对另一个类中的非静态方法进行静态引用

Question

我正在学习 Java 课程中的面向对象编程，并且我正在做一个项目，其中程序创建三种类型的对象：地址、日期和员工。该程序存储了几个员工的数据，然后将数据显示在 Employee 类型的数组中。

我使用了四个不同的类：Address 类、Date 类、Employee 类和创建数组的EmployeeTest 类。

这是地址类：

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);
    }
}

日期类：

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);
    }
}

还有，员工类：

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();
    }

}

所有这些类都在同一个包中（我使用的是 Eclipse）。 Employee 类的重点是创建一个 Employee 类型的对象，并能够使用 Address、Name 和 Date 类获取它的 Address、Name 和 HireDate。

数组发挥作用的地方在这里：

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());
        }


    }

}

程序提示用户输入要存储在数组中的员工人数，然后创建一个大小为EmployeeAmount 的Employee[]。代码的思路是，对于 Array 中的每个 Employee，获取其他类中的所有变量：Employee Number，Employee Name（first and last），Address（街道地址，City，State Code，Zip Code），雇用日期（月、日、年）。获得所有这些后，第二个for 循环遍历每个 Employee 并显示信息。

我遇到的问题是在Employeeclass 中，Eclipse 在getDate()、getName() 和getAddress() 方法中给了我一个错误。例如，当我说return Date.getDateString() 时，Eclipse 说我不能对非静态方法进行静态引用。它的解决方案是使getDateString() 静态，我尝试了这个，但问题是通过使Address、Employee 和Date 类中的所有方法和变量，值被锁定。这意味着将为所有员工显示相同的数据。

这就是我的意思。如果我将所有方法和变量设为静态，下面是一个示例输出。星号之间的文本是用户输入的内容。

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

通过将所有变量和方法设置为静态，如图所示，值被锁定，这使程序无用。有没有人可以解决这个问题？我需要一种方法来显示每个员工的信息，同时引用其他类中的方法。现在，通常我会在一个名为Employee 的类下创建所有变量和方法，但赋值指令指定我需要创建单独的类。

Answer 1

您正在为 for 循环的每次迭代创建 Name、Address 和 Date。但是您没有办法，也没有在每个Employee 实例上设置它们。

您需要添加方法来设置每个员工的值并存储信息。像这样的：

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();
    }
}

然后在你的 for 循环中，设置值：

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

顺便说一句，你不应该大写变量，只有类。 变量应该是驼峰式的。