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Difference in size of reference variables in Java. (List vs ArrayList)

By : user2176464
Date : October 14 2020, 02:21 PM
To fix this issue All reference variables are of the same size, yes. This is addressed somewhat tangentially in the JVM specifiation in a couple of places: §2.2:
code :
List<String> list = new ArrayList<>();

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Can I assign Java values from an ArrayList to different variables without hardcoding the size?

By : user3537165
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The source of this is most certainly a bad code design. Also to what do you initialize the variable if the arraylist doesn't contain the field (after all you use it later)? A larger example or what exactly you're trying to do would help here. Usually just using
But I can think of at least two ways to do this:
code :
    switch(myArrayList.size()) {
    case 5:
        var4 = myArrayList.get(4);
    case 4:
        var3 = myArrayList.get(3);
    case 3:
        var2 = myArrayList.get(2);
            // and so on
    try {
        var0 = myArrayList.get(0);
        var1 = myArrayList.get(1);
    catch(IndexOutOfBoundsException ex){

Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference

By : virginiamurdoch
Date : March 29 2020, 07:55 AM
it helps some times I am getting two type of responses from the server the first one in case of the routes is being sent to the server with the JSOn string then I get as response {"status":230,"routes":[1,9,3]} or not being sent then I get {"status":201}. Currently the app crashes if the response is {"status":201} and I am getting: , It seems like routeList is equal to null
code :
final ArrayList<Integer> routeList = extras.getIntegerArrayList("stop_route");
int routeListSize = routeList.size(); // Crash

protected void onPostExecute(Void result) {
    // Intent with Conetxt of the Asyntask class and
    if(routes != null){
       Intent intent = new Intent(mContext, MainActivity.class);
       intent.putIntegerArrayListExtra("stop_route", routes);
       Log.e("123", "Avoiding null pointer, the routes are null!!!");

java.util.ArrayList.size()' on a null object reference

By : TriTai Huynh
Date : March 29 2020, 07:55 AM
wish help you to fix your issue Your problem is that (ArrayList) dataSnapshot.getValue() is sometimes null and after you store values, the exception is thrown in getItemCount. If you are ok with returning 0 as size when values is null, then the solution is
code :
public int getItemCount() {
    return (values == null) ? 0 : values.size();

Saving Fragment State gives error: int java.util.ArrayList.size()' on a null object reference

By : obo
Date : March 29 2020, 07:55 AM
help you fix your problem The main problem was that I had forgotten to add the super.onSaveInstanceState(...) method:
code :
protected void onSaveInstanceState(Bundle outState) {
    //this.getSupportFragmentManager().putFragment(outState, myFragment.TAG, myFragment);

easy java swing arrayList.size() error? constructor parameter override? arrayList.size() not working? java

By : Harish Reddy
Date : March 29 2020, 07:55 AM
hop of those help? You have five answers and questions at the very first time when executing your swing application in the main method. You can also see the output first and the last on your console as follows
code :
The Answer List Size = 1
The Question List Size = 1
The Answer List Size = 5
The Question List Size = 5
package justtest;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.Serializable;
import java.util.ArrayList;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.ScrollPaneConstants;

public class QuizCardTestDrive /*extends QuizCard*/ {

    public static void main(String[] args) {
        QuizCardBuilder qb = new QuizCardBuilder();

        QuizCard b5 = new QuizCard();
        System.out.println("The Answer List Size = " + b5.getAnswerListSize());
        System.out.println("The Question List Size = " + b5.getQuestionListSize());

        b5.setLists("is This a test?", "DUHH!!!");
        b5.setLists("adfadfad", "DUHH!!!");
        b5.setLists("adfadfad", "DUHH!!!");
        b5.setLists("adfadfad", "DUHH!!!");

        System.out.println("The Answer List Size = " + b5.getAnswerListSize());
        System.out.println("The Question List Size = " + b5.getQuestionListSize());



class QuizCard implements Serializable {
    private static final long serialVersionUID = 1L;
    private ArrayList<String> mQuestionList = new ArrayList<String>();
    private ArrayList<String> mAnswerList = new ArrayList<String>();

    //public QuizCard(String question, String answer) {
    //  mQuestionList.add(question);
    //  mAnswerList.add(answer);


    final static String firstQuestion = "What class is used for writing to a text file?";
    final static String firstAnswer = "class FileWriter";

    public QuizCard() {
        //mQuestionList.add(0, "What class is used for writing to a text file?");
        //mAnswerList.add(0,"class FileWriter");



    public void clearAnswers()

    public void clearQuestions()

    public void setLists(String q, String a) {


    public String getQuestion(int q) {

        //if ((q > mQuestionList.size())) {
        //  q = 0;

        //return mQuestionList.get(q);
        return mQuestionList.get(q);

    public String getAnswer(int a) 
        //if ((a > mAnswerList.size())) {
        //  a = 0;
        //return mAnswerList.get(a);

        return mAnswerList.get(a);

    public int getQuestionListSize() {
        return mQuestionList.size();

    public int getAnswerListSize() {
        return mAnswerList.size();


class QuizCardBuilder implements Serializable, ActionListener {
    private static final long serialVersionUID = 1L;
    //QuizCard b5 = new QuizCard();
    QuizCard qz;

    int list;
    JFrame frame;
    JPanel background;

    JTextArea areaN;
    JTextArea areaS;
    JButton buttonNext;
    JLabel labelN;
    JLabel labelS;
    JScrollPane scrollN;
    JScrollPane scrollS;

    public void setupGui(QuizCard qz) {
        this.qz = qz;
        frame = new JFrame("Gray Garrett LLC Presents: QUIZ CARD FLASH 1.0");

        background = new JPanel();
        background.setLayout(new BoxLayout(background, BoxLayout.Y_AXIS));

        areaN = new JTextArea(10, 20);
        areaS = new JTextArea(10, 20);



        scrollN = new JScrollPane(areaN);
        scrollS = new JScrollPane(areaS);

        labelN = new JLabel("QUESTION");
        labelS = new JLabel("ANSWER");

        buttonNext = new JButton("NEXT");


        frame.getContentPane().add(BorderLayout.CENTER, background);

        frame.setSize(500, 500);


    public void actionPerformed(ActionEvent event) {


        if (list >= qz.getQuestionListSize()) {
            list = 0;

        // areaN.setText("");

    class AnswerListener implements ActionListener {

        public void actionPerformed(ActionEvent event) {

            for (int z = 0; z < qz.getQuestionListSize(); z++) {
                if (!areaN.equals(qz.getQuestion(z))) {
                    areaS.setText(" ");
                    areaS.setText("CUSTOM QUESTION HAS NOT BEEN SAVED!");


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