private static final Unsafe unsafe = Unsafe.getUnsafe();//Unsafe所有并发工具的基础工具类
private static final long valueOffset; //成员变量value在当前AtomicReference对象中的地址偏移量
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static {
    try {//使用objectFieldOffset获取偏移量
        valueOffset = unsafe.objectFieldOffset
            (AtomicReference.class.getDeclaredField("value"));
    } catch (Exception ex) { throw new Error(ex); }
}
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private volatile V value;//value表示我们要修改/更新的目标对象

public AtomicReference(V initialValue) {
    value = initialValue;
}
public AtomicReference() {
}
public final void set(V newValue) {
    value = newValue;
}

    public final V get() {
        return value;
    }
    //最终设定 (延迟化设值，不保证新值newValue被所有立即可见)
    public final void lazySet(V newValue) {
        unsafe.putOrderedObject(this, valueOffset, newValue);
    }
    // CAS更新，（若expect==value,就将value设为update）并返回是否更新成功的布尔值
    public final boolean compareAndSet(V expect, V update) {
        return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
    }
    //同上的CAS,(方法定义上是对引用做弱比较，但实现细节和上面的compareAndSet相同)
    public final boolean weakCompareAndSet(V expect, V update) {
        return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
    }
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    //设置新值并返回旧值
    public final V getAndSet(V newValue) {
        return (V)unsafe.getAndSetObject(this, valueOffset, newValue);
    }
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    //Unsafe的getAndSetObject
    public final Object getAndSetObject(Object o, long offset, Object newValue) {
        Object v;
        do {
            v = getObjectVolatile(o, offset); //获取当前的值
        } while (!compareAndSwapObject(o, offset, v, newValue));//CAS更新
        return v;
    }

public final V getAndUpdate(UnaryOperator<V> updateFunction) {
    V prev, next;
    do {
        prev = get();//获取当前的value
        next = updateFunction.apply(prev); //updateFunction根据输入参数prev得到value新值
    } while (!compareAndSet(prev, next));//CAS更新
    return prev;
}
public final V updateAndGet(UnaryOperator<V> updateFunction) {
    V prev, next;
    do {
        prev = get();
        next = updateFunction.apply(prev);
    } while (!compareAndSet(prev, next));
    return next;
}
public final V getAndAccumulate(V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get();//获取当前的value
        next = accumulatorFunction.apply(prev, x);//accumulatorFunction根据输入参数prev、x两者得到value新值
    } while (!compareAndSet(prev, next));//CAS更新
    return prev;
}
public final V accumulateAndGet(V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get();
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSet(prev, next));
    return next;
}

public class AtomicRef {
    static class ID {
        private long serialNum;
        private String algo;
        private Date created;
        public ID(long serialNum, String algo, Date created) {
            this.serialNum = serialNum;
            this.algo = algo;
            this.created = created;
        }
　　//getter/setter省略
    }
    public static void main(String[] args) {
        AtomicReference<ID> idAtomicRef = new AtomicReference<>();
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        ID id1 = new ID(1248L, "random", new Date());
        ID id2 = new ID(3456L, "random", new Date());
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        idAtomicRef.set(id1);
        Boolean flag = idAtomicRef.compareAndSet(id1, id2);
        System.out.printf("CAS successful? %s,current ID:%s\n", flag, idAtomicRef);
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        id1.setCreated(new Date(System.currentTimeMillis() +3600*1000));
        flag= idAtomicRef.compareAndSet(id2, id1);
        System.out.printf("CAS successful? %s,current ID:%s\n", flag, idAtomicRef);
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        System.out.println(idAtomicRef);
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        ID id3 = new ID(1024L, "Random", new Date());
        idAtomicRef.set(id3);
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        ID id4 = idAtomicRef.updateAndGet(id -> new ID(id.getSerialNum() * 10, "scale", new Date()));
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        ID id5 = idAtomicRef.accumulateAndGet(id1, (x, y) -> {
            long serialNum = x.serialNum + y.serialNum;
            long time = (x.getCreated().getTime() + y.getCreated().getTime()) / 2;
            return new ID(serialNum, "accumulate", new Date(time));
        });
        System.out.println(id4);
        System.out.println(id5);
    }
}