Enhance class & function documentation in LFUcache.java

[Hardvan]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.56%. Comparing base (842ff52) to head (2fe9cee).
Report is 23 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5583      +/-   ##
============================================
+ Coverage     52.31%   54.56%   +2.24%     
- Complexity     3259     3413     +154     
============================================
  Files           526      535       +9     
  Lines         15205    15383     +178     
  Branches       2892     2935      +43     
============================================
+ Hits           7954     8393     +439     
+ Misses         6924     6637     -287     
- Partials        327      353      +26     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.