Extension incorrectly runs cached `.class` file from another class of same name with no `package`

[aatle]

Bug report

Suppose there is a file structure:

folder1/
    Main.java
folder2/
    Main.java

// folder1/Main.java
public class Main {
    public static void main(String[] args) {
        System.out.println("Main 1");
    }
}

// folder2/Main.java
public class Main {
    public static void main(String[] args) {
        System.out.println("Main 2");
    }
}

No package statements; the projects are not connected at all.

When folder1/Main.java is run first, it gives the correct output Main 1.
But if folder2/Main.java is then run, it gives the wrong output of Main 1 instead of Main 2; the first built file is run instead.
folder1/Main.java 'shadows' folder2/Main.java, since the class name is the same and there are no package statements.
Another file structure that causes this is ./Main.java, ./folder/Main.java

This bug is inconvenient when multiple different, unrelated Java projects are in the same workspace.

[github-actions]

Hi @aatle, I'm an AI Support assistant here to help with your issue. While the team reviews your request, I wanted to provide some possible tips and documentation that might help you in the meantime.

Workarounds and Suggestions

• Declare an explicit package in each directory to avoid name collisions, e.g.

  // folder1/Main.java
  package folder1;
  public class Main { … }
  
  // folder2/Main.java
  package folder2;
  public class Main { … }

  (see Unable to determine the scope of the class redhat-developer/vscode-java#541 (comment))

• Open each project in its own VS Code workspace, or whitelist only one source folder at a time via java.project.sourcePaths in your settings. This prevents the language server from loading both folders simultaneously.

• Run the Java: Clean the Java Language Server Workspace command (F1) after switching between directories to flush cached .class files.

Tracking

This behavior is a known issue in the VS Code Java extension where classes with identical names in different folders share a cache. It is being tracked here:

• Run/debug multiple single file programs with the same name redhat-developer/vscode-java#1645

No fix is available yet to automatically isolate runs of same-named single-file programs.

The team will respond to your issue shortly. I hope these suggestions are helpful in the meantime. If this comment helped you, please give it a 👍. If the suggestion was not helpful or incorrect, please give it a 👎. Your feedback helps us improve!