Why do I get a NullPointerException when using text input as opposed to user input?
<p>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 <code>NullPointerException</code>. The part of the code im getting the <code>NullPointerException</code> is </p>

<pre><code> 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);
            }
        }
    }
</code></pre>

<p>When doing normal input, it runs like this:</p>

<pre><code>C:\Users\Owner\Desktop\Math&amp;CIS\CS151\HW1&gt;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
</code></pre>

<p>But when when using a .txt input, the following happens </p>

<pre><code>C:\Users\Owner\Desktop\Math&amp;CIS\CS151\HW1&gt;java UserInterface planes &lt; 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&amp;CIS\CS151\HW1&gt;
</code></pre>

<p>the exception happens at the line "<code>if (className.equals("")) {</code>"</p>

<p>the input text is the follwing:</p>

<pre><code>First
WAAW
2
Economy
WCAACW
3

...
</code></pre>

<p>I'm not sure why it doesn't work when using an input text.</p>
