in-memory file system

note, don't talk about performance, scalability before you complete the basic features.

main functionality

• files , directory, a directory may contains files or sub directory
• metadata of file / directory: name, creation time, access time, j...
• a file system can be modeled as a tree consisting of files / subdirectory:
  • leaf node, file or empty file
  • Q: how to count the number of files or directory?

basic class:

• file
• directory
• fileSystem