public class AtomicReferenceDemo {

    public static void main(String[] args) {

        User cuzz = new User("cuzz", 18);

        User faker = new User("faker", 20);

        AtomicReference<User> atomicReference = new AtomicReference<>();

        atomicReference.set(cuzz);

        System.out.println(atomicReference.compareAndSet(cuzz, faker)); // true

        System.out.println(atomicReference.get()); // User(userName=faker, age=20)

    }

}

/**

 * 当有一个值从 A 改为 B 又改为 A，这就是 ABA 问题

 **/

public class ABADemo {

    private static AtomicReference<Integer> atomicReference = new AtomicReference<>(100);

    public static void main(String[] args) {

        new Thread(() -> {

            atomicReference.compareAndSet(100, 101);

            atomicReference.compareAndSet(101, 100);

        }).start();

        new Thread(() -> {

            // 保证上面线程先执行

            try {

                Thread.sleep(1000);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            atomicReference.compareAndSet(100, 2019);

            System.out.println(atomicReference.get()); // 2019

        }).start();

    }

}

/**

 * 我们先保证两个线程的初始版本为一致，后面修改是由于版本不一样就会修改失败

 **/

public class ABADemo2 {

    private static AtomicStampedReference<Integer> atomicStampedReference = new AtomicStampedReference<>(100, 1);

    public static void main(String[] args) {

        new Thread(() -> {

            int stamp = atomicStampedReference.getStamp();

            System.out.println(Thread.currentThread().getName() + " 的版本号为：" + stamp);

            try {

                Thread.sleep(1000);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            atomicStampedReference.compareAndSet(100, 101, atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1 );

            atomicStampedReference.compareAndSet(101, 100, atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1 );

        }).start();

        new Thread(() -> {

            int stamp = atomicStampedReference.getStamp();

            System.out.println(Thread.currentThread().getName() + " 的版本号为：" + stamp);

            try {

                Thread.sleep(3000);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            boolean b = atomicStampedReference.compareAndSet(100, 2019, stamp, stamp + 1);

            System.out.println(b); // false

            System.out.println(atomicStampedReference.getReference()); // 100

        }).start();

    }

}