IndexOutOfBounds. How should you store data from resultSet into an ArrayList?

0
votes

So, I have a method that (should) return a String containing a data from a sqlite database:

public String getLesson() throws ClassNotFoundException {
    ArrayList list = new ArrayList();

    int selectedColumn = tblOpenLesson.getSelectedColumn();
    int selectedRow = tblOpenLesson.getSelectedRow();
    String name = (String) tblOpenLesson.getModel().getValueAt(selectedRow, selectedColumn);

    try {
        Class.forName("org.sqlite.JDBC");
        Connection con = DriverManager.getConnection("jdbc:sqlite:sql_items.sqlite");
        Statement stmtGetLesson = con.createStatement();
        ResultSet rs = stmtGetLesson.executeQuery("SELECT * FROM lessons WHERE lesson_id  = '" + name + "';");

        if (rs.next()) {
            list.add(rs.getString("lesson"));
        }
    } catch (SQLException e) {
        JOptionPane.showMessageDialog(null, e);
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(openLesson.class.getName()).log(Level.SEVERE, null, ex);
    }

    return (String) list.get(0);
}

and I would use that string to locate a text file by which its content will be displayed on a JTextPane that is located from another class

private void btnOpenLessonPopUpActionPerformed(java.awt.event.ActionEvent evt) {                                                   

    try {
        FileReader fr = new FileReader("Lessons\\" + getLesson() + ".txt"); //this is Line 126

        try (BufferedReader br = new BufferedReader(fr)) {
            mainScreen.lessonPane.read(br, null); //  lessonPane is from another class
            br.close();
        } catch (IOException e) {
            System.out.println(e);
            this.setVisible(false);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(openLesson.class.getName()).log(Level.SEVERE, null, ex);
        }  
    }

however I am getting this error:

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(ArrayList.java:657) at java.util.ArrayList.get(ArrayList.java:433) at mainWindow.openLesson.getLesson(openLesson.java:204) at mainWindow.openLesson.btnOpenLessonPopUpActionPerformed(openLesson.java:126) at mainWindow.openLesson.access$000(openLesson.java:19) at mainWindow.openLesson$1.actionPerformed(openLesson.java:60) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) at java.awt.Component.processMouseEvent(Component.java:6539) at javax.swing.JComponent.processMouseEvent(JComponent.java:3324) at java.awt.Component.processEvent(Component.java:6304) at java.awt.Container.processEvent(Container.java:2239) at java.awt.Component.dispatchEventImpl(Component.java:4889) at java.awt.Container.dispatchEventImpl(Container.java:2297) at java.awt.Component.dispatchEvent(Component.java:4711) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476) at java.awt.Container.dispatchEventImpl(Container.java:2283) at java.awt.Window.dispatchEventImpl(Window.java:2746) at java.awt.Component.dispatchEvent(Component.java:4711) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760) at java.awt.EventQueue.access$500(EventQueue.java:97) at java.awt.EventQueue$3.run(EventQueue.java:709) at java.awt.EventQueue$3.run(EventQueue.java:703) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84) at java.awt.EventQueue$4.run(EventQueue.java:733) at java.awt.EventQueue$4.run(EventQueue.java:731) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74) at java.awt.EventQueue.dispatchEvent(EventQueue.java:730) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

I don't think I have any idea of why this is happening. I'm still new to programming.

3
javasqlitearraylistjdbcresultset
If you are only wanting one column then don't do SELECT * FROM lessons, just select column - Scary Wombat
It's not an error, but you shouldn't use ArrayList as a type (on the left) of a variable because it's a concrete class rather than an interface. You should use List instead. Also, this list is only going to hold strings, so it should be futher constrained with generics (<>). So, ArrayList list = new ArrayList(); should be List<String> list = new ArrayList<>; - Software Engineer

3 Answers

2
votes

Difficult to say without knowing the structure of your data, however, from your query: "SELECT * FROM lessons WHERE lesson_id = '" + name + "';" it seems that you are trying to match the lesson_id with the name of the lesson your are getting.

It could also be that String name = (String) tblOpenLesson.getModel().getValueAt(selectedRow, selectedColumn); doesn't give you what you'd expect.

On another note, you really need to look into Prepared Statements. As is, your application is prone to SQL injection.

Personally, I would also refactor the code so that: 

if (rs.next()) {
    list.add(rs.getString("lesson"));
}

Becomes:

if (rs.next()) {
    return rs.getString("lesson");
}

And this: return (String) list.get(0); becomes return "";.

3
votes

If the sql query doesn't return any rows the last line will throw an exception because your list is empty.

 return (String) list.get(0);

So either change it to

if (!list.isEmpty() {
    return (String) list.get(0);
}
return null; //If list is empty

or even better since you are only interested in the first row you can skip the list and replace 

if (rs.next()) {
    list.add(rs.getString("lesson"));
}

with 

if (rs.next()) {
    return rs.getString("lesson");
}

You still need to return at the end of the method

return null;

Than you use it like this

try {
    String lesson = getLesson();
    if (lesson != null) {
         //open file...
    }
...
0
votes

You are throwing an IndexOutOfBounds exception when trying to retrieve the value at index 0. This would mean that nothing has been added to your ArrayList. Your data is more than likely not a valid row when next() is called.