问题 单项选择题

关于Applet执行的操作,下面说法正确的是( )。

A.在运行时调用其他程序

B.可以进行文件读写操作

C.不能装载动态连接库和调用任何本地方法

D.试图,打开一个socket进行网络通信,但是所连接的主机并不是提供Applet的主机

答案

参考答案:C

解析: 本题考查Applet的概念。Java虚拟机为Applet提供能够良好运行的沙箱,一旦它们试图离开沙箱则会被禁止。由于Applet是通过网络传递的,这就不可避免地使入想到会发生安全问题。例如,有人编写恶意程序通过小应用程序读取用户密码并散播到网络上,这将会是一件非常可怕的事情。所以,必须对小应用程序进行限制。浏览器禁止Applet执行下列操作:Applet不能运行任何本地可运行程序,选项A错误。禁止加载本地库或方法,Applet只能使用自身的代码或Applet浏览器提供的JavaAPI,不允许装载动态连接库和调用任何本地方法,选项c正确。禁止读写本地计算机的文件系统,选项B错误,禁止向提供Applet之外的任何主机建立网络连接,如果Applet试图打开一个socket进行网络通信,所连接的主机必须是提供 Aoolet的主机,选项D错误。

单项选择题


Smallpox was the first widespread disease to be eliminated by human intervention. A highly contagious viral disease, it was endemic in Europe, causing the death of millions of people until the development of vaccination by Edward Jenner around 1800. In many non- European nations, it remained a dreaded, often fatal illness until very recently.
In May 1966, the World Health Organization (WHO), an agency of the United Nations, was authorized to initiate a global campaign to eradicate smallpox. The goal was to eliminate the disease in one decade. At the time, the disease posed a serious threat to people in thirty nations. More than 700 physicians, nurses, scientists, and other personnel from WHO joined about 200,000 health workers in the infected nations to battle the disease. Because similar projects for malaria and yellow fever had failed, few believed that smallpox could actually be eradicated, but eleven years after the initial organization of the campaign, no cases were reported in the field.
The strategy was not only to provide mass vaccinations but also to isolate patients with active smallpox in order to contain the spread of the disease and to break the chain of human transmission. Rewards for reporting smallpox assisted in motivating the public to aid health workers. One by one, each smallpox victim was sought out, removed from contact with others and treated. At the same time, the entire village where the victim had lived was vaccinated.
By April 1978, WHO officials announced that they had isolated the last known case of the disease, but health workers continued to search for new cases for two additional years to be completely sure. In May 1980, a formal statement was made to the global community. Today smallpox is no longer a threat to humanity. Routine vaccinations have been stopped worldwide.

Which of the following statements does NOT refer to smallpox

A.Previous projects had failed.

B.People are no longer vaccinated for it.

C.The World Health Organization mounted a worldwide campaign to eradicate the disease.

D.It was a serious threat.

单项选择题