執行緒三大不安全案例

• 買票

//不安全的買票
//執行緒不安全，有負數
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();


        new Thread(station,"苦逼的我").start();
        new Thread(station,"牛逼的你們").start();
        new Thread(station,"可惡的黃牛黨").start();
    }

}

class BuyTicket implements Runnable{

    //票
    private int ticketNums = 10;
    boolean flag = true; //外部停止方式

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

    private void buy() throws InterruptedException {
        //判斷是否有票
        if(ticketNums<=0){
            flag = false;
            return;
        }
        //模擬延時
        Thread.sleep(100);

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

• 銀行取錢

//不安全的取錢
//兩個人去銀行取錢，賬戶
public class UnsafeBank {
    public static void main(String[] args) {
        //賬戶
        Account account = new Account(100,"結婚基金");

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

        you.start();
        girlFriend.start();
    }
}

//賬戶
class Account{
    int money; //餘額
    String name; //卡名

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

//銀行：模擬取款
class Drawing extends Thread{

    Account account; //賬戶
    //取了多少錢
    int drawingMoney;
    //現在手裡有多少錢
    int nowMoney;

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


    }

    //取錢

    @Override
    public void run() {
        //判斷有沒有錢
        if (account.money-drawingMoney<0){
            System.out.println(Thread.currentThread().getName()+"錢不夠，取不了");
            return;
        }

        //sleep可以放大問題的發生性
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //卡內餘額 = 餘額 - 你取的錢
        account.money = account.money - drawingMoney;
        //你手裡的錢
        nowMoney = nowMoney + drawingMoney;

        System.out.println(account.name+"餘額為:"+account.money);
        //getName()+Thread.currentThread().getName() = this.getName()
        System.out.println(this.getName()+"手裡的錢："+nowMoney);
    }
}
 

• 執行緒不安全的集合

import java.util.ArrayList;
import java.util.List;

//執行緒不安全的集合
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());
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}