Question

I have a table 2×2 (2 columns and 2 rows filled) on my database, I’m trying to get the entire table to my array, but when I try to print the result on the console I get NullPointerException. I can’t figure out what I am missing.

Main code:

public static void main(String[] args) {
    mySQLManager Manager = new mySQLManager();
    Manager.Connect();
    String[] Dispositivos = null;
    Dispositivos = Manager.GetDevices();
    for (int i = 0; i < Dispositivos.length; i++){
        System.out.println(Dispositivos[i]);
    }
    Manager.Disconnect();
}

Method:

public String[] GetDevices(){
    String[] Devices = null;
    String query = "SELECT * FROM devices";
    int index = 0;
    try {
        statement = connection.createStatement();
        resultSet = statement.executeQuery(query);
        while(resultSet.next()){
            Devices[index + 0] = resultSet.getString(1);
            Devices[index + 1] = resultSet.getString(2);
            index+=2;
        }
    } catch (SQLException ex) {
        System.out.println("\nNão foi possivel ler os dispositivos do database");
        System.out.print(ex.getMessage());

    }
    return Devices;
}

Error I am getting:

Exception in thread “main” java.lang.NullPointerException at
logictesting.mySQLManager.GetDevices(mySQLManager.java:130) at
logictesting.LogicTesting.main(LogicTesting.java:29) Java Result: 1

Answer 1

The problem is that Devices is null in:

        Devices[index + 0] = resultSet.getString(1);
        Devices[index + 1] = resultSet.getString(2);

The easiest fix might be to turn Devices into an ArrayList since then it would be easy to grow it dynamically.

public String[] GetDevices(){
    List<String> Devices = new ArrayList<String>();
    String query = "SELECT * FROM devices";
    try {
        statement = connection.createStatement();
        resultSet = statement.executeQuery(query);
        while(resultSet.next()){
            Devices.add(resultSet.getString(1));
            Devices.add(resultSet.getString(2));
        }
    } catch (SQLException ex) {
        System.out.println("\nNão foi possivel ler os dispositivos do database");
        System.out.print(ex.getMessage());

    }
    return Devices.toArray(new String[0]);
}