toString() 只打印默认值

Question

我正在尝试使用 toString() 方法来打印一些私有字段。但是，每当我尝试将适当类的对象发送到打印方法时，它只会打印出每个字段的默认值，无论我将它们更改为什么。任何帮助将不胜感激:) 这是带有 toString() 方法的类（它还覆盖了另一个类，它是 getter 的来源）。对不起，我编辑这篇文章的速度很慢。不熟悉这里的文本编辑器。

人物类

public class Person
{
// Declare all the fields as strings
private String firstName = "", lastName = "", address = "", zipcode = "",
        phone = "";  // There are accessors and mutators for these as well
public String toString()
{
        String str = "First name: " + firstName + "...Last name: " + lastName + 
                "... Street address: " + address + "... Zipcode: " + zipcode + 
                "... Phone number: " + phone;

    return str;
}

学生班

  public class Student extends Person
  {
    // declare fields that are not in Person
    private String major = "";
    private double gpa;

        // Declare accessor and mutator methods for the fields
        public String getMajor()
        {
            return major;
        }

    public void setMajor(String major)
    {
        this.major = major;
    }

    public double getGpa()
    {
        return gpa;
    }

    public void setGpa(double gpa)
    {
        this.gpa = gpa;
    }


    // Create a toString method that overrides the one in Person
    public String toString()
    {
        String str = "First name: " + getFirstName() + "...Last name: " + 
                getLastName() + "... Street address: " + getAddress() + 
                "... Zipcode: " + getZipcode() + "... Phone number: " +
                getPhone() + "... Grade point average: " + getGpa() +
                "...Major: " + getMajor();

        return str;
    }
}

这是整个主课......其中很多都是乏味的代码，因为它是家庭作业，但主要思想是： “编写一个名为 CollegeList 的应用程序，声明一个包含 4 个“常规”CollegeEmployees、3 个教员和 7 个学生的数组。提示用户指定将输入哪种类型的人员数据（'C'、'F' 或 'S' )，或允许用户退出 ('Q')。当用户选择继续（即不退出）时，接受适当类型人员的数据输入。如果用户尝试输入数据超过 4 名大学员工、3 名教职员工或 7 名学生显示错误消息。当用户退出时，在屏幕上显示一个报告，在适当的标题“学院员工”、“教师”或“学生”下列出每组人员。如果用户在会话期间没有为一种或多种类型的人输入数据，请在适当的标题下显示适当的消息。

主类

import java.util.Scanner;  // Needed for Scanner class

public class CollegeList
{

/**
 * @param args the command line arguments
 */
public static void main(String[] args)
{
    // Declare the arrays of people
    Person[] people = new Person[14];

    // These three arrays are being made to print out the types of people
    // at the end neatly
    Faculty[] fArray = new Faculty[4];
    Student[] sArray = new Student[7];
    CollegeEmployee[] cArray = new CollegeEmployee[3];

    // Prompt for users input
    System.out.print("Please choose the type of person you are entering " +
            "data for.\nFor a student enter \"S\"; for a faculty member " +
            "enter \"F\"; for a college employee enter \"C\"; and to quit " 
            + "enter \"Q\": ");

    Scanner keyboard = new Scanner(System.in);
    String type = keyboard.next();  // the type of person
    System.out.println();

    // initialize counts of persons so that user does not enter more
    int facultyCount = 0;
    int studentCount = 0;
    int employeeCount = 0;

    // initialize index of the array to 0
    int index = 0;

    // continue until the user enters Q or until one of the types of people
    // overflows or until all 14 elements are taken up
    while (!type.equals("Q") && (facultyCount <= 3) && (studentCount <= 7)
            && (employeeCount <= 4) && (index < 14))
    {
        if(type.equals("S") && !type.equals("Q")) // Enter info for student
        {
            // Give the indexes the adresses
            people[index] = new Student();
            sArray[studentCount] = new Student();

