ArrayList OutOfBounds - Java (Android) programming

Question

The error from the LogCat output is pointing to line 37 of QuestionView.java which I will comment into the code below. Below I have 4 snippets of 4 classes. Also I have the output from the LogCat.

MainMenu.java

public class MainMenu extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.mainmenumain);

    Button button1 = (Button)findViewById(R.id.startBtn);
    Button button2 = (Button)findViewById(R.id.categoriesBtn);
    Button button3 = (Button)findViewById(R.id.highscoresBtn);
    Button button4 = (Button)findViewById(R.id.aboutBtn);

    button1.setOnClickListener(new OnClickListener() {   
        public void onClick(View arg0) {
            Intent intent1 = new Intent(MainMenu.this, QuestionView.class);
            startActivity(intent1);  
        }
    });
//more code...

Question.java

public class Question {
String a1;
String a2;
String a3;
String a4;
int correctAnswer;
String query;

public Question() {
}

public Question(String a1, String a2, String a3, String a4, int correctAnswer, String query) {
    this.a1 = a1;
    this.a2 = a2;
    this.a3 = a3;
    this.a4 = a4;
    this.correctAnswer = correctAnswer;
    this.query = query;        
}

public String getA1() { return a1; }
public String getA2() { return a2; }
public String getA3() { return a3; }
public String getA4() { return a4; }
public String getQuery() { return query; }
public int getCorrectAnswer() { return correctAnswer; }
  }

Quiz.java

public class Quiz {
ArrayList<Question> qList = new ArrayList<Question>();
public static ArrayList<Question> tenQs = new ArrayList<Question>(10);

public Quiz() {
    qList.add(new Question("A", "B", "C", "D", 3, "Question 1?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 2?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 3?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 4?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 5?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 6?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 7?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 8?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 9?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 10?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 11?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 12?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 13?"));
    qList.add(new Question("A", "B", "C", "D", 3, "Question 14?"));
}

public void getRandom10() {
    for(int i = 0; i < 10; i++) {
        Question x = qList.get((int) Math.floor((qList.size()+1)*Math.random()));
        if(tenQs.contains(x) == true) {
            i--;
        } else {
            tenQs.add(x);
        }
    }
}

public ArrayList<Question> getTenQs() { 
    return tenQs;
}
  }

QuestionView.java

public class QuestionView extends Activity {

Quiz quiz = new Quiz();
ArrayList<Question> queries = quiz.getTenQs();

int correctAnswers = 0;
int wrongAnswers = 0;

int answer = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.questionviewmain);

    TextView question = (TextView)findViewById(R.id.question);

    Button answer1 = (Button)findViewById(R.id.answer1);
    Button answer2 = (Button)findViewById(R.id.answer2);
    Button answer3 = (Button)findViewById(R.id.answer3);
    Button answer4 = (Button)findViewById(R.id.answer4);

    for(int i = 0; i < 10; i++) {
        question.setText(queries.get(i).getQuery());  //Error points to here.
        answer1.setText(queries.get(i).getA1());
        answer2.setText(queries.get(i).getA2());
        answer3.setText(queries.get(i).getA3());
        answer4.setText(queries.get(i).getA4());

        answer = queries.get(i).getCorrectAnswer();

        answer1.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {
                if(answer == 0) {
                    correctAnswers++;
                } else {
                    wrongAnswers++;
                }
            }
        });
//more code...

LogCat

11-12 00:08:40.983: E/AndroidRuntime(4338): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.QuestionView}: java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.os.Looper.loop(Looper.java:137)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread.main(ActivityThread.java:4745)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at java.lang.reflect.Method.invokeNative(Native Method)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at java.lang.reflect.Method.invoke(Method.java:511)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at dalvik.system.NativeStart.main(Native Method)
11-12 00:08:40.983: E/AndroidRuntime(4338): Caused by: java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
11-12 00:08:40.983: E/AndroidRuntime(4338):     at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at java.util.ArrayList.get(ArrayList.java:304)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at com.example.test.QuestionView.onCreate(QuestionView.java:37)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.Activity.performCreate(Activity.java:5008)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
11-12 00:08:40.983: E/AndroidRuntime(4338):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)

Any help or input is appreciated! Thank you in advance.

Answer 1

You don't call your getRandom10() method to initialize list.

EDIT
Also you used bad design with class Quiz:

1. tenQs is static list that you fill with data from non-static list qList.

2. also tenQs is public that gives possibility to access it directly through class: Quiz.tenQs. I suppose to make it private and non-static and call getRandom10 inside consturtor to be sure of correct initialization of your Quiz.

3. get your random index as:

Code:

Random r = new Random();
for(int i = 0; i < 10; i++) {
    Question x = qList.get(r.nextInt(qList.size()));
    tenQs.add(x);
}

I understood. If you use inside for condition < tenQs.size() this for will not be executed cause actual size of tenQs is 0 but capacity is 10. So you must create constant with number of questions in quiz and use it in this for loop.

Answer 2

qList.size()+1 = 11 so random will give any number between 0 to 10... So it is fine if number is from 0 to 9, but 10 will cause your program to fail....

Answer 3

Change your for loop condition as:

for(int i = 0; i < queries.size() ; i++)

and make sure you are initialize queries ArrayList before using it