Error in .getText() in a parseInt in Java

Question

I know the title might not be that helpful. I do apologize. My problem is that I am trying to create a simple MPG application to help me get used to GUI. I have a gallons and a miles JTextField. I also have an ueditable JTextField to display the MPG. I am trying to convert the user input to an integer then divide the gallons and miles input for the result of the miles per gallon, which will be displayed.

I have the parseInt as displayed below:

    int mil = Integer.parseInt(miles1.getText());
    int gal = Integer.parseInt(gallons1.getText());

then the MPG:

int mpg = gal / mil;

It shows no error in the code, but once I go to run the application I get these errors:

java.lang.NullPointerException
at app.<init>(app.java:40)
at app$1.run(app.java:26)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Does anybody know what is causing this?

You should probably show the code on or about line 40 of app.java, since that's where your NullPointerException occurs. — Samhain, Feb 17 '14 at 19:28
@Samhain line 40 is ` int mil = Integer.parseInt(miles1.getText());` — engz, Feb 17 '14 at 19:30
@user3320501 Then miles1 is null. You haven't initialized it yet. — Samhain, Feb 17 '14 at 19:35
@Samhain how exactly do you initialize it? I would like it to take the user input of the two JTextfields then display them in an uneditable JTextfield once a button is clicked. — engz, Feb 17 '14 at 19:37

score 0 · Answer 1 · answered Feb 17 '14 at 19:46

First of all u said that u have two textareas named gallons and miles but u used the identifiers gallons1 and miles1.

If thats not the case then, try initialising the gallons and miles jtextarea.

for e.g you may see something like these

    JTextArea gallons1;
    JTextArea miles1;

Try making them these respectively

    JTextArea gallons1=new JTextArea();
    JTextArea miles1=new JTextArea();

score 0 · Answer 2 · answered Feb 17 '14 at 19:49

It sounds like the issue is that the JTextFields are null when you are calling .getText(). Make sure that they have a value when doing the math on the fields and you will be fine.

If you want to avoid errors completely, use if (miles1.matches("[0-9]*) { logic } and it won't throw an error for the Integer.parseInt if it's input incorrectly (The regex will fail since it's non-numeric).

Error in .getText() in a parseInt in Java

2 Answers2