CAS你知道吗？原子类AtomicInteger的ABA问题谈谈？

（1）CAS是什么？

       比较并交换

     举例1,  CAS产生场景代码？

import java.util.concurrent.atomic.AtomicInteger;

public class CASDemo {
    public static void main(String[] args) {
        AtomicInteger atomicInteger=new AtomicInteger(5);//主物理内存
        //比较5
        System.out.println(atomicInteger.compareAndSet(5, 2019)+"\t current data（主物理内存） : "+ atomicInteger.get());
        //修改失败
        System.out.println(atomicInteger.compareAndSet(5, 1024)+"\t current data（主物理内存） : "+ atomicInteger.get());
    }
}

   举例2,  CAS产生场景代码？原子引用

public class CAS_ABADemo {
    public static void main(String[] args) {

        //========================原子引用==========================
        User A = new User("A", 123);
        User B = new User("B", 456);
        //主物理内存 引用比较的是地址
        AtomicReference<User> atomicReference1 = new AtomicReference<>();
        atomicReference1.set(A);
        System.out.println(atomicReference1.compareAndSet(A, B) + "\t" + atomicReference1.get().toString());
        System.out.println(atomicReference1.compareAndSet(A, B) + "\t" + atomicReference1.get().toString());
    }
}
class User {
    String name;
    int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public User() {
    }

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

原子引用