對另一個類中的非靜態方法進行靜態引用

Question

我正在 Java 課程中學習面向對象編程，我正在做一個項目，其中程序創建三種類型的對象：地址、日期和員工。 該程序存儲多個員工的數據，然后將數據顯示在 Employee 類型的數組中。

我使用了四個不同的類： Address類、 Date類和Employee類，以及創建數組的EmployeeTest類。

這是地址類：

public class Address {

    private String Street;
    private String City;
    private String State;
    private int ZipCode;

    public Address(String St, String Ci, String Sta, int Zip){
        Street = St;
        City = Ci;
        State = Sta;
        ZipCode = Zip;
    }

    public String getEmployeeAddress(){
        return (Street + ", " + City + ", " + State + " " + ZipCode);
    }
}

日期類：

public class Date {

    private int Month;
    private int Day;
    private int Year;

    public Date(int M, int D, int Y){
        Month = M;
        Day = D;
        Year = Y;
    }

    public String getDateString(){
        return (Month + "/" + Day + "/" + Year);
    }
}

而且，員工類：

public class Employee {
    private int EmployeeNum;

    public void setEmployeeNum(int ENum){
        EmployeeNum = ENum;
    }

    public int getNum(){
        return EmployeeNum;
    }

    public String getDate(){
        return Date.getDateString();
    }

    public String getName(){
        return Name.getEmployeeName();
    }
    public String getAddress(){
        return Address.getEmployeeAddress();
    }

}

所有這些類都在同一個包中（我使用的是 Eclipse）。 Employee 類的重點是創建一個 Employee 類型的對象，並能夠使用 Address、Name 和 Date 類獲取它的 Address、Name 和 HireDate。

數組發揮作用的地方在這里：

import java.util.Scanner;
import java.lang.*;

public class EmployeeTest {

    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        System.out.print("How many employees will have their data stored today?");
        int EmployeeAmount = Integer.parseInt(input.nextLine());

        Employee [] EmployeeArray = new Employee[EmployeeAmount];

        for (int i = 0; i < EmployeeArray.length; i ++){
            System.out.print("What is employee " + (i+1) + "'s employee number?");
            int EmployeeNumber = Integer.parseInt(input.nextLine());
            EmployeeArray[i] =  new Employee();
            EmployeeArray[i].setEmployeeNum(EmployeeNumber);

            System.out.println("What is the first name of employee " + EmployeeNumber + "?");
            String EmployeeFirstName = input.nextLine();

            System.out.println("What is the last name of employee " + EmployeeNumber + "?");
            String EmployeeLastName = input.nextLine();

            Name EmployeeName = new Name(EmployeeFirstName, EmployeeLastName);

            System.out.println("Please enter the street address: ");
            String StreetAddress = input.nextLine();
            System.out.println("Please enter the name of the city: ");
            String CityName = input.nextLine();
            System.out.println("Please enter the two character code for the state: ");
            String StateID = input.nextLine();
            System.out.println("Please enter this address's zip code: ");
            int ZipCode = Integer.parseInt(input.nextLine());

            Address EmployeeAddress = new Address(StreetAddress, CityName, StateID, ZipCode);

            System.out.println("Finally, what was the month(#) of the hire date?");
            int Month = Integer.parseInt(input.nextLine());
            System.out.println("What was the day(#)?");
            int Day = Integer.parseInt(input.nextLine());
            System.out.println("What was the year?");
            int Year = Integer.parseInt(input.nextLine());

            Date HireDate = new Date(Month, Day, Year);



        }

        for (int j = 0; j < EmployeeArray.length; j ++){
            System.out.println("Employee number: " + EmployeeArray[j].getNum());
            System.out.println("Employee Name: " + EmployeeArray[j].getName());
            System.out.println("Employee Address: " + EmployeeArray[j].getAddress());
            System.out.println("Employee Hiredate: " + EmployeeArray[j].getDate());
        }


    }

}

該程序提示用戶輸入要存儲在數組中的Employee[] ，然后創建一個大小為EmployeeAmount的Employee[] 。 代碼的思路是，對於Array中的每個Employee，獲取其他類中的所有變量：Employee Number, Employee Name (first and last), Address (Street Address, City, State Code, Zip Code),雇用日期（月、日、年）。 獲得所有這些之后，第二個for循環遍歷每個 Employee 並顯示信息。

我遇到的問題是，在Employee類中，Eclipse 在getDate() 、 getName()和getAddress()方法中給了我一個錯誤。 例如，當我說return Date.getDateString() ，Eclipse 說我不能對非靜態方法進行靜態引用。 解決方案是將getDateString()靜態，我嘗試了此方法，但問題是通過使 Address、Employee 和 Date 類中的所有方法和變量，值被鎖定。 這意味着將為所有員工顯示相同的數據。

這就是我的意思。 如果我將所有方法和變量設為靜態，下面是一個示例輸出。 星號之間的文本是用戶輸入的內容。

How many employees will have their data stored today?**2** What is employee 1's employee number?**1** What is the first name of employee 1? **Bob** What is the last name of employee 1? **Jones** Please enter the street address: **300 1st Avenue** Please enter the name of the city: **New York** Please enter the two character code for the state: **NY** Please enter this address's zip code: **10001** Finally, what was the month(#) of the hire date? **1** What was the day(#)? **1** What was the year? **2001** What is employee 2's employee number?**2** What is the first name of employee 2? **Bobby** What is the last name of employee 2? **Robinson** Please enter the street address: **301 1st Avenue** Please enter the name of the city: **Los Angeles** Please enter the two character code for the state: **CA** Please enter this address's zip code: **90001** Finally, what was the month(#) of the hire date? **1** What was the day(#)? **2** What was the year? **2004** Employee number: 2 Employee Name: Bobby Robinson Employee Address: 301 1st Avenue, Los Angeles, CA 90001 Employee Hiredate: 1/2/2004 Employee number: 2 Employee Name: Bobby Robinson Employee Address: 301 1st Avenue, Los Angeles, CA 90001 Employee Hiredate: 1/2/2004

通過將所有變量和方法設為靜態，值被鎖定，如圖所示，這使得程序無用。 有沒有人有解決這個問題的方法？ 我需要一種方法來顯示每個員工的信息，同時引用其他類中的方法。 現在，通常我只會在一個名為Employee類下創建所有變量和方法，但分配說明指定我需要創建單獨的類。

Answer 1

您正在為 for 循環的每次迭代創建Name 、 Address和Date 。 但是您沒有辦法，也沒有在每個Employee實例上設置它們。

您需要添加方法來設置每個員工的值並存儲信息。 像這樣的東西：

public class Employee {
    private int employeeNum;
    private Name name;
    private Date hireDate;
    private Address address;


    public void setEmployeeNum(int eNum){
        employeeNum = eNum;
    }

    public int getEmployeeNum(){
        return employeeNum;
    }

    public void setHireDate(Date date){
        this.hireDate = date;
    }

    public String getHireDate(){
        return hireDate.getDateString();
    }

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

    public String getName(){
        return name.getEmployeeName();
    }

    public void setAddress(Address addy){
        this.address = addy;
    }

    public String getAddress(){
        return address.getEmployeeAddress();
    }
}

然后在您的 for 循環中，設置值：

  EmployeeArray[i].setName(EmployeeName);
  EmployeeArray[i].setAddress(EmployeeAddress);
  EmployeeArray[i].setHireDate(HireDate);

順便說一句，您不應該將變量大寫，而應該將類大寫。 變量應該是駝峰式的。