I am using Spotbugs plugin within Eclipse IDE. I can run the Spotbugs over a whole project, which gives me the impression that the tool needs to build the project to present its analysis report.
But the documentation says that it's a static analysis tool.
So, I was curious if it requires to build the project, then can we call it a Static Analysis Tool? And if it doesn't require to build the project, can we run Spotbugs on single .java files?
The meaning of static analysis is that it analyses your project files "at rest", as opposed to monitoring a running application. https://en.wikipedia.org/wiki/Static_program_analysis
Analyzing bytecode has both strengths and weaknesses compared to analysing source code. It's faster, and better suited to deep analysis of program flow, but won't pick up mistakes that get compiled away, like unnecessary imports and inconsistent-but-legal whitespace.
You can't properly run it on a single file, even if you compiled that file, because there are detectors that take multiple files into consideration, eg detecting when you try to pass null to a method whose parameters are annotated as non-null, or when you've defined a method as public and then never called it from outside the class.