Core Java 面试题与答案

问题 241. What is the purpose of the File class?

The File class is used to create objects that provide access to the files and directories of a local file system.

问题 242. What is a socket?

A socket is an endpoint for communication between two machines.

问题 243. How do I convert a numeric IP address like 192.18.97.39 into a hostname like java.sun.com?

String hostname = InetAddress.getByName("192.18.97.39").getHostName();

问题 244. How can my application get to know when a HttpSession is removed?

Define a Class HttpSessionNotifier which implements HttpSessionBindingListener and implement the functionality what you need in valueUnbound() method. Create an instance of that class and put that instance in HttpSession.

问题 245. How will you invoke any external process in Java?

Runtime.getRuntime().exec('.)