Java-Combat-imported Java projects cannot run the Main method class

The Java project downloaded on the Web, after the import project through the IDE (Eclipse or STS), found that the imported project had only the SRC directory, no JRE System Library, package. Open the class with the main method, right-click the run as, and do not see the Java application. When running with Run as-> Aspectj/java application, an error occurs:

Pop-up error window information:
Editor does not contain a main type

Solving method
The imported project, not a Java project, is not running because it lacks a running environment. Right-click the project-> Properties-> project Facets-> Revert Check java and click OK.
Then again right click on the main method class, run as, you can see the Java application, this can be running.