            // Set the info
            personInfo(people[index]);
            studentInfo((Student)people[index]);
            System.out.println("\n");

            // Increment the counts
            studentCount++;
            index++;
        }

        else if(type.equals("C") && !type.equals("Q")) // Enter info for
        {                                              // college employee
            // Give the indexes the adresses
            people[index] = new CollegeEmployee();
            cArray[employeeCount] = new CollegeEmployee();

            // Set the info
            personInfo(people[index]);
            employeeInfo((CollegeEmployee)people[index]);
            System.out.println("\n");

            // Increment the counts
            employeeCount++;
            index++;
        }

        else if(type.equals("F") && !type.equals("Q")) // enter info for faculty
        {
            // Give the indexes the adresses
            people[index] = new Faculty();
            fArray[facultyCount] = new Faculty();

            // Set the info
            personInfo(people[index]);
            employeeInfo((CollegeEmployee)people[index]);
            facultyInfo((Faculty)people[index]);
            System.out.println("\n");

            // increment the counts
            facultyCount++;
            index++;
        }

        System.out.print("Please enter the next person type (S, C, F, " +
                "or Q): ");
        type = keyboard.next();
    }

    // Displays error message then closes program if there was overflow
    if ((facultyCount > 3) || (studentCount > 7) || (employeeCount > 4))
    {
        System.out.println("Too much data for one type of  person. Goodbye.");
        System.exit(0);
    }


    // Print the data for all of the college employees
    System.out.println("\n\n");
    System.out.println("THE COLLEGE EMPLOYEES");
    for (int i = 0; i < employeeCount; i++)
    {
        System.out.println(cArray[i]);
        System.out.println("\n");
    }
    // Determines if not all of the personS type was filled
    if (employeeCount != 4)
    {
        System.out.println("There are " + (4 - employeeCount) + " employees"
                + " who are not recorded.");
    }



    // Print the data for all of the faculty
    System.out.println("\n\n");
    System.out.println("THE FACULTY");
    for (int i = 0; i < facultyCount; i++)
    {
        System.out.println(fArray[i]);
        System.out.println("\n");
    }
    // Determines if not all of the person type was filled
    if (facultyCount != 3)
    {
        System.out.println("There are " + (3 - facultyCount) + " faculty "
                + "members who are not recorded.");
    }



    // Print the data for all of the students
    System.out.println("\n\n");
    System.out.println("THE STUDENTS");
    for (int i = 0; i < studentCount; i++)
    {
        System.out.println(sArray[i]);
        System.out.println("\n");
    }
    // Determines if not all of the person type was filled
    if (studentCount != 7)
    {
        System.out.println("There are " + (7 - studentCount) + " students "
                + "who are not recorded.");
    }
}

// prompts the user for data input that is universal to all the people
public static void personInfo(Person p)
{
    Scanner keyboard = new Scanner(System.in);

    System.out.print("First name: ");
    String fName = keyboard.nextLine();
    System.out.println();

    System.out.print("Last name: ");
    String lName = keyboard.nextLine();
    System.out.println();

    System.out.print("Street address: ");
    String address = keyboard.nextLine();
    System.out.println();

    System.out.print("Zipcode: ");
    String zipcode = keyboard.nextLine();
    System.out.println();

    System.out.print("Phone number: ");
    String phone = keyboard.nextLine();
    System.out.println();

    // Sets the data accordingly
    p.setFirstName(fName);
    p.setLastName(lName);
    p.setAddress(address);
    p.setZipcode(zipcode);
    p.setPhone(phone);
}

// Sets the data for student fields
public static void studentInfo(Student s)
{
    Scanner keyboard = new Scanner(System.in);

    System.out.print("Grade point average: ");
    double gpa = keyboard.nextDouble();
    System.out.println();

    System.out.print("Major: ");
    String major = keyboard.next();
    System.out.println();

