NullPointerException On a Calling a Function

I'm building a program that gets the value of a TextField, concatenate with some other Strings and then display them on a TextBox when the ScreenCommand is clicked, the problem is that it's calling a NullPointerException. My code is like this(of course it has a lot more stuff):

/* .... */
        } else if (command == submitCommand) {
            FirstPart();
            // write pre-action user code here
            switchDisplayable(null, getTextBox3());
            // write post-action user code here
        }
/* .... */

public void FirstPart() {
    String test = null;
    test = "tst" + textField.getString() + "test";
    textBox3.setString(test);
}
/* .... */

And I get this when I click the开发者_如何学C menu:

TRACE: <at java.lang.NullPointerException:   0>, Exception caught in Display class
java.lang.NullPointerException:   0
        at mp.releaser.MPReleaser.FirstPart(MPReleaser.java:535)
        at mp.releaser.MPReleaser.commandAction(MPReleaser.java:128)
        at javax.microedition.lcdui.Display$ChameleonTunnel.callScreenListener(), bci=46
        at com.sun.midp.chameleon.layers.SoftButtonLayer.processCommand(), bci=74
        at com.sun.midp.chameleon.layers.SoftButtonLayer.commandSelected(), bci=11
        at com.sun.midp.chameleon.layers.MenuLayer.pointerInput(), bci=188
        at com.sun.midp.chameleon.CWindow.pointerInput(), bci=88
        at javax.microedition.lcdui.Display$DisplayEventConsumerImpl.handlePointerEvent(), bci=19
        at com.sun.midp.lcdui.DisplayEventListener.process(), bci=296
        at com.sun.midp.events.EventQueue.run(), bci=179
        at java.lang.Thread.run(Thread.java:680)

What should I do to correct this?

PS: Netbeans should have a NullPointerException corrector tool :P

Looking at the FirstPart method, the only thing I can imagine is that textField is null or textBox3 is null. Are you sure it isn't null?

If I'm completely missing the point of your question, I apologize.

EDIT: Thank you, StriplingWarrior!

The only place a NullPointer can occur here is textField.getString() method or textBox3. Debug there.