我创建了一个具有ID,GPA和Credits值的班级学生,然后在班级StudentList中创建了100个数组元素。当试图写入元素时,我得到NullPointerException。为什么在为对象设置值时收到NullPointerExceptions?
学生类:
package com.ahellhound.pkg202studentrecordproject;
public class Student {
private String studentID;
private double studentGPA;
private int creditHours;
public void Student() {}
public String getStudentID() {return studentID;}
public void setStudentID(String studentID) {this.studentID = studentID;}
public double getStudentGPA() {return studentGPA;}
public void setStudentGPA(double studentGPA) {this.studentGPA = studentGPA;}
public int getCreditHours() {return creditHours;}
public void setCreditHours(int creditHours) {this.creditHours = creditHours;}
/**
* @return StudentID, StudentGPA, StudentCreditHours separated by spaces
*/
@Override
public String toString() {
return String.format("%s %f.2 $d", studentID, studentGPA, creditHours);
}
}
然后在StudentList,我试图传递三个参数传递给它:
private Student[] studentArray = new Student[100];
private int counter = 0;
public String addStudentRecord(String studentID, double studentGPA, int studentCredits){
studentArray[counter].setStudentID(studentID);
studentArray[counter].setStudentGPA(studentGPA);
studentArray[counter].setCreditHours(studentCredits);
String arrayString = studentArray[counter].toString();
counter++;
return arrayString;
}