If you are working with a Maven project you have to understand the fact that directory layout is bit different. In this the package name must be src/main/java.
For this update your source folder by right click on project root folder -> properties -> java build path -> source tab. Here remove all other source folders as they might have been added in wrong manner. Now, select project /src/main/java as the source folder. Add and apply the changes. Now refresh your workspace using F5.
This should fix the issue of not recognizing a main type.