在seeStaff方法中，您正在创建HospitalStaff的一个新示例，该示例在创建时没有staff成员。因此，当您在该空示例中迭代staff成员列表时，不会得到输出。您在main()中创建了HospitalStaff的另一个示例，但不对该示例执行任何操作。
解决这个问题的一种方法是先创建HospitalStaff示例，然后在创建Hospital示例时，将HospitalStaff示例传递给Hospital的构造函数，以便将其存储在示例中，然后showStaff方法可以打印HospitalStaff示例中的值，如下所示：

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

public class Test {

    public static void main(String[] args) {

        // Create an object containing the hospital's staff
        HospitalStaff hs = new HospitalStaff();
        hs.addHospitalStaff("A103", "Name1", "Lastname1", "Surgery", "Doctor");
        hs.addHospitalStaff("A124", "Name2", "Lastname2", "Surgery", "Doctor");

        // Create a Hospital object, passing it the `HospitalStaff` instance containing the hospital's staff.
        Hospital h = new Hospital(hs);
        h.Hospitalinformation();

        h.seeStaff();  // <- Print a list of hospital staff members
    }

}
/* This is the Hospital class. It has 3 methods. The HospitalInformation method prints the name and the address, name, email address and phone number of the hospital.
 * It declares and array list by the name of listofStaff of the type HospitalStaff.
 * It consists of a seeStaff method which is supposed to show all staff working at the hospital.
 */

class Hospital{
    public String name = "Red Cross";
    public String Address = "whatever";
    public String phonenum = "whatever2";
    private String email = "whatever@gmail.com";

    private HospitalStaff hs;

    public Hospital(HospitalStaff hs) {
        this.hs = hs;  // <- Associate the passed in HospitalStaff instance with this `Hospital` instance.
    }

    public void Hospitalinformation() {
        System.out.println("The name of the hospital is: " +name + " \nThe name of the Address: " + Address + "\nPhone number: "+phonenum + " \nEmail Address: " + email);
    }

    // Print the members of the hospital's staff
    public void seeStaff() {
        
        for(String stafflist: hs.listofStaff) {
            System.out.println(stafflist);
        }
    }

}

/*The Hospital Staff method consists of toString method as well as a addHospitalStaff method.
 * The seeStaff method is added for debugging purposes, it is however, supposed to exist in the Hospital method.
 */
class HospitalStaff {

    private String StaffId;
    public String firstname;
    public String lastname;
    public String department;
    public String stafftype;
    List<String>listofStaff =  new ArrayList<String>();

    public void addHospitalStaff(String StaffId, String firstname, String lastname, String department, String stafftype) {
        String here = StafftoString(StaffId, firstname, lastname, department, stafftype);
        listofStaff.add(here);
    }
    public String StafftoString(String StaffId, String firstname, String lastname, String department, String stafftype) {
        return String.valueOf(firstname) + " " + String.valueOf(lastname) +" " + String.valueOf(StaffId) +" " + String.valueOf(department) +" " + String.valueOf(stafftype);
    }
    public void seeStaff() {
        for(String stafflist: listofStaff) {
            System.out.println(stafflist);
        }
    }

}

结果：

The name of the hospital is: Red Cross 
The name of the Address: whatever
Phone number: whatever2 
Email Address: whatever@gmail.com
Name1 Lastname1 A103 Surgery Doctor
Name2 Lastname2 A124 Surgery Doctor