使用Unsafe的时候遇到的小问题

在使用Unsafe.compareAndSwapLong时遇到了一点小问题,一不小心就出错

public class UnsafeDemo02 {

    private static Unsafe unsafe;

    public static void main(String[] args) throws Exception{
        Field unsafeField = Unsafe.class.getDeclaredField("theUnsafe");
        unsafeField.setAccessible(true);
        unsafe = (Unsafe)unsafeField.get(null);


        Field valueField = SonUnsafeDemo02.class.getDeclaredField("value");
        long valueOffset = unsafe.objectFieldOffset(valueField);

        SonUnsafeDemo02 son = new SonUnsafeDemo02();
        System.out.println(valueField.get(son));

        boolean b = unsafe.compareAndSwapLong(son, valueOffset, 5, 6);

        System.out.println(b);
        System.out.println(valueField.get(son));

    }

}

class SonUnsafeDemo02 {
    public long value = 5;
}

此时可以看到输出结果为:

5
true

6

但是如果改成如下这样

class SonUnsafeDemo02 {
//    public long value = 5L;
    public Long value = 5L;
}

此时的输出结果为

5 

false

5

对应于Unsafe.compareAndSwapInt方法测试也是一样的效果

总结: 对象的属性不能是包装类型,只能是基本数据类型,否则有可能报错

(小白日志)