StringJoiner cannot be resolved to a type

The error message "StringJoiner cannot be resolved to a type" typically occurs when the Java compiler cannot find the class or interface named "StringJoiner" in the current scope.

To resolve this issue, make sure you have imported the correct class at the top of your Java file:

import java.util.StringJoiner;

If you have already imported the class and are still facing the issue, ensure that you have the correct version of Java that supports StringJoiner. StringJoiner was introduced in Java 8, so if you are using an older version, you may need to upgrade your Java version.

If you are using an IDE, try cleaning and rebuilding your project to refresh the dependencies and resolve any compilation errors.

If none of the above solutions work, please provide more context or code snippets so that I can assist you further.