java - 相对于构造函数抛出越界运行时错误

Question

我立即收到源 self 的 Student 的运行时错误类构造函数。这是我知道的唯一错误，但是可能还有更多。

错误内容如下:

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

at java.util.ArrayList.rangeCheck(ArrayList.java:635)

at java.util.ArrayList.set(ArrayList.java:426)

at Student.(Student.java:11)

at TestStudent.main(TestStudent.java:5)

显示我的 IDE 中错误的图形:

这是更新后的功能代码:

import java.util.*;
public class Student {
    private String name;
    private ArrayList<Integer> quizList = new ArrayList<Integer>(5);
    public Student(String name, int qz1, int qz2, int qz3, int qz4, int qz5) {
        this.name = name;
        int qz[] = {qz1, qz2, qz3, qz4, qz5};
        for(int i = 0; i < qz.length; i++) {
            quizList.add(qz[i]);
        }
    }

    public String getName() {
        return name;
    }

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

    public ArrayList<Integer> getQuizList() {
        return quizList;
    }

    public int getQuiz(int location) {
        return quizList.get(location);
    }

    public void setQuiz(int location, int qz) {
        quizList.set(location, qz);
    }
}

import java.util.*;
public class TestStudent {
    public static void main(String [] args) {
        ArrayList<Student> list = new ArrayList<Student>();
        list.add(new Student("Mark Kennedy", 70, 80, 90, 100, 90));
        list.add(new Student("Max Gerard", 80, 85, 90, 85, 80));
        list.add(new Student("Jean Smith", 50, 79, 89, 99, 100));
        list.add(new Student("Betty Farm", 85, 80, 85, 88, 89));
        list.add(new Student("Dilbert Gamme", 70, 70, 90, 70, 80));

        printBook(list);
    }

    public static void printBook(ArrayList<Student> list) {
        for(Student token : list) {
            System.out.print(token.getName() + "\t");
            for(int i = 0; i < 5; i++) {
                System.out.printf("%5d\t", token.getQuiz(i));
            }
            System.out.println();
        }
    }

    public static void replaceName(ArrayList<Student> list, String find, String replace) {
        int position = 0;
        int values[] = new int[5];
        for(int i = 0; i < list.size(); i++) {
            values[i] = list.get(i).getQuiz(i);
        }
        for(int i = 0; i < list.size(); i++) {
            if (list.get(i).getName().equals(find)) {
                list.get(i).setName(replace);
            }
        }
    }

    public static void replaceQuiz(ArrayList<Student> list, String find, int quizNum, int replace) {
        for(int i = 0; i < list.size(); i++) {
            if (list.get(i).getName().equals(find)) {
               list.get(i).setQuiz((quizNum-1), replace);
            }
        }
    }

    public static void replaceStudent(ArrayList<Student> list, String find, Student replacement) {
        insertStudent(list, find, replacement.getName());
        deleteStudent(list, find);
    }

    public static void insertStudent(ArrayList<Student> list, String find, String name) {
        int position = 0;
        int values[] = new int[5];
        for(int i = 0; i < list.size(); i++) {
            values[i] = list.get(i).getQuiz(i);
        }
        for(int i = 0; i < list.size(); i++) {
            if(list.get(i).getName().equals(find)) {
                position = i;
            }
        }
        list.add(position, new Student(name, values[0], values[1], values[2], values[3], values[4]));
    }

    public static void deleteStudent(ArrayList<Student> list, String find) {
        int location = 0;
        int i;
        for(i = 0; i < list.size(); i++) {
            if (list.get(i).getName().equals(find)) {
                location = i;
                break;
            }
        }
        if (i != list.size()) {
            list.remove(location);
        }
    }
}

更新:

修改了Student中的一些代码:

    private String name;
    private ArrayList<Integer> quizList;
    public Student(String name, int qz1, int qz2, int qz3, int qz4, int qz5) {
        this.name = name;
        int qz[] = {qz1, qz2, qz3, qz4, qz5};
        for(int i = 0; i < qz.length; i++) {
            quizList.add(qz[i]);
        }
    }

现在抛出此错误:

java.lang.NullPointerException

at Student.(Student.java:9)

at TestStudent.main(TestStudent.java:5)

Answer 1

使用quizList.add(qz[i]);而不是quizList.set(i, qz[i]);当您想要将对象设置到特定位置时，您的列表为空。

documentation of set :

IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size())

您的更新:

您删除了行 quizList = new ArrayList<Integer>(5); 。它会初始化您的列表。您需要将此行固定到位，否则没有可以添加对象的列表。一个NullPointerException始终意味着当您想要读取/写入对象时尚未创建对象。