Perfect solution to Eclipse project's red exclamation point problem

Reason: the red exclamation point is displayed because the jar package has the wrong path

Solution: right click Build Path - on the project > Configure Build Paht... (or Propertise - > Java Build Path), Libraries in Java Build Path, the package with the Red Cross is the package with the wrong path.

After processing, you can go back to the refresh project. This problem is usually caused by importing someone else's project or some previous JAR package and moving its storage location.

PS: yellow shield exclamation point on the project, indicating that the jar package is referenced, but the jar package is not actually used (it can be understood that the variable is defined, but it has never been used in the future)