我被要求创建一个具有以下规范的java OOP程序：
学生成绩名称：字符串ID： 字符串数学成绩：双英语成绩： 双重科学等级：双倍平均（）： double printInfo（）：void
说明是：
1）创建学生成绩等级
2）创建一个10学生的数组
3）使用键盘输入成绩信息
4）打印学生名单（姓名和平均数）
我的问题是每次运行公共课 Exception in thread "main" java.lang.NullPointerException
at javaDay3.StudentGradeApp2.main(StudentGradeApp2.java:15)
时，它总是给我这个错误
public static void printTheStudentDetails (StudentGrade info) {
现在我不知道该放在这个部分：
StudentGrade我的代码是：
package javaDay3;
public class StudentGrade {
String name;
String id;
double mathgrade;
double enggrade;
double scigrade;
public void printInfo() {
System.out.println("Math = " + mathgrade);
System.out.println("English = " + enggrade);
System.out.println("Science = " + scigrade);
System.out.println( "Average = " + average());
}
public double average () {
return ((mathgrade + enggrade + scigrade) / 3);
}
public void printCompleteInformation() {
System.out.println("Name = " + name);
System.out.println("ID = " + id);
System.out.println("Math = " + mathgrade);
System.out.println("English = " + enggrade);
System.out.println("Science = " + scigrade);
System.out.println( "Average = " + average());
}
public void printNeed () {
System.out.println("Name = " + name);
System.out.println( "Average = " + average());
}
}
班级：
package javaDay3;
import java.util.Scanner;
public class StudentGradeApp {
public static void main(String[] args) {
// TODO Auto-generated method stub
StudentGrade stud1 = new StudentGrade ();
stud1.name = "SpongeBop SquarePants";
stud1.id = ("Student 1");
stud1.mathgrade = 72;
stud1.enggrade = 80;
stud1.scigrade = 90;
stud1.average();
StudentGrade stud2 = new StudentGrade ();
stud2.name = "Patrick Star";
stud2.id = ("Student 2 ");
stud2.mathgrade = 72;
stud2.enggrade = 85;
stud2.scigrade = 91;
stud2.average();
StudentGrade stud3 = new StudentGrade ();
stud3.name = "Squidward Tentacles";
stud3.id = ("Student 3" );
stud3.mathgrade = 90;
stud3.enggrade = 85;
stud3.scigrade = 95;
stud2.average();
StudentGrade stud4 = new StudentGrade ();
stud4.name = "Eugene H. Krabs";
stud4.id = ("Student 4");
stud4.mathgrade = 95;
stud4.enggrade = 85;
stud4.scigrade = 95;
stud4.average();
StudentGrade stud5 = new StudentGrade ();
stud5.name = "Sandy Cheeks";
stud5.id = ("Student 5");
stud5.mathgrade = 75;
stud5.enggrade = 75;
stud5.scigrade = 95;
stud5.average();
StudentGrade stud6 = new StudentGrade ();
stud6.name = "Gary the Snail";
stud6.id = ("Student 6");
stud6.mathgrade = 75;
stud6.enggrade = 74;
stud6.scigrade = 95;
stud6.average();
StudentGrade stud7 = new StudentGrade ();
stud7.name = "Sheldon J Plankton";
stud7.id = ("Student 7 ");
stud7.mathgrade = 79;
stud7.enggrade = 76;
stud7.scigrade = 75;
stud7.average();
StudentGrade stud8 = new StudentGrade ();
stud8.name = "Larry The Lobster";
stud8.id = ("Student 8");
stud8.mathgrade = 79;
stud8.enggrade = 76;
stud8.scigrade = 75;
stud8.average();
StudentGrade stud9 = new StudentGrade ();
stud9.name = "King Neptune";
stud9.id = ("Student 9 ");
stud9.mathgrade = 79;
stud9.enggrade = 96;
stud9.scigrade = 75;
stud9.average();
StudentGrade stud10 = new StudentGrade ();
stud10.name = "Pearl Krabs";
stud10.id = ("Student 10 ");
stud10.mathgrade = 79;
stud10.enggrade = 76;
stud10.scigrade = 75;
stud10.average();
/*stud1.printInfo();
System.out.println(" ");
stud2.printInfo();
System.out.println(" ");
stud3.printInfo();
System.out.println(" ");
stud4.printInfo();
System.out.println(" ");
stud5.printInfo();
System.out.println(" ");
stud3.printInfo();
System.out.println(" ");
stud6.printInfo();
System.out.println(" ");
stud7.printInfo();
System.out.println(" ");
stud8.printInfo();
System.out.println(" ");
stud9.printInfo();
System.out.println(" ");
stud10.printInfo(); */
}
public static void printTheStudentDetails (StudentGrade info) {
}
}
StudentGradeApp课程：
StudentGradeApp2 import java.util.Scanner;
public class StudentGradeApp2 {
public static void main(String[] args) {
// TODO Auto-generated method stub
StudentGrade studgrad [] = new StudentGrade [10];
Scanner scanner = new Scanner (System.in);
for(int i = 0; i <= studgrad.length; i++) {
System.out.print("Enter Math Grade = ");
studgrad[i].mathgrade = scanner.nextInt();
System.out.print("Enter English Grade = ");
studgrad[i].enggrade = scanner.nextInt();
System.out.print("Enter Science Grade = ");
studgrad[i].scigrade = scanner.nextInt();
}
for(StudentGrade info:studgrad)
info.printInfo();
scanner.close();
}
}
上课：
Hibernate答案 0 :(得分：2)
java.lang.NullPointerException的已发布代码存在以下问题：
studgrad[i].mathgrade获得null.mathgrade。它相当于调用mathgrade, enggrade, scigrade。StudentGrade scanner.nextInt()中的For loop condition是双倍的，您正在使用package javaDay3;
import java.util.Scanner;
public class StudentGradeApp2 {
public static void main(String[] args) {
// TODO Auto-generated method stub
StudentGrade studgrad[] = new StudentGrade[10];
Scanner scanner = new Scanner(System.in);
for (int i = 0; i < studgrad.length; i++) {
StudentGrade sg = new StudentGrade();
System.out.print("Enter Math Grade = ");
sg.mathgrade = Double.parseDouble(scanner.nextLine());
System.out.print("Enter English Grade = ");
sg.enggrade = Double.parseDouble(scanner.nextLine());
System.out.print("Enter Science Grade = ");
sg.scigrade = Double.parseDouble(scanner.nextLine());
studgrad[i] = sg;
}
for (StudentGrade info : studgrad)
info.printInfo();
scanner.close();
}
}
between不正确PFB更正实施：
\DateTime答案 1 :(得分：1)
现在我不知道该放在这个部分：
public static void printTheStudentDetails（StudentGrade info）{
您需要一个列表来添加所有学生成绩
org.hibernate.QueryException:
could not resolve property: pet.name of: Hero
每次创建新的StudentGrade对象时，都会将其添加到列表中。
在StudentGrade课程中override List<> studentList = new ArrayList<StudentGrade>();
studentList.add(stud1);
studentList.add(stud2);
方法
现在，在您的方法中，printTheStudentDetails传递学生列表toString()
studentList答案 2 :(得分：0)
调试您遇到问题的代码。你会发现你的对象是null。不要忘记将数据添加到列表中，以便可以使用它们。