How to solve when the startup class cannot be found when implementing an idea into a project?

To resolve the issue of not finding the startup class, you can try the following steps:

1. Confirm whether the entry class of the project exists: Check the project’s source code to see if there is a class annotated with @SpringBootApplication or @EnableAutoConfiguration, which are typically used to identify the entry class of the project.
2. Check the dependencies of the project to ensure they are correct. Look in the pom.xml file for Maven projects or build.gradle file for Gradle projects to verify that the proper dependencies have been included. Pay special attention to see if Spring Boot Starter dependencies, such as spring-boot-starter-web for developing web applications, have been added.
3. Check the directory structure of the project: make sure that the source code of the project is organized according to the standard Maven or Gradle project structure. Typically, the main class should be located in the appropriate package under the src/main/java directory.
4. Clean and rebuild the project: If the above steps do not solve the problem, you can try deleting the target or build directory of the project and rebuild the entire project.
5. Check IDE configuration: If you are running the project in a specific Integrated Development Environment (IDE), make sure to check the IDE configuration to ensure that the correct entry class for the project is specified.
6. Check the startup configuration of the project: Some projects may have customized startup configuration files (such as application.properties or application.yml), in which it may be necessary to explicitly specify the path of the startup class.

If the above steps do not resolve the issue, you can try asking in developer communities or forums for more specific assistance.