java - 将学生分配到类(class)中

Question

这个问题已经有答案了:

What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? (25 个回答)

已关闭 4 年前。

线程“main”中出现异常 javalangIndexOutOfBoundsException在此处输入代码类(class)类别

public class Course implements Serializable {
    int id;
    String name;
    Subject subjects;
    Teacher teachers;
    List <User> students;
    List<Student> listOfStudentss = new ArrayList<Student>();
    public int getId() {
        return id;
    }

    public List<Student> getListOfStudentss() {
        return listOfStudentss;
    }

    public void setListOfStudentss(List<Student> listOfStudentss) {
        this.listOfStudentss = listOfStudentss;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public Subject getSubjects() {
        return subjects;
    }

    public void setSubjects(Subject subjects) {
        this.subjects = subjects;
    }

    public Teacher getTeachers() {
        return teachers;
    }

    public void setTeachers(Teacher teachers) {
        this.teachers = teachers;
    }

    public List<User> getStudents() {
        return students;
    }

    public void setStudents(List<User> students) {
        this.students = students;
    }

    public Course(int id, String name) {
        this.id = id;
        this.name = name;
        this.subjects = subjects;
        this.teachers = teachers;
        this.students = students;
        this.listOfStudentss = listOfStudentss;
    }

    @Override
    public String toString() {
        return (" id: "+id+" name: " + name + "\n");
    }


    }

类(class)学生

import java.io.Serializable;

public class Student extends User implements Serializable {
   String name;
   String surname;
   String group;

   public String getName() {
       return name;
   }

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

   public String getSurname() {
       return surname;
   }

   public void setSurname(String surname) {
       this.surname = surname;
   }

   public String getGroup() {
       return group;
   }

   public void setGroup(String group) {
       this.group = group;
   }

       public Student(int id, String login, String password, String name, String surname, String group) {
       super(id, login, password);
       this.name = name;
       this.surname = surname;
       this.group = group;
   }


   @Override
   public String getUserData() {
       return null;
   }
   public String toString() {
       return (" id: "+id+" login: " + login + " password: " + password+" name: "+name+" surname: "+surname+" group: "+group+"\n");
   }

}

 List<Admin> listOfAdmins = new ArrayList<Admin>();
       List<Student> listOfStudents = new ArrayList<Student>();
       List<Teacher> listOfTeachers = new ArrayList<Teacher>();
       List<Subject> listofSubjects = new ArrayList<Subject>();
       List<Course> listofCourses = new ArrayList<Course>();

       Scanner scan222 = new Scanner(System.in);
       System.out.print(" ENTER ID OF COURSE: ");
       listofCourses.forEach(System.out::print);
       int idCourse = scan222.nextInt();
       for (int i = 0; i < listofCourses.size(); i++) {
           if (listOfCourses.get(i).getId()==(idCourse)) {
                       System.out.print(" ENTER ID OF STUDENT: ");
                       listOfStudents.forEach(System.out::print);
                       int studentID = scan222.nextInt();
                       for (int j=0; j<listOfStudents.size(); j++)
                           if (listOfStudents.get(j).getId()==(studentID))  {
 //error in this line                          listofCourses.get(idCourse).listOfStudentss.add(listOfStudents.get(studentID));
                               }
                                 }
                           }
                           listofCourses.get(idCourse).listOfStudentss.forEach(System.out::print);
                           listofCourses.forEach(System.out::print);

线程“main”中出现异常 java.lang.IndexOutOfBoundsException:索引 1 超出长度 1 的范围 在 java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64) 在 java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70) 在 java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248) 在 java.base/java.util.Objects.checkIndex(Objects.java:372) 在 java.base/java.util.ArrayList.get(ArrayList.java:458) 在 RemR.main(RemR.java:93)

Answer 1

您正在混淆两个不同的东西:类(class) ID 及其在 listOfCourses 列表中的索引。

据推测，您已为第一门类(class)指定了 id“1”，但其在 listOfCourses 列表中的索引为“0”。该错误告诉您，您正在向 listOfCourses 对象询问索引“1”处的对象(这是第二个对象，因为 java 从 0 开始计数)，但列表仅包含单个对象，因此会发生异常.