Hello, everyone!

I have a project (related to graph algorithms). It is written by someone else.

The code is horrible:

• public fields, no getters/setters
• huge methods, all public
• some classes have over 20 fields
• some classes have over 5 constructors (which are also huge)
• some of those constructors just left many fields null
  (so I can't make some fields final, because then every second constructor signals errors)
• methods and classes rely on each other in both directions

I have to rewrite this into a clean and understandable API.

Problem is: I myself don't understand anything in this code.

Please give me hints on analyzing and understanding such code.

I was thinking, perhaps, there are tools which perform static code analysis and give me call graphs and things like this.