static public IServiceManager asInterface(IBinder obj) {
        // obj为BinderProxy对象
        if (obj == null) {
            return null;
        }
        // BinderProxy对象的该方法默认返回null
        IServiceManager in = (IServiceManager)obj.queryLocalInterface(descriptor);
        if (in != null) {
            return in;
        }
        return new ServiceManagerProxy(obj);
}

由上述代码可知ServiceManagerNative.asInterface(new BinderProxy()) 等价于new ServiceManagerProxy(new BinderProxy())。