    // Set the data accordingly
    s.setGpa(gpa);
    s.setMajor(major);
}

// Sets the data for Faculty fields
public static void facultyInfo(Faculty f)
{
    Scanner keyboard = new Scanner(System.in);

    System.out.println("Is the faculty tenured (\"yes\" or \"no)\"?");
    String tenured = keyboard.next();

    // set the data accordingly
    switch (tenured)
    {
        case "yes" :
            f.setTenured(true);
            break;
        case "no" :
            f.setTenured(false);
            break;
    }
}

// Sets the info for CollegeEmployee fields
public static void employeeInfo(CollegeEmployee c)
{
    Scanner keyboard = new Scanner(System.in);

    System.out.print("Social security number: ");
    String socialSecurity = keyboard.next();
    System.out.println();

    System.out.print("Salary: ");
    String salary = keyboard.next();
    System.out.println();

    System.out.print("Department name: ");
    String department = keyboard.next();
    System.out.println();

    // Set the data accordingly
    c.setSocialSecurity(socialSecurity);
    c.setSalary(salary);
    c.setDepartment(department);
}

}

Answer 1

您正在为每个条目创建两个 Student() 实例。您只更新了 people 数组中的那个，而不是 student 数组。

   people[index] = new Student();
   sArray[studentCount] = new Student();

假设您确实想将学生存储在两个数组中，请将其更改为：

Student student = new Student();
people[index] = student;
sArray[studentCount] = student;

Answer 2

由于我没有你的 Person 类实现，我只是忽略了 Person 类。这是我的代码：

public class Student
{
    // declare fields that are not in Person
    private String major = "";
    private double gpa;

    // Declare accessor and mutator methods for the fields
    public String getMajor()
    {
        return major;
    }

    public void setMajor(String major)
    {
        this.major = major;
    }

    public double getGpa()
    {
        return gpa;
    }

    public void setGpa(double gpa)
    {
        this.gpa = gpa;
    }


    // Create a toString method that overrides the one in Person
    public String toString()
    {
        String str = "Grade point average: " + getGpa() +
                "...Major: " + getMajor();

        return str;
    }
    public static void main(String [] args)
    {
        Student s = new Student();
        s.setGpa(8.88);
        s.setMajor("CS");
        System.out.println(s);
    }
}

这是输出：

平均绩点：8.88...专业：CS

可能你在打印之前没有设置对象的字段。

Answer 3

您可以添加一个包含所有字段的构造函数

public class Person {

    private String firstName = "";
    private String lastName = "";
    private String address = "";
    private String zipcode = "";
    private String phone = "";

    public Person(String firstName,
                  String lastName,
                  String address,
                  String zipcode,
                  String phone) {

        this. firstName = firstName;
        this.lastName = lastName;
        this.address = address;
        this.zipcose = zipcode;
        this.phone = phone;

    }
}

main

public static void main(String[] args){
    Person person = new Person(
           "John", "Smith", "444 Some Lame St", "90210", "510-555-5555");

    System.out.println(person);
}

Answer 4

我认为您不应该在 Student 中调用 Person 的 getter 来执行 toString，而应该执行以下操作：

return super.toString() + "... Grade Point Average: " + this.gpa + 等Student 不必知道Person 想要显示为字符串的信息。它应该只返回 Person 想要显示的任何内容以及 Student 想要显示的任何内容。

话虽如此，我同意其他答案，即您实际上并未在Student 中设置任何内容。能否请您发布您的主要方法？

编辑：现在您已经发布了您的主要方法，我可以看到您的问题。您插入到people 数组中的Person 与您插入到c/s/fArray 中的对象不同。因此，当您打印 c/s/fArray 时，您实际上是在打印未初始化的对象。如果您想保留对象的副本，您应该执行以下操作：

people[index] = new Faculty();
fArray[facultyCount] = people[index];

那么people[index] 和fArray[facultyCount] 都是一样的。

同样，您不应该使用静态方法来初始化对象，而应该在这些对象的构造函数中这样做。