Module compilation problem

**Application Name:**OpenMRS Version Number: 1.9.3

I am new to openMRs. I have created the first module and edited the codes as per http://en.flossmanuals.net/openmrs-developers-guide/hello-world-module/. All the classes and interfaces/cases(upper/lower) are similar to the details in this link. However, during compilation, these types are displayed; eventhough, there are no logical errors. [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3. 1:compile (default-compile) on project department-api: Compilation failure: Comp ilation failure: [ERROR] /E:/mrsBackup/newModules/department/api/src/main/java/org/openmrs/module /department/api/impl/DepartmentServiceImpl.java:[48,16] cannot find symbol [ERROR] symbol: class List [ERROR] location: class org.openmrs.module.department.api.impl.DepartmentService Impl [ERROR] /E:/mrsBackup/newModules/department/api/src/main/java/org/openmrs/module /department/api/impl/DepartmentServiceImpl.java:[48,21] cannot find symbol [ERROR] symbol: class Department [ERROR] location: class org.openmrs.module.department.api.impl.DepartmentService

How can I overcome this error? Please help