How to avoid VS Code warning: “[myfile].java is a non-project file, only syntax errors are reported”

Question

I am running a build task in a java project in Visual Studio Code. The warning in the "PROBLEMS" tab:

[myfile].java is a non-project file, only

Answer 1

Try cleaning the Java language server workspace:

1. CMD+SHIFT+P (CTRL+SHIFT+P ON WINDOWS) to show command palette
2. Choose "Java: Clean the Java language server workspace"
3. Restart and Delete

Just worked for me.