public class ABADemo {
    public static void main(String[] args) {
        User z = new User("z3", 22);
        User li = new User("li", 24);

        AtomicReference<User> atomicReference = new AtomicReference<>();
        atomicReference.set(z);

        System.out.println(atomicReference.compareAndSet(z, li) + "\\t " + atomicReference.get().getUserName());
        System.out.println(atomicReference.compareAndSet(z, li) + "\\t " + atomicReference.get().getUserName());
    }
}

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

    String userName;
    int age;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public int getAge() {
        return age;
    }

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