JAVA API文档是JAVA的应用编程接口，目的是提供应用程序与开发人员基于某软件或硬件的以访问一组例程的能力，而又无需访问源码，或理解内部工作机制的细节。如果开发人员对正在使用的类不熟悉，想查看类里面的变量或者方法，就可以打开Java API文档进行阅读和查看，从而让开发人员迅速地提高能力。(JAVA API document is JAVA application programming interface, the purpose is to provide the application and development of personnel based on a hardware or software to access a set of routines, without access to the source code, or understand the details of the internal working mechanism. If developers are unfamiliar with the classes that are being used, and want to see the variables or methods within the class, you can open the Java API document to read and see, allowing developers to quickly improve their capabilities.)