Thread safety issues

Thread safety issues refer to ： When multiple threads operate a shared resource at the same time , Business security issues may arise ,

It usually happens when you modify the same shared resource with your colleagues .

Let me give you an example of this code ：

The first is this shared account class People, It contains updateMoney（） Method , Used to modify the amount stored inside Money,

public class People {
    private double money;

    public People() {
    }

    public People(double money) {
        this.money = money;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }
    public void updateMoney(double price){
        System.out.println(" The current thread has connected to the account , The account balance ："+money);
        System.out.println(Thread.currentThread().getName()+" Withdraw money ："+price);
        money-=price;
        System.out.println(" The account balance ："+money);
    }
}

The second is its main class ;

public class Test1 {
    public static void main(String[] args) throws Exception {
        People people=new People(1000.0);// Put... In your account 1000 element 
        // Create two threads 
        new MyThread(people,"1 Number ").start();
        new MyThread(people,"2 Number ").start();
    }
}
class MyThread extends Thread{
    private People people;
    public MyThread(People people,String name) {
        super(name);
        this.people=people;
    }

    @Override
    public void run(){
        // call People Methods , Take it out of it 1000 element ;
        people.updateMoney(1000.0);
    }
}

Of course , There's a problem , The two threads created execute simultaneously , They will simultaneously move from People Remove from 1000 element , And originally People There is only 1000 element ,name Will result in the following results ;

The current thread has connected to the account , The account balance ：1000.0
The current thread has connected to the account , The account balance ：1000.0
2 No. to withdraw money ：1000.0
1 No. to withdraw money ：1000.0
The account balance ：0.0
The account balance ：-1000.0
 

This causes thread safety problems