Taking String values from Arraylist<Object>

Question

I take all my values from the database and put them in one array list<object> i would like to know how to access the value within this arraylist emu, for example TesteLinhas.get(0).toString() or something like return me to where it is allocated in memory, I believe. I would like me to get the value of it. There is some way?

ArrayList linhas = new ArrayList();

        String sql = "SELECT * FROM tb_zerados ORDER BY id ASC";

        conexao.pstm  = conn.prepareStatement(sql);
        conexao.rs = conexao.pstm.executeQuery();

        while(conexao.rs.next()){
            linhas.add(new Object[]{conexao.rs.getInt("id"),
                                    conexao.rs.getInt("numero"),
                                    conexao.rs.getString("ano"),
                                    conexao.rs.getString("nome"),
                                    conexao.rs.getString("estilo"),
                                    conexao.rs.getString("plataforma"),
                                    conexao.rs.getInt("nota")});

        }

        System.out.println(linhas.get(1));

He returns it to me: [Ljava.lang.Object;@28a8f402, and I’d like you to return a String or a Integer.

Answer 1

You’re putting a array within a ArrayList. I don’t recommend doing it this way, but since you did, the solution is to access the array within the ArrayList. It’s like another dimension. That’s how it works:

System.out.println(linhas.get(1)[0]);

The get(1) is taking the line and the [0] is taking the column.

You have to do this for each field, that is, it must go from 0 to 6 since it has 7 fields.

Can make a loop:

for (Object obj : linhas.get(1)) {
    System.out.println(obj);
}

I put in the Github for future reference.

Answer 2

Each line created in this list is of the type array of Object[], when you recover, you have to give a cast of the type (which in this case is Object[]) and to regain the positions which in their case are 7 (of 0 to 6) return to intended position.

Example with all positions:

System.out.println(((Object[])linhas.get(0))[0]);
System.out.println(((Object[])linhas.get(0))[1]);
System.out.println(((Object[])linhas.get(0))[2]);
System.out.println(((Object[])linhas.get(0))[3]);
System.out.println(((Object[])linhas.get(0))[4]);
System.out.println(((Object[])linhas.get(0))[5]);
System.out.println(((Object[])linhas.get(0))[6]);

here is a minimal example, with fictitious data, but that can help you understand how to recover

This will probably solve your problem, but ideally always create a datum tipado with a array using this guy, it is much easier to recover.

Reading:

• Exploring the Arraylist Class in Java
• Class Arraylist
• Java - The Arraylist Class

Answer 3

I do something similar in my app and this can help you.

I have a dbHelper class, where all methods of database manipulation are defined.

This is the method that reads the database and returns a list (as an array) of objects that reflect the table:

//Table Name
private static final String TABLE_RUNS = "runs";
//Table Columns
private static final String _ID = "_id";
private static final String COL_ADDRESS = "address"; 
private static final String COL_NAME = "name"; 
private static final String COL_DATE = "date"; 


List<RunData> getAllRuns() {

    List<RunData> runsList = new ArrayList<>();

    String RUN_SELECT_QUERY = "SELECT * FROM " + TABLE_RUNS;

    SQLiteDatabase db = getReadableDatabase();
    Cursor cursor = db.rawQuery(RUN_SELECT_QUERY, null);

    try {
        if (cursor.moveToFirst()) {
            do {
                RunData runData = new RunData();
                runData.run_id = cursor.getString(cursor.getColumnIndex(_ID));

                runData.name = cursor.getString(cursor.getColumnIndex(COL_NAME));
                runData.address = cursor.getString(cursor.getColumnIndex(COL_RADDRESS));
                runData.date = cursor.getString(cursor.getColumnIndex(COL_DATE));

                runsList.add(runData);

            } while (cursor.moveToNext());
        }
    } catch (Exception e) {
        //Log.d(TAG, "Error while trying to get posts from database");
    } finally {
        if (cursor != null && !cursor.isClosed()) {
            cursor.close();
        }
    }
    return runsList;
}

Use like this:

// Defina os objetos
RunDbHelper runDbHelper;
List<RunData> runList = new ArrayList<>();

// Instancie a classe dbHelper
runDbHelper = RunDbHelper.getInstance(getContext());
// call para ler o banco de dados e retornar uma lista de objetos runData
runList = runDbHelper.getAllRuns();
for (RunData runData : runList) { // percorre a lista de dados, usando runData como container
    // Agora, cada linha da lista (é manipulada como objeto de dados 
    doWhatwEver(runData.name, runData.address, runData.date); 
}

Rundata is a POJO or Javabeans type object that has the same fields as the table. It is easier to manipulate than array indices.