Most Util classes are bad because:
- They broaden the scope of methods. They make code public that would otherwise be private. If the util method is needed by multiple callers in separate classes and is stable (i.e. doesn't need updating) it's better in my opinion to copy and paste private helper methods into the calling class. Once you expose it as an API, you make it harder to understand what the public entry point to a jar component is (you maintain a tree structured called hierarchy with one parent per method. This is easier to mentally segregate into components which is harder when you have methods called from multiple parent methods).
- They result in dead code. Util methods over time become unused as your app evolves and you end up with unused code polluting your code base. If it had remained private your compiler would tell you the method is unused and you could just remove it (the best code is no code at all). Once you make such a method non private your computer will be powerless to help you remove unused code. It may be called from a different jar file for all the computer knows.
There are some analogies to static vs dynamic libraries.
