单例模式的懒汉模式为什么在高并发中会出现问题？一个代码例子告诉你

import lombok.Data;

import java.util.concurrent.atomic.AtomicInteger;

@Data
public class Phone {

    //手机余额
    private AtomicInteger count = new AtomicInteger(3);

    private Phone(){}

    private static Phone phone;

    public static Phone getInstance(){
        if (phone == null){
            phone = new Phone();
        }
        return phone;
    }

    public int getReduce(){
        return count.decrementAndGet();
    }

}

public class BingFa {

    public static void main(String[] args) {

        // 创建3个线程，线程里面进行加操作
        for (int i = 0; i < 3; i++) {
            new Thread(() -> {
                Phone phone = Phone.getInstance();
                int reduce = phone.getReduce();
                System.out.println(Thread.currentThread().getName()+
                					"线程抢到了手机，剩余手机数量"+"-----"+reduce);
            }, String.valueOf(i)).start();
        }

    }
}