I just saw a piece of code that had some classes with only one method. I picked an examples:

public class TempDirCleanupProcess {
  public void cleanup(final File directory) {} 

Then, later on in the code the method was called the following way:

new TempDirCleanupProcess().cleanup(tempDir);

Now I am wondering if this is a bad practice because I have seen such "behavior" only with static methods before. Any oppinions on that?

  • With non static methods, every call your TempDirCleanupProcess is constructed anew. If it happens often or it takes much resources you should consider injecting a cleanup service. Static methods are class methods, so they do not have this problem – Mr. Wrong Apr 17 at 10:51
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    The difference is that static methods cannot be overridden, whereas non-static methods can. – MC Emperor Apr 17 at 10:53
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    @MCEmperor but if you're writing new TempDirCleanupProcess(), you're getting that exact class' methods, not an override. – Andy Turner Apr 17 at 10:54
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    One may say it's too broad, or not clear enough, but it's definitely not opinion-based. I am voting to reopen it. – Andrew Tobilko Apr 17 at 11:30

Sure, it could be refactored into a class with a static method. It would obviate the need for creating an instance every time one needs to call the method. In this particular case with no additional context given, a static method would be a nicer solution.

However, don't forget a class can hold a state and a single method may change that state and return a reference to the current object.

public class Builder {
  // state

  public Builder buildPart(T part) { 
      // update the state
      return this;


It would resemble a variation of the builder pattern and make sense.

return new Builder();
return new Builder().buildPart(partA);
return new Builder().buildPart(partA).buildPart(partB);

I can also think of an extremely poor design where this would be leaked out from cleanup, so a reference to that new TempDirCleanupProcess() wouldn't be lost after the line is executed.


It looks like a standard static method, but we don't see all the details

So maybe when you are creating the object you are also creating instance members that are used in the method cleanup and you must create the object in order to make them available


Another approach would be to have a Directory class like such

Directory temp = new Directory('path/to/file');

This also allows you to inherit the Directory class in some other class that requires all of these utility functions.

That being said, a utility function in a class like yours should be static.

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    It must not be static because it would introduce hard & hidden coupling and will make testing a nightmare. – Svetlin Zarev Apr 17 at 11:05
  • @SvetlinZarev you could use PowerMockito.mockStatic. – DodgyCodeException Apr 17 at 11:15
  • Of course you can, but if you have to cheat, then your design is shit. – Svetlin Zarev Apr 17 at 11:27
  • @SvetlinZarev Are you saying the method itself would be a testing nightmare or that using the method in other code would be a testing nightmare? If the former, it shouldn't be any harder to test than testing an instance method—assuming the method is effectively self-contained. If the latter, you could always abstract the call to the method, allowing you to mock it at the call site (though this may not be acceptable/desirable). – Slaw Apr 17 at 11:27
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    I'm saying that using static methods is bad practice. The simplest real world case is introducing a hidden dependency to System.getProperty or the like - imagine a test that depends on system properties and it fails because some other test had set some property. you could always abstract the call to the method -> Of course you can abstract it using an interface, but then it's not a static method anymore, is it ? Then you have a polymorphic call, not a call to static method. You have a dependency to an abstraction, not a concrete class. – Svetlin Zarev Apr 17 at 11:31

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