JAVA instanceof 怎么回事儿

java的instanceof操作符行为很是古怪啊      似乎instanceof前面确定了后面就是受限的，只能是接口或前面对象的类的类继承链中的一员（是为了提高性能吗，还是一个bug就），而后面固定的情况下（下面代码中的isMyType方法）前面的对象可以是任何类型的（包括null虽然它总会得到FALSE）。      

可惜Class.isInstance（）也是个native方法，真愁人啊可。   

有人了解不这个？

 

public class InstanceofTest  implements IA{
    public static void main(String[] args){
        SubClass sc = new SubClass();
        InstanceofTest it = new InstanceofTest();
//        提示 Inconvertible types:cannot cast 'SubClass' to 'AnoSubClass'
//        System.out.printf("sc instanceof AnoSubClass:%b%n", sc instanceof AnoSubClass);
        System.out.printf("it instanceof SubClass:%b%n", it instanceof SubClass);
        System.out.printf("sc instanceof IA:%b%n", sc instanceof IA);
        System.out.printf("sc instanceof IB:%b%n", sc instanceof IB);
        //insstanceof前面不能用int，这里不会发生自动装箱
        System.out.println(new Integer(2) instanceof Integer);
        sc.test();
        System.out.println(it.isMyType(new Integer(2)));
//        System.out.printf("new Integer(2) instanceof InstanceofTest:%b%n", new Integer(2) instanceof InstanceofTest);
    }

    <T> boolean isMyType(T t){
         return t instanceof InstanceofTest;
    }
}

    interface IA {}
    interface IB{}
    class AnoSubClass extends InstanceofTest{}
    class SubClass extends InstanceofTest{
        void test()
        {
            System.out.println("#####this is SubClass");
            System.out.printf("#####this instanceof SubClass:%b%n",this instanceof SubClass);
            System.out.printf("#####IA.class.isInstance(this):%b%n",IA.class.isInstance(this));
            System.out.printf("#####super.getClass().isInstance(this):%b%n",super.getClass().isInstance(this));
            System.out.printf("#####this instanceof InstanceofTest:%b%n",this instanceof InstanceofTest);
            System.out.printf("#####AnoSubClass.class.isInstance(this):%b%n",AnoSubClass.class.isInstance(this));
//            System.out.printf("#####this instanceof Object:%b",this instanceof AnoSubClass);
        }
    }