ErrorReport

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;


public class KBowlChallenge implements ActionListener{


    JButton startBtn = new JButton("Start");
    JButton answerBtn = new JButton("Answer");
    JButton nextBtn = new JButton("Next");

    TextArea questionTA = new TextArea("Welcome to the challenge Mode", 4,30, TextArea.SCROLLBARS_VERTICAL_ONLY);

    TextField answerTF = new TextField(10);
    TextField responseTF = new TextField(10);
    TextField rightTF =new TextField("0", 2);
    TextField wrongTF = new TextField("0", 2);
    TextField scoreTF = new TextField(3);

    int numRight = 0;
    int numWrong = 0;
    int questionNumber = 0;

    static QuestionAnswer[] questAns = new QuestionAnswer[60];

    @SuppressWarnings("unused")
    public static void main(String[] args){
        KBowlOpps.fillArrays();
        for(int i=0;i<questAns.length;i++){
            questAns[i] = new QuestionAnswer();
        }
        KBowlChallenge k = new KBowlChallenge();
    }

    public KBowlChallenge(){
        JFrame w = new JFrame();
        JPanel p = new JPanel();

        JLabel scoreLbl= new JLabel("Score: ");
        JLabel rightLbl = new JLabel("Correct: ");
        JLabel wrongLbl = new JLabel("Wrong: ");

        w.setSize(300,350);
        w.setTitle("Challenge Mode");
        w.setLocationRelativeTo(null);
        w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        w.setVisible(true);

        p.setLayout(new FlowLayout());
        p.add(startBtn);
            startBtn.addActionListener(this);
        //p.add(Box.createHorizontalStrut(80));
        //break
        p.add(questionTA);
            questionTA.setEditable(false);
        //p.add(Box.createHorizontalStrut(80));
        //break
        p.add(answerTF);
        //p.add(Box.createHorizontalStrut(90));
        //break
        p.add(answerBtn);
            answerBtn.addActionListener(this);
        p.add(Box.createHorizontalStrut(60));
        p.add(responseTF);
        p.add(nextBtn);
            nextBtn.addActionListener(this);
        p.add(Box.createHorizontalStrut(50));
        //break
        p.add(scoreLbl);
        p.add(scoreTF);
        p.add(rightLbl);
        p.add(rightTF);
        p.add(wrongLbl);
        p.add(wrongTF);
        w.add(p);

    }


    public void actionPerformed(ActionEvent e){

        if(e.getSource() == this.startBtn){
            questionTA.setText("");
            questionTA.append(questAns[questionNumber].getQuestion());
            System.out.print("Test");
            questAns = KBowlOpps.getChallengeQuestions();
        }
        if(e.getSource() == this.nextBtn){
            questionNumber++;
            questionTA.setText("");
            answerTF.setText("");
            questionTA.append(questAns[questionNumber].getQuestion());
        }
        if(e.getSource() == this.answerBtn){
            String answer = questAns[questionNumber].getAnswer();
            String input = answerTF.getText();
            System.out.println(answer);
            System.out.println(answerTF.getText());
            if(answer == input){
                responseTF.setText("Correct!");
                numRight++;
            }else{
                responseTF.setText("Incorrect!");
                numWrong++;
            }
            rightTF.setText(numRight+"");
            wrongTF.setText(numWrong+"");
        }


    }

}

============================================================================================
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: null string
    at sun.awt.windows.WTextAreaPeer.insertText(Native Method)
    at sun.awt.windows.WTextAreaPeer.insert(Unknown Source)
    at java.awt.TextArea.insertText(Unknown Source)
    at java.awt.TextArea.appendText(Unknown Source)
    at java.awt.TextArea.append(Unknown Source)
    at KBowlChallenge.actionPerformed(KBowlChallenge.java:86)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(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.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.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)