synchronized修改三大不安全案例

synchronized 同步方法，锁的是this

package com.guo.syn;

//不安全买票
//线程不安全，有负数
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"美丽的李悦").start();
        new Thread(station,"帅气的陈果").start();
        new Thread(station,"操蛋的黄牛").start();
    }
}


class BuyTicket implements Runnable{

    //票
    private int ticketNums = 100;
    boolean flag = true; //外部停止方式
    @Override
    public void run() {
        //买票
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }

    }
    //synchronized 同步方法，锁的是this
    private synchronized void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums<=0){
            flag = false;
            return;
        }

        //模拟延时
            Thread.sleep(100);


        //买票
        System.out.println(Thread.currentThread().getName()+"-->买到了第"+ticketNums--+"张票");
    }

}

同步块_锁住账户 synchronized (account){}

package com.guo.syn;

//不安全的取钱
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(150,"结婚基金");

        Drawing liyue = new Drawing(account,100,"李悦");
        Drawing chenguo = new Drawing(account,50,"陈果");

        chenguo.start();
        liyue.start();

    }
}

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

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

//银行
class Drawing extends Thread{
    Account account;//账户
    //取了多少钱
     int drawingMoney;
    //现在手里有多少钱
    int nowMoney;


    public Drawing(Account account,int drawingMoney,String name){

        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;

    }
    //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-drawingMoney<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) {
                throw new RuntimeException(e);
            }

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

            System.out.println(account.name+"余额为："+account.money);

            System.out.println(this.getName()+"手里的钱："+nowMoney);

        }

    }
}

同步块

package com.guo.syn;

import java.sql.Array;
import java.util.ArrayList;

public class UnsafeList {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

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

    }
}