How to implement a composite pattern in Java?

I want to implement a composite pattern in Java in order to map a software development organization. So, let's assume there are multiple project managers and multiple developers. Each developer is assigned to exactly one project manager and each developer is able to code in various programming languages. The project managers lead the developers and know exactly their workload.

I am not a hundred percent sure about this design pattern, but I think that it is the perfect use case for this scenario, isn't it?

The result should be as follows:

I want to query the project manager to check the workload of all developers which are able to code in a specific programming language, e.g. Java.

Here is what I have so far:

Employee.java:

public class Employee {

    private String name = null;

    public Employee() {
        name = "Noob";
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

ProgrammingLanguages.java:

public enum ProgrammingLanguages {
    JAVA,
    JAVASCRIPT,
    C,
    PHP,
    SWIFT,
    PYTHON
}

ProjectManager.java:

import java.util.ArrayList; import java.util.List;

public class ProjectManager extends Employee {

private List<Employee> employeeList = null;

public ProjectManager() {
    employeeList = new ArrayList<Employee>();
}

public List<Employee> getEmployees() {
    return employeeList;
}

public void setEmployees(List<Employee> employees) {
    employeeList = employees;
}

public int getTotalWorkload() {
    int workload = 0;
    for (Employee employee : employeeList) {
        workload += employee.getWorkload(); // Error! Cannot resolve method 'getWorkload()'
    }
    return workload;
}

}

Developer:

import java.util.ArrayList; import java.util.List;

public class Developer extends Employee {

private List<ProgrammingLanguages> languagesList = null;

private int workload = 0;

public Developer() {
    languagesList = new ArrayList<ProgrammingLanguages>();
}

public void setLanguagesList(List<ProgrammingLanguages> languagesList) {
    this.languagesList = languagesList;
}

public void addProgrammingLanguage(ProgrammingLanguages language) {
    languagesList.add(language);
}

public List<ProgrammingLanguages> getLanguagesList() {
    return languagesList;
}

public void setWorkload(int workload) {
    this.workload = workload;
}

public int getWorkload() {
    return workload;
}

}

Unfortunately, I get a compiler error in my ProjectManager class, any idea why?

Thanks in advance.