.println(list.size());
    }
}

结果看到集合中数量不够应该是有10000个：