打印數組列表中的對象

Question

我正在 Java 做一個醫院管理系統項目。我有 3 個班級。 一個 class 有主要方法，另一個 class 是醫院 class，它有方法打印出醫院的詳細信息，另一個方法打印出醫院的工作人員。 第三個 class 是 HospitalStaff class，它有一個用於員工所有詳細信息的 toString 方法和一個 addStaff 方法。 員工被添加到 arraylist 中。我想要打印所有員工的方法存在於醫院 class 中，我該怎么做？

這是我的代碼：

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

public class HospitalProject {

    public static void main(String[] args) {
        Hospital h = new Hospital();
        h.Hospitalinformation();
        HospitalStaff hs = new HospitalStaff();
        hs.addHospitalStaff("A103", "Name1", "Lastname1", "Surgery", "Doctor");
        hs.addHospitalStaff("A124", "Name2", "Lastname2", "Surgery", "Doctor");
        
        
    }

}
/* 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";
    
    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);
    }
    public void seeStaff() {
        HospitalStaff hs1 = new HospitalStaff();
        for(String stafflist: hs1.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);
        }
    }

}

我嘗試在 Hospital class 中創建一個名為 seeStaff() 的方法，並在該方法中創建了一個名為“hs1”的 HospitalStaff object。 然后，我使用 HospitalStaff object 調用在 HospitalStaff class 中創建的 arraylist（稱為 listofStaff）。我在 for each 循環中將其用作（String stafflist：hs1.listofStaff）。 但是，當我在 main 中創建 Hospital class object 並調用 seeStaff() 方法時，它不會打印任何內容。 我不確定為什么會這樣。

Answer 1

在您的seeStaff方法中，您正在創建HospitalStaff的新實例，創建時其中沒有任何工作人員。 因此，當您遍歷該空實例中的工作人員列表時，您不會得到 output。您在main()中創建了另一個HospitalStaff實例，但您不對該實例執行任何操作。

解決此問題的一種方法是首先創建您的HospitalStaff實例。 然后，當您創建Hospital實例時，將HospitalStaff實例傳遞到Hospital的構造函數中，以便它可以存儲在實例中。 然后您的showStaff方法可以打印HospitalStaff實例中的值。 這是它的樣子：

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);
        }
    }

}

結果：

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