The Security Manager
- 定义
官方：
A security manager is an object that defines a security policy for an application. This policy specifies actions that are unsafe or sensitive. Any actions not allowed by the security policy cause a SecurityException to be thrown. An application can also query its security manager to discover which actions are allowed.
理解：
它是一个应用的安全策略。这个策略指定当前的动作是安全or不安全or敏感。
- 示例
官方：
Typically, a web applet runs with a security manager provided by the browser or Java Web Start plugin. Other kinds of applications normally run without a security manager, unless the application itself defines one. If no security manager is present, the application has no security policy and acts without restrictions.
理解：
web 程序中的安全管理类是由浏览器或者启动插件提供的。其他应用程序通常没有安全管理类，除非我们自己去定义。
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