'Can't acces a public method from a public class outside the class in Android Studio

I'm building a SQlite database for a android quiz app. In Helper class I created a public method getAllQuestions(), but for some reason I can't access this method(or any other method in the helper class) in MainActivity. BTW I imported this class to Main but it doesn't help.

this is the code:

public class DB_Helper  extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "PRO_QUIZ";
    public static final  int DATABASE_VERSION = 1;
    private SQLiteDatabase db;

    public  ArrayList<QuestionsDataBase> getAllQuestions() {

        ArrayList<QuestionsDataBase> questionsList = new ArrayList<>();
        db = getReadableDatabase();
        String Projection [] ={
                QuestionTable._ID,
                QuestionTable.Column_Question,
                QuestionTable.Column_Option1,
                QuestionTable.Column_Option2,
                QuestionTable.Column_Option3,
                QuestionTable.Column_Option4,
                QuestionTable.Column_Correct_Ans
        };
        Cursor c = db.query(QuestionTable.Table_Name, Projection, null, null, null, null, null);
        if (c.moveToFirst()) {
            do {
                QuestionsDataBase questions = new QuestionsDataBase();
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Question)));
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option1)));
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option2)));
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option3)));
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option4)));
                questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Correct_Ans)));
                questionsList.add(questions);
            } while (c.moveToNext());
        }
        c.close();
        return questionsList;
    }

However, when I type in Main: DB_Helper. I cant see any methods.

javaandroid


Solution 1:[1]

The method getAllQuestions() is not static. That means that you need an instance of DB_Helper to access that method (you get an instance of an object with the keyword new). So do this:

DB_Helper dbHelper = new DB_Helper();
dbHelper.getAllQuestions();

or alternatively you can declare the method as static this way:

public static ArrayList getAllQuestions(){
    ...
}

And then access it as you wanted in the first palce:

DB_Helper.getAllQuestions();

But beware that in this case (doing it static) you will also need to declare all class variables used in that method as static too:

private static SQLiteDatabase db;

Recommended further reading: Difference between Static methods and Instance methods

Sources

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Source: Stack Overflow

Solution Source
Solution 1

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