私のエラーである私は、文字列、整数、または変数

Question

これらから特定の配列を作成する方法を見つけ出すことはできません：私は3つの等級（最後の3の配列を持っているので、問題があることを理解して

Exception in thread "main" java.lang.NullPointerException 
at Student.<init>(Student.java:22) 
at Roster.<init>(Roster.java:35) 
at Roster.main(Roster.java:15)) 

生徒名の列に）正しく格納されていません。

import java.util.*; 
import java.lang.*; 
public class Roster 
{ 
    static String[] students = {"1,John,Smith,John1989@gmail.com,20,88,79,59", 
           "2,Suzan,Erickson,Erickson_1990@gmailcom,19,91,72,85", 
           "3,Jack,Napoli,The_lawyer99yahoo.com,19,85,84,87", 
           "4,Erin,Black,Erin.black@comcast.net,22,91,98,82", 
           "5,Michael,Brauer,mbrauer@wgu.edu,30,99,98,96"}; 

    static ArrayList<Student> myStudents = new ArrayList<Student>(); 

    public static void main(String[] args) 
    { 
     new Roster(); 
    } 

    public Roster() 
    { 
     for (int i = 0; i < students.length; i++) 
     { 
      String y = students[i]; 
      String[] variable = y.split(","); 

      String id = variable[0]; 
      String first = variable[1]; 
      String last = variable[2]; 
      String email = variable[3];    
      int age = Integer.parseInt(variable[4]); 
      int grade1 = Integer.parseInt(variable[5]); 
      int grade2 = Integer.parseInt(variable[6]); 
      int grade3 = Integer.parseInt(variable[7]); 
      int[] grades = new int[]{grade1, grade2, grade3}; 

      //Here is the first issue that I am having: Nothing stores to grades. 

      Student x = new Student(id, first, last, email, age, grades); 

      myStudents.add(x); 
     } 

     print_all(); 

     print_invalid_emails(); 
     for (Student y : myStudents) 
     { 
      print_average_grade(y.getId()); 
     } 
    } 

    public static void print_all() 
    { 
     for (Student x : myStudents) 
     { 
      System.out.println(x); 
     } 
    } 

    public static void print_invalid_emails() 
    { 
     for (Student x : myStudents) 
     { 
      String email = x.getEmail(); 
      if (!email.contains("@")) 
      { 
       System.out.println("INVALID EMAIL: " + email); 
      } 
      else if (!email.contains(".")) 
      { 
       System.out.println("INVALID EMAIL: " + email); 
      } 
      else if((email.contains(" "))) 
      { 
       System.out.println("INVALID EMAIL: " + email); 
      } 
     } 

     remove("3"); 
     remove("3"); 
    } 

    public static void remove(String id) 
    { 
     for (int i = 0; i < myStudents.size(); i++) 
     { 
      if (myStudents.get(i).getId().equals(id)) 
      { 
       myStudents.remove(i); 
       System.out.println("STUDENT ID: (" + id + ") *NOT FOUND*"); 
       return; 
      } 
     } 
     System.out.println("STUDENT ID: (" + id + ") !DELETED!"); 
    } 

    public static void print_average_grade(String id) 
    { 
     for (Student y : myStudents) 
     { 
      if(y.getId().equals(id)) 
      { 
       double total = 100; 
       double average = total/3; 
       System.out.println("STUDENT ID: (" + id + ") " + average); 
      } 
     } 
    } 
} 

public class Student 
{ 
    String id; 
    String first; 
    String last; 
    String email; 
    int age; 
    int[] grades; 

    public Student(String id, String first, String last, String email, int age, int[] grades) 
    { 
     this.id = id; 
     this.first = first; 
     this.last = last; 
     this.email = email; 
     this.age = age; 
     this.grades = grades; 
    } 

    //This is the other problem. I am trying to make an array 

    public int[] gradeArray = {grades[1], grades[2], grades[3]}; 

    public String getFirst() 
    { 
     return first; 
    } 
    public void setFirst(String first) 
    { 
     this.first = first; 
    } 
    public String getLast() 
    { 
     return last; 
    } 
    public void setLast(String last) 
    { 
     this.last = last; 
    } 
    public String getEmail() 
    { 
     return email; 
    } 
    public void setEmail(String email) 
    { 
     this.email = email; 
    } 
    public int getAge() 
    { 
     return age; 
    } 
    public void setAge(int age) 
    { 
     this.age=age; 
    } 
    public String getId() 
    { 
     return id; 
    } 
    public void setId(String id) 
    { 
     this.id = id; 
    } 
    public int[] getGradeArray() 
    { 
     return gradeArray; 
    } 
    public void myGrades(int[] grades) 
    { 
     this.grades = grades; 
    } 
    //Print to output 
    public String toString() 
    { 
     return "STUDENT: ID-" + id + " AGE-" + age + " NAME-" + last + ", " + first; 
    } 
} 

Answer 1

ここでは、（0ベース）int配列に3つの等級を保存している：[3]の範囲を超えている

int[] grades = new int[]{grade1, grade2, grade3}; 

しかし、その後、あなたが成績にアクセスしようとしていますアレイ。

public int[] gradeArray = {grades[1], grades[2], grades[3]}; 

Erickson_1990 @ gmailcomは有効なメールテストに失敗します。それがテストの理由で意図的であったのか、それとも誤植であるのかはわかりません。