Question

So I have to write a program that is a flight reservation system. If I run the program normally and enter in values when prompted, nothing goes wrong, but when I use a .txt file input, I get a NullPointerException. The part of the code im getting the NullPointerException is

 public void instantiateAirplane() throws IOException{
        boolean creatingAirplane = true;
        String className= "";
        String seatFormat;
        int rowNums;
        while (creatingAirplane){
            input  = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("Enter service class name or [ENTER] to finish: ");

            className = input.readLine();
            if (className.equals("")) {
                creatingAirplane = false;
            }
            else{   
                System.out.println("Enter seating pattern: ");
                seatFormat = input.readLine();
                System.out.println("Enter number of rows: ");
                rowNums = Integer.parseInt(input.readLine());
                plane.creatSeatingChart(className, rowNums, seatFormat);
            }
        }
    }

When doing normal input, it runs like this:

C:\Users\Owner\Desktop\Math&CIS\CS151\HW1>java UserInterface planes
Enter service class name or [ENTER] to finish:
First Class
Enter seating pattern:
WAAW
Enter number of rows:
2
Enter service class name or [ENTER] to finish:
Business Class
Enter seating pattern:
WAAW
Enter number of rows:
2
Enter service class name or [ENTER] to finish:

Add [P]assenger, Add [G]roup, [C]ancel Reservations, Print [S]eating chart, Prin
t [M]anifest, [Q]uit

But when when using a .txt input, the following happens

C:\Users\Owner\Desktop\Math&CIS\CS151\HW1>java UserInterface planes < input.txt
Enter service class name or [ENTER] to finish:
Enter seating pattern:
Enter number of rows:
Enter service class name or [ENTER] to finish:
Exception in thread "main" java.lang.NullPointerException
        at UserInterface.instantiateAirplane(UserInterface.java:21)
        at UserInterface.main(UserInterface.java:123)

C:\Users\Owner\Desktop\Math&CIS\CS151\HW1>

the exception happens at the line “if (className.equals("")) {“

the input text is the follwing:

First
WAAW
2
Economy
WCAACW
3

...

I’m not sure why it doesn’t work when using an input text.

Answer 1

That readLine() method returns a null once the iterator reaches what is known as EOF or the end of file. Check to see if ClassName == null || className.Equal("")...

Also you may want to declare input = new BufferedReader(new InputStreamReader(System.in)); out side of your loop just so you are not re-initializing the reader at each loop iteration.

-!