從文件問題讀取數據（Java初學者語言）

Question

夥計們我從讀取文件中的數據時遇到問題。

當我試圖從文件輸入後計算GPA時，我只能得到名稱和ID的權利。檢查全碼here

Name: Ali Ahmad 
ID: 2009000 

Exception in thread "main" java.lang.NullPointerException 
    at IcsProject.display(IcsProject.java:136) 
    at IcsProject.main(IcsProject.java:45) 

`

我真的需要這方面的幫助。我花了幾個小時來修復它，但我不能。

public static void readFromFile() throws IOException 
{ 
    System.out.println("Enter the file name "); 
     String FileNameInput = keyboard.next(); 
     Scanner filein = new Scanner(new FileInputStream(FileNameInput)); 


     stuName = filein.nextLine(); 
     ID = filein.nextInt(); 

     filein.next(); 
     semNum = filein.nextInt(); 


    courseCode=new String[semNum][]; 
    creditHours=new int[semNum][]; 
    grade=new String[semNum][]; 
    semCode=new int[semNum]; 

    for(int i = 0; i < semNum; i++) 
    { 
      semCode[i] = filein.nextInt(); 

      filein.next(); 
      semCourses = filein.nextInt(); 

      for(int j = 0; j < semCourses; j++) 
      { 
       courseCode[i][j]=filein.next(); 
       creditHours[i][j]=filein.nextInt(); 
       grade[i][j]=filein.next(); 
      } 
      } 
    } 

輸入數據是這樣的：

Ali Ahmad 
2009000 
Semesters 2 

093 
Courses 2 

IAS100 2 A+ 
PE100 2 B 

101 
Courses 4 

ICS103 3 A+ 
MATH101 4 B 
PHYS101 4 C+ 
CHEM101 4 D+ 

這是該方法計算GPA等能正常工作，手動輸入。

public static void display(PrintWriter output) 
{ 
output.println("Name: "+stuName); 
output.println("ID: "+ID); 
output.println(""); 

GPA=new double[semNum]; 
for(int i=0;i<semNum;i++) 
{ 
GPA[i]=0.0; 
double creditHoursSum=0.0; 
for(int j=0;j<courseCode[i].length;j++) 
{ 
    GPA[i]+=creditHours[i][j]*gradeValue(grade[i][j]); 
    creditHoursSum+=creditHours[i][j]; 
} 
GPA[i]=GPA[i]/creditHoursSum; 
} 
cumulativeGPA=0.0; 
for(int i=0;i<semNum;i++) 
cumulativeGPA+=GPA[i]; 
cumulativeGPA=cumulativeGPA/semNum; 
for(int i=0 ; i < semNum ; i++) 
output.printf("GPA for semester %d = %.2f\t%s\n",semCode[i],GPA[i],gpaLvl(GPA[i]));//Using `Printf` To limit the number of digits of the GPA. I learned the method from our Course Book.Took me a while to get it though. 
output.printf("\nCumulative GPA = %.2f\n",cumulativeGPA); 
output.println(""); 
} 

Answer 1

您必須正確初始化「子」陣列，即你的i -loop內，但j前右-loop加上下面幾行：

courseCode[i] = new String[semCourses]; 
creditHours[i] = new int[semCourses]; 
grade[i] = new String[semCourses];