神奇的AtomicInteger

• 当AtomicInteger的值为最大值2147483647时，执行incrementAndGet()会发生什么？
• 当AtomicInteger的值为最小值-2147483648时，执行decrementAndGet()会发生什么？

        AtomicInteger max = new AtomicInteger(Integer.MAX_VALUE);
        System.out.println(max);
        System.out.println(max.incrementAndGet());
        System.out.println("--------------------");
        AtomicInteger min = new AtomicInteger(Integer.MIN_VALUE);
        System.out.println(min);
        System.out.println(min.decrementAndGet());

测试结果如下：

2147483647
-2147483648
--------------------
-2147483648
2147483647

有时候并不能符合我们的业务场景，比如队列消息从0开始增加，当增加到最大值时我们不希望下一个值为负数。而是从0开始，周而复始，对incrementAndGet和decrementAndGet分别做如下改造：

private final AtomicInteger i;
public final int incrementAndGet() {
        int current;
        int next;
        do {
            current = this.i.get();
            next = current >= 2147483647?0:current + 1;
        } while(!this.i.compareAndSet(current, next));

        return next;
    }

    public final int decrementAndGet() {
        int current;
        int next;
        do {
            current = this.i.get();
            next = current <= 0?2147483647:current - 1;
        } while(!this.i.compareAndSet(current, next));

        return next;
    }