Recompile with -Xlint:unchecked for details Warning?

Question

I wrote this code where when the software starts it takes data from a database (MYSQL control center) and bring them to a table. But when I compile this code 2 errors occurs.

Note: C:\Users\Commander Shepard\Documents\NetBeansProjects\Furniture Management System\src\furnituremanagementsystem\employee.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

My Code:

public class employee extends javax.swing.JFrame {

    // Creates new form employee
    public employee() {
        initComponents();           

        Date now = new Date();
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy/MM/dd");
        datelabel.setText(formatter.format(now));

        try {
            Statement s = DB.getConnection().createStatement();
            DefaultTableModel dtm = (DefaultTableModel) jTable1.getModel();
            dtm.setRowCount(0);
            ResultSet r = s.executeQuery("SELECT * from Employee");
            while (r.next()) {
                Vector v = new Vector();
                v.add(r.getString(1));
                v.add(r.getString(2));
                v.add(r.getString(3));
                v.add(r.getString(4));
                v.add(r.getString(5));
                v.add(r.getString(6));
                v.add(r.getString(7));
                v.add(r.getString(8));
                v.add(r.getString(9));
                v.add(r.getString(10));
                v.add(r.getString(11));
                v.add(r.getString(12));
                v.add(r.getString(13));
                v.add(r.getString(14));

                dtm.addRow(v);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unchecked")
    ...
}

The thing didn't actually affect the program, it's working properly, but I want to know if this is going to be a problem in the future and whether I should do something about this.

Answer 1

That happens when you use generic references. You don't really need to take the warning into consideration, but if you want to see what it is you should compile again with the new argument:

javac programname.java argument

But using generics in Java has many problems as it was added quite late and with all the backward compatibility issues, yeah, we don't need to get into that.