Question

我正在尝试为类HthsStudent创建一个构造函数，它从类Student继承变量和状态。（学生从类Person继承变量和状态。）

问题是，java不喜欢我尝试这样做的方式，并且一直告诉我，我正在做的事情是错的，尽管这正是我在课堂上做的那样。它告诉我有一个“无效的方法声明，需要返回类型”错误，但我没有找到解决方法。

我做错了什么，我该如何解决？

谢谢！

/**
 * Write a description of class Persn here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Person
{
String firstName;
String lastName;

public Person (String firstName, String lastName)
{
    this.firstName = firstName;
    this.lastName = lastName;
}

public String toString ()
{
   return lastName + ", " + firstName;
}
}





/**
 * Write a description of class Student here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Student extends Person
{
int gradeLevel;
private static int studentId = 0;

public Student (String firstName, String lastName, int gradeLevel)
{
    super(firstName, lastName);
    this.gradeLevel = gradeLevel;

    if (gradeLevel > 5 || gradeLevel < 0)
    {
        gradeLevel = 0;
    }

    studentId = studentId + 1;
}

public int getLevel()
{
    return gradeLevel;
}

public String toString ()
{
    return lastName + ", " + firstName + "\nGrade Level: " + gradeLevel + "\nID #: " + studentId;
}
}




/**
 * Write a description of class HTHSStudent here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class HTHSStudent extends Student
{
double gpa;

public HthsStudent (String firstName, String lastName, int gradeLevel, double gpa)
{
    super(firstName, LastName, gradeLevel);
    this.gpa = gpa;

    if (gpa > 5.0 || gpa < 1.0)
    {
        gpa = 0.0;
    }


}

public String toString()
{
    return lastName + ", " + firstName + "\nGrade Level: " + gradeLevel + "\nID #: " + studentId + "\nGPA: " + gpa;
}
}

Answer 1

您没有正确地使用最后一堂课。你有：

class HTHSStudent extends Student
{
double gpa;

public HthsStudent (String firstName, String lastName, int gradeLevel, double gpa)

应该是

class HTHSStudent extends Student
{
double gpa;

public HTHSStudent (String firstName, String lastName, int gradeLevel, double gpa)

甚至更好：

class HthsStudent extends Student  {
    private double gpa;

    public HthsStudent (String firstName, String lastName, int gradeLevel, double gpa)

请注意，对于Java标识符，大写很重要

同样如我的评论中所述，您还有另一个不相关的问题，即您的studentId字段绝对应该不是静态的。此字段对于每个 Student对象必须是唯一的，如果您将其设置为静态，它将成为该类的属性，因此对所有学生都是相同的。如果您将其设置为静态以修复编译器错误，那么您修复了错误的错误。正确的解决方法是不要尝试以静态方式引用它，不在课堂上。

父子类的问题

1 个答案: