This is because B is not in the classpath of the system class loader or its parent or ancestor class loaders.

这是因为 B 不在系统类装入器或者它的双亲或祖先类装入器的类路径中。

youdao

The following code will stub the system class Date to always return the same date, say Ground Hog Day, as in Listing 6.

下面的代码对系统类 Date 进行 stub 以便总是返回相同的日期，比如 Ground Hog Day，如清单 6 所示。

youdao

Here, we use reflection because we have loaded the application using a class loader that is not the system class loader.

这里，我们使用反射的原因是因为我们已经使用非系统类加载器加载了应用程序。

youdao

President Obama said the current system has led the country to a breaking point, imposing hardships on middle-class Americans who struggle to pay for health care, who are unable to obtain it.

VOA: standard.2009.09.10

Because it challenged the whole class system, that people are born into a certain place and cannot-- and should not-- be moved.

因为它挑战了整个阶级体系，人生来就有阶级，不能-,也不应该被改变。

哈佛公开课 - 幸福课课程节选

I think that there's definitely a class system, but I also feel like everyone is very accessible,

我觉得，毫无疑问，这是种阶层系统，但我也感觉何种人都很容易接触到。

美国贫富差距？ - SpeakingMax英语口语达人

"However, it turns out that the fix was not complete as one can still abuse invokeWithArguments method to setup calls to invokeExact method with a trusted system class as a target method caller, " Gowdiak wrote.

CNN: STORY HIGHLIGHTS

Interestingly, even as Thatcher was working to open things up and making the British class system more like America's, the US class system started becoming more and more rigid.

BBC: Class calculator: A US view of the class system

However, because some character classes or skill sets can easily defeat characters of other classes or skills in many MMORPGs, developers should consider a skill-point character development system over a class-based system to balance play and to provide an opportunity for any character class engaged in combat to win.

FORBES: Studying Player Commitment To MMORPGs