Question

这是我的学生课程，它创建一个具有姓名，成绩和身份证号码的学生。 Student用作TreeMap中的键，而学生的成绩用作值。当我实现Comparable时，我写了compareTo，但是在输入第一个学生时会弹出这个错误：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at Student.<init>(Student.java:25)
    at Main.main(Main.java:50)
Java Result: 1

我认为它来自于将学生的名字拆分为String []，但我已经测试了那些调用名字和姓氏的行，以及分割名称的行，它们似乎都是按预期工作，除非在compareTo中调用它们。

非常感谢任何帮助。

public class Student implements Comparable<Student>{
    private String name, grade, first, last;
    private String[] stuName;
    private int id;

    /**
     * Constructs a new Student with a name, ID Number, and a grade.
     * @param n name
     * @param i ID Number
     * @param g grade
     */
    public Student(String n, int i, String g){
        name = n;
        id = i;
        grade = g;
        stuName = n.split(" ");
        first = stuName[0];
        last = stuName[1];
    }

    /**
     * Compares Students. First by last name, then by first if the last names
     * are the same.  If the first names are also the same, the students are
     * compared by their ID Numbers.
     * @return the value upon comparing the proper property of the Student
     */
    @Override
    public int compareTo(Student other){
        if (last.equals(other.getLast())){
            if (first.equals(other.getFirst())){
                return id - other.getID();
            }else
                return first.compareTo(other.getFirst());
        }
        return last.compareTo(other.getLast());
    }

    /**
     * Changes the student's current grade.
     * @param g new grade
     */
    public void changeGrade(String g){
        grade = g;
    }

    /**
     * Returns student's name.
     * @return name
     */
    public String getName(){
        return name;
    }

    /**
     * Returns student's first name.
     * @return first name
     */
    public String getFirst(){
        return first;
    }

    /**
     * Returns student's last name.
     * @return last name
     */
    public String getLast(){
        return last;
    }

    /**
     * Returns the student's grade.
     * @return grade
     */
    public String getGrade(){
        return grade;
    }

    /**
     * Returns the student's ID Number
     * @return id number
     */
    public int getID(){
        return id;
    }

测试仪：

public class Main {
    public static void main(String[] args) throws InterruptedException{
        Map<Student, String> students = new TreeMap();
        Scanner in = new Scanner(System.in);
        System.out.println("How many students do you want to add?");
        int numStudents = in.nextInt();
        String name, grade;
        int id;


        for (int i = 1; i < numStudents; i++){
            System.out.println("Name of student " + i + "?");
            name = in.nextLine();
            in.nextLine();

            System.out.println("Grade of " + i + "?");
            grade = in.nextLine();

            System.out.println("ID Number of " + i + "?");
            id = in.nextInt();

            Student s = new Student(name, id, grade);
            students.put(s, s.getGrade());
        }


        System.out.println("How many students do want to remove");
        int remStudents = in.nextInt();

        for (int i = 0; i < remStudents; i++){
            System.out.println("ID?");
            int remID = in.nextInt();

            for (Student s : students.keySet()){
                if (s.getID() == remID){
                    students.remove(s);
                }
            }
        }


        System.out.println("How many grades do you want to change?");
        int changeGrades = in.nextInt();

        for (int i = 0; i < changeGrades; i++){
            System.out.println("ID?");
            int foo = in.nextInt();
            System.out.println("New grade?");
            String newGrade = in.nextLine();

            for (Student s : students.keySet()){
                if (s.getID() == foo){
                    s.changeGrade(newGrade);
                }
            }
        }

        String printout = "";
        for (Student s : students.keySet()){
            printout += s.getLast() + ", " + s.getFirst() + " (" + s.getID() + "): " + s.getGrade() + "\n";
        }
        System.out.println(printout);
    }
}

Answer 1

可能是因为你有两个不同的循环，有不同的索引：

在你的一个循环中，你从1开始，因此你只有1个学生：

for (int i = 1; i < numStudents; i++){

在删除循环中，您有一个从0开始的索引：

for (int i = 0; i < remStudents; i++){

我怀疑，你认为你添加了两个学生，但实际上你只有一个（在索引0处），因此你的indexout-of-bounds异常。

编辑，OP已为该例外添加了一个“完整”堆栈，上述答案与OP的问题无关.......

答案2：根据您修改的堆栈/异常编辑，唯一可能的答案是学生的名字中没有空格.....你的断言总是有空间根本就不是真的....

您可能想要在分组中添加count qualifiewr，以便在任何无效输入上获得空字符串：

stuName = n.split(" ", 2);

为什么这个数组不一致地超出界限？

1 个答案: