从另一个类调用arraylist方法

Question

How do i call this method in another class?

I need to use the array list inside this method from a class called database helper to compare the value of a variable with this array list in another class(Main Menu).

The idea is that it gets all the values inside the database and checks if the variable from the class Main Menu value is anywhere inside the array list of the class database helper.

  public ArrayList<Phone> retrieveAllPhones() {
        ArrayList<Phone> phoneArrayList
                = new ArrayList<>();
// SELECT * FROM student;
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.query(Phone.TABLE,
                null,// columns
                null,// selection
                null,// selection args
                null,// group by
                null,// having
                null// order by
        );

        if (cursor.moveToFirst()) {
            do {
                Phone phone = new Phone();

                phone.setSenderNum(
                        cursor.getString(cursor.getColumnIndex(Phone.NUM))
                );
                // assign this name to Student

                phone.setMessage(
                        cursor.getString(cursor.getColumnIndex(Phone.MESSAGE))

                );
                phone.setGeo(
                        cursor.getString(cursor.getColumnIndex(Phone.GEO))
                );

                phoneArrayList.add(phone);
            } while (cursor.moveToNext());
        }

Answer 1

I'm not entirely sure I understand your question. I presume the phoneArrayList is the return value, can't you just save the return value and use that? It would help to include the full method at least, preferably the full class.

Answer 2

you can call it by instantiating object from the class like:

ArrayList<Phone> phones = new YourDatabaseHelperClass().retrieveAllPhones();

or change the method to static like:

public static ArrayList<Phone> retrieveAllPhones() {
  ...
}

Then you only need to call it with:

ArrayList<Phone> phones = YourDatabaseHelperClass.retrieveAllPhones();

Answer 3

Possible to access ArrayList from another Class but The ArrayList should be public and static.