GradeBook class

Question

I am creating a void method which accepts nams and grades from 1 to 20 students. The condition is that this should stop when the user is finished or when the array is full. I need to validate the grades to be only A, B, C, D, OR F
When I made the condition it shows me an error:
exception in thread "main" java.lang NullPointerException
at GradeBook.input(GradeBook.java:29)
at Program4.main(Program4.java:8)
my methods is as follow:
public void input()
final String LIMIT = "QUIT";
int index = 0;
System.out.println("\nPlease enter grades and names (Enter QUIT to stop). ");
System.out.println("\nStudent # " index " :");
names[index] = Keyboard.readString();
index++;
while (!(names[index].equals(LIMIT)))
count++;
System.out.print("Exam Score: ");
grades[index] = Keyboard.readChar();
while((grades[index] < 'A') && (grades[index] > 'D')||(grades[index]!=('F')))
System.out.println("\nINVALIDE GRADE. PLEASE REENTER. ");
grades[index] = Keyboard.readChar();
System.out.println("\nStudent # " index " : ");
names[index] = Keyboard.readString();
names[index] = names[index].toUpperCase();
index++;
Cold you help me to see the errors...?

Answer 1

Hi
Why do i get this error when trying to run a code like
this:By 'run' I assume you mean you are entering a command like "java App" and you get the error. That's because the code you posted does not include a "public static void main(String[] args)" method. A class must contain this method to be launched as an application using the java command. The code you posted is an Applet, normally run using a web browser and HTML code.