线程的三种不安全问题

线程的三种不安全问题

问题一：买票问题

package Unsafe;

public class Unsafebuyt {
    
    
    public static void main(String[] args) {
    
    
        Unsafe unsafe=new Unsafe();
        new Thread(unsafe,"小明").start();//开启线程
        new Thread(unsafe,"小红").start();
        new Thread(unsafe,"小兰").start();
    }
}
class Unsafe implements Runnable{
    
    
    boolean flag=true;
    //票
    private int ticket=10;
    @Override
    //买票
    public void run() {
    
    
        while (flag){
    
    //当标志位是true的时候执行，当变为false时停止方法
        buy();}
    }
    //怎么买
    private void buy(){
    
    
            if(ticket<=0){
    
    //如果票没了，标志位变为false
                flag=false;
                return;//跳出方法
            }
            //模拟延时
            try {
    
    
                Thread.sleep(100);
            } catch (InterruptedException e) {
    
    
                e.printStackTrace();
            }

            System.out.println(Thread.currentThread().getName()+"---->"+ticket--);

    }
}

解决办法

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问题二：取钱问题

package Unsafe;

/**
 * 账户
 * 银行
 */
public class Unbank {
    
    
    public static void main(String[] args) {
    
    
        Account account = new Account(100,"你的钱");//规定账户名字和卡内余额
        Bank girlfriend = new Bank(account,100,"girlfriend");//模拟一个线程
        Bank bank = new Bank(account,50,"你");//模拟一个线程
        girlfriend.start();//开启线程
        bank.start();
    }
}
//银行卡账户 有钱和名字
class Account {
    
    
    int money;
    String name;
    public Account( int money, String name) {
    
    //用构造器获取这个名字
        this.money=money;
        this.name = name;
    }
}
//银行 有账户、账户余额；
class Bank extends Thread{
    
    
    Account account;//账户
    int nowmoney;//手里的钱
    int movemoney;//要取走的钱

    public Bank(Account account, int movemoney, String name) {
    
    
        super(name);//super写在首行 调用父类的名字==就是线程的名字（自己规定）
        this.account= account;//获取账户
        this.movemoney = movemoney;//账户要取走的钱
    }

    @Override
    public void run() {
    
    //开始取钱过程 银行要做的事
    if(account.money-movemoney<=0){
    
    //账户余额<要取走的钱
        System.out.println(Thread.currentThread().getName()+"卡内余额不足");
        return;//跳出方法
    }
        try {
    
    //模拟延时，因为要最少两个人取钱
            Thread.sleep(1000);
        } catch (InterruptedException e) {
    
    
            e.printStackTrace();
        }
        System.out.println(account.name+"卡内余额"+account.money);
        account.money=account.money-movemoney;//更新卡内余额
        nowmoney=nowmoney+movemoney;//更新手里的钱
        System.out.println(getName()+"取走的钱"+nowmoney);
        System.out.println(account.name+"卡内余额"+account.money);
    }
}

解决办法

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问题三：线程内不安全集合问题

package Unsafe;

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

public class UnsafeList {
    
    
    public static void main(String[] args) {
    
    
        List<String> list =new ArrayList<String>();//新建数组集合
        for (int i = 0; i <= 10000; i++) {
    
    //循环开启10000个线程
            new Thread(()->//lambda表达式
                   list.add(Thread.currentThread().getName())//把线程加到list里
                    ).start();//开启线程
        }
        //模拟延时
        try {
    
    
            Thread.sleep(5000);
        } catch (InterruptedException e) {
    
    
        }
        //输出集合大小
        System.out.println(list.size());
    }

}

解决办法
或者可用JUC并发编程

package Unsafe;

import java.util.concurrent.CopyOnWriteArrayList;

public class TestJuc {
    
    
    public static void main(String[] args) {
    
    
        CopyOnWriteArrayList<String> list=new CopyOnWriteArrayList<>();
        for (int i = 0; i < 10000; i++) {
    
    //循环开启10000个线程
            new Thread(()->{
    
    //lambda表达式
                    list.add(Thread.currentThread().getName());//把线程加到list里
            }).start();//开启线程
        }
        //模拟延时
        try {
    
    
            Thread.sleep(3000);
        } catch (InterruptedException e) {
    
    
        }
        //输出集合大小
        System.out.println(list.size());
    }
}

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xinyue Day3