来自具有 counter++ 变量的方法的 ArrayList

Question

我需要调用方法student，创建一个学生ID，该学生ID从1开始并随着每个新学生的增加而增加，然后将该新学生添加到ArrayList。但是，我的列表只获取最后一次调用的 ID 号并将其提供给列表的所有成员。如果我输入 GPA 3.4 的“James”和 GPA 2.9 的“Jack”，它会返回两个学生的相同学生 ID 为 2。我需要帮助才能让 James 的 ID 为 1，Jack 的 ID 为 2，等等。第一个块来自我的main 方法，最后的第二个块来自类本身。

ArrayList list1 = new ArrayList();
int option = -1;
String name;
double gpa;
Scanner studentInput = new Scanner(System.in);
Scanner gpaInput = new Scanner(System.in);
Scanner optionInput = new Scanner(System.in);
while (option != 0) {
    System.out.println("Please choose an option:");
    System.out.println("0: quit");
    System.out.println("1: Add a student to your list");
    System.out.println("2: Display your student list");
    option = optionInput.nextInt();
    switch (option) {
    case 0:
        System.out.println("Have a good Day!");
        break;
    case 1:
        System.out.println("Please enter the students name.");
        name = studentInput.next();
        System.out.println("Please enter the students GPA.");
        gpa = gpaInput.nextDouble();
        Student studentA = new Student(name, gpa);
        list1.add(studentA);
        break;

    case 2:
        System.out.println("Here is your list so far.");
        for (int i = 0; i < list1.size(); i++) {
            System.out.println(list1.get(i));
        }
    }

}

public class Student implements Comparable {
    private static int studentID = 0;
    private String name;
    private double gpa;

    public Student( String name, double gpa) {
        studentID++;
        this.name = name;
        this.gpa = gpa;
    }

    public int getStudentID() {
        return studentID;
    }

    public void setStudentID(int studentID) {
        this.studentID = studentID;
    }

    public String getName() {
        return name;
    }

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

    public double getGpa() {
        return gpa;
    }

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

Answer 1

类中的studentID 字段在Student 的所有实例之间共享，因此如果其值发生变化，getStudentID 将为所有实例返回新值。要解决此问题，请为学生 ID 添加另一个非静态字段，然后将静态字段的值存储到您刚刚在构造函数中添加的字段中：

public class Student implements Comparable {
    private static int globalStudentID;
    private int studentID;
    private String name;
    private double gpa;

    public Student( String name, double gpa) {
        globalStudentID++;
        this.studentID = globalStudentID;
        this.name = name;
        this.gpa = gpa;
    }

    public int getStudentID() {
        return studentID;
    }

    public void setStudentID(int studentID) {
        this.studentID = studentID;
    }

    // ...
}