對另一個類中的非靜態方法進行靜態引用

Question

我在Java課程中學習面向對象的編程，我正在做一個項目，其中程序創建三種類型的對象：Address，Date和僱員。該程序存儲多個員工的數據，然後將數據顯示在Employee類型的數組中。

我使用四種不同的類：一個Address類，一類Date和Employee類，並且創建該陣列的EmployeeTest類。

下面是Address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); 
    } 
} 

Date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，Employee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(); 
    } 

} 

所有這些類是在同一包（我使用Eclipse）。 Employee類的要點是創建一個Employee類型的對象，並能夠使用Address，Name和Date類獲取它的Address，Name和HireDate。

其中數組發揮作用的地方就在這裏：

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()); 
     } 


    } 

} 

程序提示存儲陣列中的用戶員工的數量，然後創建大小EmployeeAmount的Employee[]。代碼的想法是，對於Array中的每個Employee，都會獲得其他類中的所有變量：Employee Number，Employee Name（first and last），Address（街道地址，城市，州代碼，郵政編碼），聘用日期（月，日，年）。在獲得所有這些信息後，第二個for循環遍歷每個員工並顯示信息。

我遇到的問題是在Employee類中，Eclipse給我提供了getDate(),getName()和getAddress()方法的錯誤。例如，當我說return Date.getDateString()時，Eclipse說我不能對非靜態方法進行靜態引用。它的解決辦法是使getDateString()成爲靜態的，我試過這個，但問題是通過在Address，Employee和Date類中創建所有的方法和變量，這些值被鎖定。這意味着將爲所有員工顯示相同的數據。

這是我的意思。下面是一個示例輸出，如果我使所有的方法和變量都是靜態的。星號之間的文字是用戶輸入的內容。

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

通過使所有的變量和靜態方法的，這些值被鎖定如圖所示，這使得程序無用。有沒有人有解決這個問題？我需要一種方式來顯示每個員工的信息，同時引用其他類中的方法。現在，通常我會在一個名爲Employee的類中創建所有變量和方法，但賦值說明指定我需要創建單個類。

Answer 1

您正在爲for循環的每次迭代創建一個Name,Address和Date。但是你沒有辦法，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。事情是這樣的：

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(); 
    } 
} 

然後在你的for循環中，設置的值：

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

順便說一句，你不應該大寫的變量，只有類。 變量應該是駱駝式的。