我有一个名为 sectionArray 的二维数组，它是 Student 类的类型。每个学生都有一个姓名和一个包含 5 个等级的数组 [] 用于考试成绩。这些名称和分数被分成文件中必须读取的部分。无论我改变什么，我都会在我的 sectionArray 上得到一个 nullPointer。感谢您的任何建议。
import java.util.*;
import java.io.*;
public class ProgressReport {
private Student[][] sectionArray;// each student has a name,
// grade, average,
// and the array of scores
private File file;
private Scanner inputFile;
public ProgressReport() throws IOException {
sectionArray = new Student[2][];
file = new File("Lab5A.in.txt");
inputFile = new Scanner(file);
}
/**
*
* @return the values in the sectionArray
*/
public Student[][] getSectionArray() {
return sectionArray;
}
/**
* initialize sectionArray and set the values
*
* @param sectionArray
* passed 2D array of Students
*/
public void setSectionArray(Student[][] sectionArray) {
for (int i = 0; i < sectionArray.length; i++) {
for (int j = 0; j < sectionArray[i].length; j++) {
this.sectionArray[i][j] = sectionArray[i][j];
}
}
}
/**
* reads from the file and creates new Students
*
* @throws IOException
*/
public void readInputFile() throws IOException {
int colNum = 0;
int section = 0;
String name = " ";
int[] grades = new int[5];
while (inputFile.hasNext()) {
colNum = inputFile.nextInt();// gets size of row
sectionArray[section] = new Student[colNum];// initialize array
// iterates through colNum amount of times
for (int j = 0; j < colNum; j++) {
name = inputFile.next();// gets next name in column
for (int i = 0; i < 5; i++) {
// stores scores for that name
grades[i] = inputFile.nextInt();
}
// creates new Student with name and grades
sectionArray[section][j] = new Student(name, grades);
section++;
}
}
// passes the values in sectionArray
setSectionArray(sectionArray);
}
}
我的学生班是这样的：
public class Student {
private String name = " "; // Store the name of the student
private char grade; // Store the letter grade
private double average; // Store the average score
private int[] scores; // Store the five exam scores
public Student() {
grade = ' ';
average = 0.0;
}
public Student(String name, int[] score) {
this.name = name;
scores = new int[5];
for (int i = 0; i < scores.length; i++) {
scores[i] = 0;
}
for (int i = 0; i < scores.length; i++) {
this.scores[i] = score[i];
}
}
// getters
public String getName() {
return name;
}
public char getGrade() {
return grade;
}
public double getAverage() {
return average;
}
// think about changing this to return a different format
public int[] getScores() {
return scores;
}
// setters
public void setScore(int[] scores) {
}
public void setName(String name) {
this.name = name;
}
public void setGrade(char grade) {
this.grade = grade;
}
public void setAverage(double average) {
this.average = average;
}
/**
* determine the average of the five test scores for each student
*/
public void calculateAverage() {
double total = 0;
double average = 0;
for (int i = 0; i < scores.length; i++) {
total += scores[i];
}
average = total / scores.length;
setAverage(average);
}
/**
* Determine the student's letter grade based on average of test scores
*/
public void calculateGrade() {
double average = 0;
average = getAverage();
if (average <= 100 && average >= 90) {
setGrade('A');
} else if (average <= 89 && average >= 80) {
setGrade('B');
} else if (average <= 79 && average >= 70) {
setGrade('C');
} else if (average <= 69 && average >= 60) {
setGrade('D');
} else if (average <= 59 && average >= 0) {
setGrade('F');
}
}
public String toString() {
return getName() + " " + getAverage() + " " + getGrade();
}
}